Automatic Transfer Switches
Remake for template neutrality (from-scratch field inventory, five-state defaults, parameters and derived fields, schedule deferrals)
Showing changes from Rev 6
to Rev 7
in Automatic Transfer Switches.
---
title: Automatic Transfer Switches
category: Electrical / Power Distribution Equipment
−toc_depth: 3
description: >
− When to use: Automatic transfer switches (ATS) rated 600V and below, commonly 100A through 4000A, used to transfer load between a normal utility source and an emergency or standby source (typically an engine-generator per [[sync/generators]]). Covers contactor-based and switched-neutral types, open-transition, delayed-transition, and closed-transition operation, with optional bypass-isolation construction, listed to UL 1008 and applied in accordance with NFPA 110 and NFPA 70 Articles 700, 701, 702, and 708. Not intended for: Manual transfer switches without automatic operation, medium-voltage automatic source-transfer schemes (primary or secondary selective substation switching), static transfer switches associated with uninterruptible power supplies, paralleling switchgear with multiple generators on a common bus, or generator paralleling controls themselves (see [[sync/generators]] and [[sync/low-voltage-switchgear]]).
+ When to use: Automatic transfer switches rated 1000 V and below, listed to UL 1008, that move a load between a normal source and an alternate source without operator action. Covers the switching mechanism, transition type, bypass-isolation construction, neutral treatment, the controller and its sensing, time delays, exerciser, load management and communications provisions, ratings including withstand and closing and short-time ratings, service-entrance construction, enclosures, identification, factory and field testing, installation, warranty, and spare parts, for switches serving emergency, legally required standby, optional standby, critical operations, and health care essential electrical system loads.
+
+ Not intended for: The system-level design of the emergency and standby power system, including load classification, source selection, transfer scheme, and selective coordination ([[sync/emergency-and-standby-power]]); the engine-generator set and its controls ([[sync/generators]]); the branch topology of a health care essential electrical system ([[sync/healthcare-essential-electrical-systems]]); manual and non-automatic transfer switches; medium-voltage transfer switches and source-transfer schemes above 1000 V; static transfer switches and the transfer of a UPS between its bypass and inverter ([[sync/uninterruptible-power-supply-systems]]); paralleling switchgear with more than one generator on a common bus; and utility-owned switching at the service point.
---
# Scope {toc}
−## This specification covers automatic transfer switch (ATS) equipment rated 600V and below for transferring connected loads between a normal source (typically the utility service) and an alternate source (typically an on-site engine-driven generator). {note}
+## This standard governs automatic transfer switches rated 1000 V and below that sense the condition of two sources, signal an engine-driven or other alternate source to start, transfer the load to the alternate source when it is ready, and return the load to the normal source when it is restored. {note}
−## The transfer switch shall monitor source voltage and frequency, signal the generator to start when the normal source fails or is out of tolerance, transfer the load to the alternate source after the alternate source is stable, and return the load to the normal source after the normal source is restored and re-stable.
+## Three product decisions are made independently of one another and are stated as independent selections in this standard: the switching mechanism, which is the hardware that carries and switches the load; the transition type, which is the sequence in which the two source connections are broken and made; and bypass-isolation construction, which is the addition of a manual path around the automatic mechanism. Every combination is manufactured, and this standard does not assume that one selection implies another. {note}
−## The transfer switch's selection and configuration shall be governed by NFPA 110, NFPA 70 Articles 700/701/702/708, and the project's continuity-of-operations requirements.
+## The switch is the boundary between the normal distribution and the alternate source, so its ratings are fixed by the upstream service and distribution equipment, its pole configuration decides how the alternate source is grounded, its timing decides whether the system meets the code transfer time, and its classification follows from the loads it serves; most of the coordination in this standard runs outward to the standards that govern those interfaces. {note}
−## The Contractor shall coordinate transfer switch ratings and configuration with the upstream service equipment (see [[sync/low-voltage-switchgear]], [[sync/low-voltage-switchboards]], and [[sync/panelboards]]), with the alternate source (see [[sync/generators]]), with the feeders and branch conductors on both sides of the switch (see [[sync/conductors-and-cables]]), and with the grounding and bonding of any separately derived system created by the transfer switch's pole configuration (see [[sync/grounding-and-bonding]]).
+## The following are governed elsewhere and are outside this standard: {note}
−## Equipment identification and warning labels shall follow [[sync/equipment-labeling]].
+- the classification of loads, the selection of the alternate source, the number and segregation of transfer switches, and the transfer scheme ([[sync/emergency-and-standby-power]])
+- the engine-generator set, its controller, and its remote annunciator ([[sync/generators]])
+- the branch assignment and topology of a health care essential electrical system ([[sync/healthcare-essential-electrical-systems]])
+- the switchgear, switchboards, and panelboards on either side of the switch ([[sync/low-voltage-switchgear]], [[sync/low-voltage-switchboards]], [[sync/panelboards]])
+- the feeders on both sides of the switch and their raceways ([[sync/conductors-and-cables]], [[sync/raceways-and-conduit]])
+- the grounding electrode system and the bonding of a separately derived system ([[sync/grounding-and-bonding]])
+- the short-circuit, coordination, and arc-flash studies that establish the ratings and settings the switch is ordered to ([[sync/short-circuit-study]], [[sync/protective-coordination-study]], [[sync/arc-flash-study]])
+- the room the switch occupies ([[sync/electrical-rooms]]) and the concrete pad as a structure ([[sync/concrete-pads]])
+- manual and non-automatic transfer switches, medium-voltage transfer schemes, static transfer switches, and paralleling switchgear
−## This standard covers low-voltage ATS equipment only and does not cover paralleling switchgear that synchronizes multiple generators onto a common bus, static transfer switches that use solid-state semiconductors for sub-cycle transfer in UPS applications, or manual transfer switches operated by hand without automatic control.
+## The location of each transfer switch shall be as indicated on [[drawing: the electrical plans]].
−## Where the project requires paralleling switchgear, static transfer switches, or manual transfer switches, they shall be specified separately.
+## The Contractor shall coordinate the ratings, the neutral treatment, the engine-start interface, and the communications interface of each switch with the standards named in this section before the switch is released for manufacture.
# Referenced Standards {toc}
−## Equipment and installation shall comply with the latest adopted edition of each of the following standards.
+## Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
−## Where the contract documents, the adopted building code, or a referenced standard conflict, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
+## Where the contract documents, the serving utility's requirements, the Authority Having Jurisdiction, or two referenced standards impose conflicting requirements, the more stringent requirement shall govern unless the Engineer of Record directs otherwise in writing.
| Standard | Title |
|----------|-------|
−| UL 1008 | Standard for Transfer Switch Equipment |
−| UL 1008S | Standard for Solid-State Transfer Switches (where applicable) |
−| NFPA 110 | Standard for Emergency and Standby Power Systems |
−| NFPA 111 | Standard on Stored Electrical Energy Emergency and Standby Power Systems |
−| NFPA 70 | National Electrical Code (Articles 700, 701, 702, 708, 230, 250) |
+| UL 1008 | Transfer Switch Equipment |
+| UL 489 | Molded-Case Circuit Breakers, Molded-Case Switches, and Circuit-Breaker Enclosures |
+| UL 1066 | Low-Voltage AC and DC Power Circuit Breakers Used in Enclosures |
+| NFPA 70 | National Electrical Code (Articles 110, 230, 250, 517, 700, 701, 702, and 708) |
| NFPA 70E | Standard for Electrical Safety in the Workplace |
−| NFPA 99 | Health Care Facilities Code (where applicable) |
−| IEEE 446 | Recommended Practice for Emergency and Standby Power Systems (Orange Book) |
−| IEEE 241 | Recommended Practice for Electric Power Systems in Commercial Buildings (Gray Book) |
−| IEEE C62.41 | Recommended Practice on Surge Voltages in Low-Voltage AC Power Circuits |
−| NEMA ICS 10-1 | AC Transfer Switch Equipment |
+| NFPA 99 | Health Care Facilities Code |
+| NFPA 101 | Life Safety Code |
+| NFPA 110 | Standard for Emergency and Standby Power Systems |
+| NEMA ICS 10 Part 1 | Industrial Control and Systems: AC Transfer Switch Equipment |
| NEMA 250 | Enclosures for Electrical Equipment (1000 Volts Maximum) |
−| IBC | International Building Code (seismic and importance factors) |
−| ASCE 7 | Minimum Design Loads and Associated Criteria for Buildings and Other Structures |
−| ICC ES AC156 | Acceptance Criteria for Seismic Certification by Shake-Table Testing |
−| ANSI/NETA ATS | Standard for Acceptance Testing Specifications for Electrical Power Equipment |
+| UL 50E | Enclosures for Electrical Equipment, Environmental Considerations |
+| IEEE 1547 | Standard for Interconnection and Interoperability of Distributed Energy Resources with Associated Electric Power Systems Interfaces |
+| ASCE 7 | Minimum Design Loads and Associated Criteria for Buildings and Other Structures (Chapter 13) |
+| ICC-ES AC156 | Acceptance Criteria for Seismic Certification by Shake-Table Testing of Nonstructural Components |
+| ANSI/NETA ATS | Standard for Acceptance Testing Specifications for Electrical Power Equipment and Systems |
# Submittals {toc}
## Action Submittals {toc}
−### Contractor shall submit the following for review prior to fabrication.
−### Installation shall not proceed until the corresponding submittals have been reviewed and returned.
+### The Contractor shall submit the following for review before any transfer switch is released for manufacture:
−- Product data for the transfer switch, controller, and accessories, with the UL 1008 listing mark indicated
−- Shop drawings showing overall dimensions, conduit entry locations, mounting details, and required working clearances
−- Single-line diagram showing the transfer switch in context, including normal source, alternate source, load, ratings, and pole configuration (3-pole or 4-pole)
−- Control and wiring schematics, including engine-start contacts, signal interfaces, and any communications interfaces
−- Withstand and Closing Rating (WCR) tables coordinated with the upstream overcurrent device(s) actually used on the project
−- Seismic certification documentation per IBC/ASCE 7 where required
−- Manufacturer's recommended time-delay settings and the project-specific values proposed by the Contractor for Engineer review
−- Factory production-test report covering each unit furnished
+- product data for the switch, the controller, and every accessory, identifying the UL 1008 listing of the complete assembly and the emergency-system listing where the switch serves an Article 700 or Article 701 system
+- shop drawings giving overall dimensions, weight, mounting arrangement, conduit entry areas, lug sizes and conductor ranges, and the working clearance the manufacturer requires
+- a one-line diagram of the switch showing the normal source, the alternate source, the load, the number of poles, the neutral treatment, and any integral overcurrent device
+- control schematics showing the engine-start contacts, the auxiliary contacts, the load-management inputs and outputs, and the communications interface
+- the withstand and closing rating and, where selected, the short-time withstand rating of the switch, together with the UL 1008 listing data that ties each rating to the upstream overcurrent device or fuse actually installed on the project
+- the proposed initial value of every programmable time delay and sensing set point, on a settings record the Engineer of Record will review
+- the seismic certification for the switch, where the datasheet requires one
```datasheet
−label: Action Submittals Required
+label: Action Submittals
type: checkbox
options:
− - "Product data with UL 1008 listing"
− - "Shop drawings (dimensions, conduit entries, clearances)"
− - "Single-line diagram showing ATS in context"
− - "Control and wiring schematics"
− - "WCR tables coordinated to project OCPDs"
− - "Seismic certification (where required)"
− - "Proposed time-delay settings"
− - "Factory production-test report"
+ - "Product data with UL 1008 listing of the complete assembly"
+ - "Shop drawings with dimensions, mounting, conduit entry, and lug data"
+ - "One-line diagram of the switch"
+ - "Control schematics"
+ - "Withstand and closing rating and short-time rating with the listing data for the upstream device"
+ - "Proposed settings record"
+ - "Seismic certification"
default:
− - "Product data with UL 1008 listing"
− - "Shop drawings (dimensions, conduit entries, clearances)"
− - "Single-line diagram showing ATS in context"
− - "Control and wiring schematics"
− - "WCR tables coordinated to project OCPDs"
− - "Proposed time-delay settings"
− - "Factory production-test report"
+ - "Product data with UL 1008 listing of the complete assembly"
+ - "Shop drawings with dimensions, mounting, conduit entry, and lug data"
+ - "One-line diagram of the switch"
+ - "Control schematics"
+ - "Withstand and closing rating and short-time rating with the listing data for the upstream device"
+ - "Proposed settings record"
```
+### A transfer switch shall not be released for manufacture until the action submittals covering it have been reviewed and returned.
+
+### The withstand and closing rating is the submittal item that most often comes back wrong, because the rating printed in a catalog is the highest rating the switch holds with the most favorable upstream device, and the rating that applies on the project is the one the listing assigns to the device actually installed ahead of the switch. {note}
+
+## Informational Submittals {toc}
+
+### The Contractor shall submit the following with or before the action submittals:
+
+- the manufacturer's qualification statement required under Quality Assurance
+- the serving utility's written approval of parallel operation, where the datasheet selects a closed-transition or soft-load transition type
+- the factory test procedure, where the datasheet selects witnessed factory testing
+- the field testing firm's qualification statement and the proposed field test procedure
+- the seismic anchorage calculation and anchor detail for the installed condition
+
+```datasheet
+label: Informational Submittals
+type: checkbox
+options:
+ - "Manufacturer's qualification statement"
+ - "Utility approval of parallel operation"
+ - "Factory test procedure"
+ - "Field testing firm qualification and test procedure"
+ - "Seismic anchorage calculation and detail"
+default:
+ - "Manufacturer's qualification statement"
+ - "Field testing firm qualification and test procedure"
+ - "Seismic anchorage calculation and detail"
+```
+
## Closeout Submittals {toc}
−### Contractor shall provide the following at substantial completion before the transfer switch is accepted.
+### The Contractor shall submit the following before any transfer switch is accepted:
−- Operation and maintenance manuals, including the controller programming and setting record as commissioned
−- As-built single-line and control schematics reflecting any field changes
−- Field acceptance test reports per NETA ATS and per NFPA 110 §8 where applicable
−- Manufacturer startup and commissioning report
−- Warranty documentation
−- Spare parts inventory with reorder information
+- the certified factory production test report for each switch, identified by serial number
+- the field acceptance test report for each switch, giving every measured value, the acceptance criterion applied, and the tester's determination
+- the manufacturer's field startup report, where the datasheet requires manufacturer startup
+- the installation acceptance test record required by NFPA 110 Chapter 7, where the switch serves a system classified under NFPA 110
+- the settings record as commissioned, giving the final value of every programmable time delay, sensing set point, exerciser setting, and load-management setting
+- as-built one-line and control schematics reflecting every field change
+- operation and maintenance data giving the controller programming procedure, the manual operation procedure, the bypass operating sequence where furnished, the inspection intervals, and the torque values for every accessible connection
+- the warranty documentation for the switch and for the installation
+- a signed receipt from the Owner for the spare parts delivered
```datasheet
−label: Required Closeout Submittals
+label: Closeout Submittals
type: checkbox
options:
− - "Operation and maintenance manuals with setting record"
− - "As-built single-line and control schematics"
− - "Field acceptance test reports (NETA ATS / NFPA 110 §8)"
− - "Manufacturer startup and commissioning report"
+ - "Certified factory production test reports"
+ - "Field acceptance test reports"
+ - "Manufacturer field startup report"
+ - "NFPA 110 installation acceptance test record"
+ - "Settings record as commissioned"
+ - "As-built one-line and control schematics"
+ - "Operation and maintenance data"
- "Warranty documentation"
− - "Spare parts inventory with reorder information"
+ - "Spare parts receipt"
default:
− - "Operation and maintenance manuals with setting record"
− - "As-built single-line and control schematics"
− - "Field acceptance test reports (NETA ATS / NFPA 110 §8)"
− - "Manufacturer startup and commissioning report"
+ - "Certified factory production test reports"
+ - "Field acceptance test reports"
+ - "Settings record as commissioned"
+ - "As-built one-line and control schematics"
+ - "Operation and maintenance data"
- "Warranty documentation"
− - "Spare parts inventory with reorder information"
```
+### The settings record is the document a successor technician reads before touching the controller, and a switch whose commissioned settings exist only in its own memory loses them with the first controller replacement. {note}
+
# Quality Assurance {toc}
## Manufacturer Qualifications {toc}
−### The transfer switch shall be the product of a manufacturer regularly engaged in the production of UL 1008 listed transfer switch equipment, with a minimum of five years of documented production experience in the rating class furnished.
+### The transfer switch shall be produced by a manufacturer that has manufactured UL 1008 listed transfer switches of the same mechanism type and ampere range for not less than the period indicated in the datasheet.
−### The manufacturer shall maintain a North American service organization capable of dispatching a factory-trained technician on-site within 24 hours of notification.
+```datasheet
+label: Minimum Manufacturer Production Experience
+type: range
+unit: years
+options:
+ min: 0
+ max: 20
+ setpoints: [0, 3, 5, 10, 20]
+default: 5
+```
−## Listing and Labeling {toc}
+### The manufacturer shall maintain a factory-trained field service organization able to reach the site, and shall state in the qualification statement the location of the nearest service center and the parts stocked there.
−### The transfer switch shall be listed and labeled to UL 1008 as a complete assembly — power switching device, controller, and enclosure — by a Nationally Recognized Testing Laboratory.
+## UL 1008 Listing {toc}
−### UL 1008 listing of components individually is not acceptable; the assembly as furnished shall bear the listing mark.
+### The transfer switch shall be listed and labeled to UL 1008 as a complete assembly, comprising the power switching mechanism, the controller, the bypass-isolation mechanism where furnished, and the enclosure, by a Nationally Recognized Testing Laboratory.
−### Transfer switches serving emergency systems per NEC Article 700 shall be UL 1008 listed.
+### A switch whose components are individually listed but whose assembly is not shall not be furnished.
−### UL 1008 listing of emergency-system transfer switches is a code requirement, not a project preference. {note}
+### Where the switch serves an Article 700 emergency system or an Article 701 legally required standby system, it shall be electrically operated and mechanically held and shall be listed for emergency system use in accordance with NEC 700.5(C) or NEC 701.5(C).
−### Where the project includes health care facilities subject to NFPA 99 and NEC Article 517, the transfer switch shall additionally be suitable for the essential electrical system branch it serves (life safety, critical, or equipment branch) and shall be applied accordingly.
+### Where the switch serves a health care essential electrical system, it shall in addition satisfy NEC Article 517 and NFPA 99 for the branch it serves, as assigned under [[sync/healthcare-essential-electrical-systems]].
−## Source Limitations {toc}
+### Where the switch is furnished with integral overcurrent protection, the protective device shall be listed to UL 489 or UL 1066 as applicable and the combination shall be covered by the UL 1008 listing of the assembly.
−### The transfer switch, its controller, and all factory-installed accessories shall be furnished by a single manufacturer responsible for the complete assembly.
+## Field Testing Firm Qualifications {toc}
−### Combining a power switching device from one manufacturer with a third-party controller is not acceptable for global applications under this standard.
+### Field acceptance testing shall be performed by an independent testing firm qualified in accordance with [[sync/electrical-acceptance-testing]].
−## Testing Personnel Qualifications {toc}
+### The technician who performs the functional and timing tests shall have documented experience commissioning the controller family furnished.
−### Field acceptance testing shall be performed by a firm regularly engaged in testing low-voltage power equipment, employing technicians certified by NETA or equivalent.
+# Environmental and Service Conditions {toc}
−### Testing personnel shall have a minimum of three years of experience testing transfer switch equipment and shall be familiar with the controller furnished.
+## Ambient Temperature {toc}
−# Environmental and Service Conditions {toc}
+### The transfer switch shall carry its ratings continuously at the design ambient temperature of the space it is installed in.
−## The transfer switch shall be suitable for continuous operation under the ambient conditions of the installed location.
+### The design ambient temperature for a switch installed indoors shall be as indicated in the datasheet.
−## Where conditions exceed the manufacturer's standard ratings, the Contractor shall notify the manufacturer and apply derating or alternative construction as required.
+```datasheet
+label: Indoor Design Ambient Temperature
+type: range
+unit: °C
+options:
+ min: 25
+ max: 50
+ setpoints: [25, 30, 40, 50]
+default: 40
+```
−## Ambient and Altitude {toc}
+### A 40°C ambient is the rating basis of UL 1008 and NEMA ICS 10, so a 40°C indoor design ambient is the condition at which the nameplate rating applies without correction; a higher value covers a generator room or a mechanical space whose ventilation cannot hold the standard ambient at design load, at the cost of a larger frame for the same load. {note}
−### The design ambient temperature range and the installation altitude shall be as indicated in the datasheet.
+### A switch installed outdoors or in a space that follows the outdoor temperature shall be rated for [[parameter: site-ambient-temperature-maximum]] where that temperature exceeds 40°C, and the manufacturer shall state the correction applied.
+## Altitude {toc}
+
+### The transfer switch shall be de-rated for [[parameter: altitude]] in accordance with the manufacturer's published correction factors where the altitude exceeds the rating basis of the listing.
+
+### Air thins with altitude, which reduces both the dielectric strength of the clearances inside the switch and the convective cooling of its contacts and conductors, so a switch rated at sea level carries less current and less insulation margin at elevation than its nameplate states. {note}
+
+## Condensation Control {toc}
+
+### The space heater provision for the enclosure shall be as indicated in the datasheet.
+
```datasheet
−label: Ambient Temperature (Operating)
−type: select
−unit: °C
+label: Enclosure Space Heater
+type: radio
options:
− - "0 to 40°C (standard)"
− - "-20 to 40°C (cold-climate indoor)"
− - "-30 to 50°C (extended outdoor)"
−default: "0 to 40°C (standard)"
+ - "No space heater"
+ - "Space heater with thermostat"
+ - "Space heater with thermostat and humidistat"
```
+### A switch that stands de-energized on its alternate source side in an unconditioned space cycles through the dew point with every cold night, and the condensation that forms on the contacts, the controller, and the insulating barriers is the mechanism behind most failures on first transfer after a long idle period. {note}
+
+### Where the switch is installed outdoors or in a space that is not conditioned, a space heater shall be furnished unless the datasheet selects no space heater.
+
+### A space heater shall be powered from the load side of the switch, or from a separate source that remains available when either source is lost, so that it operates regardless of which source is carrying the load.
+
+## Seismic Qualification {toc}
+
+### The seismic certification required for the transfer switch shall be as indicated in the datasheet.
+
```datasheet
−label: Installation Altitude
+label: Seismic Certification Requirement
type: select
+derived: "[[parameter: seismic-design-category]] and the component importance factor assigned to the switch under ASCE 7 Chapter 13"
options:
− - "Below 6,600 ft (2,000 m) — no derating"
− - "6,600 to 9,900 ft (2,000 to 3,000 m) — derating required"
− - "Above 9,900 ft (3,000 m) — consult manufacturer"
−default: "Below 6,600 ft (2,000 m) — no derating"
+ - "No seismic certification required"
+ - "Anchorage design only, in accordance with ASCE 7 Chapter 13"
+ - "Special certification of the switch as an active component in accordance with ASCE 7 Section 13.2.2"
+default: derived
```
−## Outdoor and Unconditioned Installations {toc}
+### Anchorage keeps the switch on its wall or floor; special certification demonstrates that the switch still transfers after the design earthquake, which ASCE 7 requires of a component whose importance factor is above 1.0. A switch serving egress lighting, fire pumps, smoke control, or another life-safety load carries an importance factor of 1.5 under ASCE 7, and so does a switch needed for the continued operation of a Risk Category IV facility. {note}
−### Whether an enclosure heater is furnished shall be as indicated in the datasheet.
+### Where special certification is required, the certification shall be by shake-table test in accordance with ICC-ES AC156 or by analysis accepted by the Authority Having Jurisdiction, and the certificate shall cover the switch as furnished, including the controller, the bypass-isolation mechanism where furnished, and the enclosure.
+# System Classification {toc}
+
+## The article of NFPA 70 that governs the loads a switch serves fixes its transfer time, its wiring separation, its listing, its labeling, and whether NFPA 110 applies to it, so the classification is stated on the datasheet as a derived value rather than decided at the switch. {note}
+
+## The NEC article and, in a health care facility, the essential electrical system branch served by the switch shall be as indicated in the datasheet.
+
```datasheet
−label: Enclosure Heater
−type: radio
+label: NEC Article and Branch Served
+type: select
+derived: "the classification of the loads the switch serves on the project's load schedules under NFPA 70 Articles 700, 701, 702, and 708, and in a health care facility the essential electrical system branch assignment under NFPA 99"
options:
− - "Not required (climate-controlled indoor space)"
− - "Provided, thermostat-controlled"
+ - "Article 700 emergency system"
+ - "Article 701 legally required standby system"
+ - "Article 702 optional standby system"
+ - "Article 708 critical operations power system"
+ - "Health care essential electrical system, life safety branch"
+ - "Health care essential electrical system, critical branch"
+ - "Health care essential electrical system, equipment branch"
+default: derived
```
−### Transfer switches installed outdoors, in unconditioned spaces, or in mechanical and generator rooms shall account for the wider temperature swings, condensation, and dust exposure of those locations.
+## A transfer switch serving an Article 700 emergency system shall supply only emergency loads in accordance with NEC 700.5(D).
−### Outdoor and unconditioned installations should include a thermostatically controlled enclosure heater to prevent condensation on the power conductors, controller, and contact surfaces.
+## The NFPA 110 level of the system the switch serves shall be as indicated in the datasheet.
−## Seismic Requirements {toc}
+```datasheet
+label: NFPA 110 Level
+type: select
+derived: "the NEC article the switch serves and the level the adopted code assigns to that system under NFPA 110 Chapter 4, NFPA 101, and NFPA 99"
+options:
+ - "Level 1"
+ - "Level 2"
+ - "Not classified under NFPA 110"
+default: derived
+```
−### The seismic certification basis shall be as indicated in the datasheet.
+## The NFPA 110 type of the system the switch serves shall be as indicated in the datasheet.
```datasheet
−label: Seismic Certification
+label: NFPA 110 Type
type: select
−drawing_ref: "structural drawings"
+derived: "the NEC article the switch serves, with the maximum restoration time of 10 seconds under NEC 700.12 and 60 seconds under NEC 701.12, and the type the adopted code assigns under NFPA 110 Chapter 4"
options:
− - "Not required"
− - "IBC/ASCE 7 — Importance Factor 1.0"
− - "IBC/ASCE 7 — Importance Factor 1.5 (essential facility / emergency system)"
− - "OSHPD pre-approval (California healthcare)"
−default: deferred
+ - "Type U"
+ - "Type 10"
+ - "Type 60"
+ - "Type 120"
+ - "Type M"
+ - "Not classified under NFPA 110"
+default: derived
```
−### The Seismic Design Category and Importance Factor are established by the project's structural design; the electrical scope adopts them rather than setting them. {note}
+## NFPA 110 classifies an emergency power supply system by level, type, and class. Level 1 applies where failure of the system could result in loss of human life or serious injury, and NFPA 101 and NFPA 99 assign Level 1 to egress illumination and to health care essential electrical systems; Level 2 applies where failure is less critical to life and safety. The type is the maximum time from loss of the normal source to load restoration, and the class is the minimum runtime, which is a property of the alternate source and its fuel rather than of the switch. An Article 702 optional standby system is outside NFPA 110 unless the adopted code or the Owner brings it in. {note}
−### Where required by the applicable building code, the transfer switch shall be seismically certified by shake-table testing per ICC ES AC156 or by analysis per ASCE 7, including the controller and any accessories as installed.
+## A Type U restoration cannot be achieved by a transfer switch and an engine-driven source alone, because the engine must crank, start, and stabilize before it can accept load; where the datasheet derives Type U, the uninterrupted transfer is provided by a stored-energy source under [[sync/uninterruptible-power-supply-systems]], and this switch transfers the input of that source within the time the datasheet derives for the article it serves. {note}
−### Transfer switches serving emergency systems, life-safety branches, or essential facilities frequently carry an importance factor of 1.5 and shall be certified accordingly.
−
# Ratings {toc}
−## Amperage Rating {toc}
+## Continuous Current Rating {toc}
−### The continuous current rating shall be as indicated in the datasheet.
+### The continuous current rating of the switch shall be as indicated in the datasheet.
```datasheet
label: Continuous Current Rating
type: range
unit: A
−drawing_ref: "one-line diagram"
+drawing_ref: "the one-line diagram"
options:
− min: 100
− max: 4000
− setpoints: [100, 150, 200, 260, 400, 600, 800, 1000, 1200, 1600, 2000, 2600, 3000, 4000]
+ min: 30
+ max: 5000
+ setpoints: [30, 40, 60, 70, 100, 125, 150, 200, 225, 260, 300, 400, 600, 800, 1000, 1200, 1600, 2000, 2500, 3000, 4000, 5000]
default: deferred
```
−### The transfer switch shall be rated for the continuous load current it serves.
+### The switch shall be listed for total system load, so that it carries its full ampere rating continuously with any combination of resistive, inductive, motor, and tungsten-lamp load.
−### UL 1008 transfer switches are typically rated for total system load and shall not be loaded above 100% of the nameplate rating unless specifically listed as continuous-duty for 100% application.
+### Where the listing restricts the switch for a class of load, the restriction shall be shown on the nameplate, and the switch shall not be applied to that class of load beyond the restriction.
−### The amperage rating shall be selected to match the upstream feeder ampacity and the downstream load with appropriate margin for future growth.
+### A UL 1008 switch listed for total system load carries 100 percent of its rating continuously, which differs from the 80 percent continuous loading convention that applies to a circuit breaker; the rating is therefore compared directly against the calculated load, and a switch is not oversized to recover a derating that does not exist. {note}
−## Voltage, Phases, and Frequency {toc}
+### The continuous current rating shall be not less than the rating of the overcurrent device ahead of the switch on either source, unless the switch is separately protected on the load side in a manner the listing covers.
−### The nominal system voltage and configuration shall be as indicated in the datasheet.
+## Voltage and Frequency {toc}
+### The system voltage of the switch shall be as indicated in the datasheet.
+
```datasheet
label: System Voltage
type: select
−drawing_ref: "one-line diagram"
+drawing_ref: "the one-line diagram"
options:
− - "120/240V 1Φ 3-wire"
− - "120/208V 3Φ 4-wire"
− - "277/480V 3Φ 4-wire"
− - "480V 3Φ 3-wire"
− - "347/600V 3Φ 4-wire"
+ - "120 V, 1Φ, two-wire"
+ - "120/240 V, 1Φ, three-wire"
+ - "208Y/120 V, 3Φ, four-wire"
+ - "240 V, 3Φ, three-wire"
+ - "240/120 V, 3Φ, four-wire high-leg delta"
+ - "480Y/277 V, 3Φ, four-wire"
+ - "480 V, 3Φ, three-wire"
+ - "600Y/347 V, 3Φ, four-wire"
+ - "600 V, 3Φ, three-wire"
default: deferred
```
−### The number of phases and the number of wires are fixed by the system voltage selected, so they are not offered as separate selections. {note}
+### The number of phases and the number of wires follow from the system voltage selected, and the number of switched poles follows from the wires and the neutral treatment selected under this standard. {note}
−### The 347/600V option applies to systems served at 347/600V, which are encountered in some Canadian and large-industrial installations; equipment for those systems is a distinct product family from 277/480V equipment and is not interchangeable with it. {note}
+### The rated frequency of the switch shall be as indicated in the datasheet.
−### The system frequency shall be as indicated in the datasheet.
−
```datasheet
−label: System Frequency
+label: Rated Frequency
type: radio
−unit: Hz
options:
- "60 Hz"
…2 unchanged lines
```
−### 60 Hz is the North American norm and is the datasheet default; a 50 Hz transfer switch and controller are a distinct product selection, available for the exported or 50 Hz-served installations that need them. {note}
+## Withstand and Closing Rating {toc}
−## Withstand and Closing Rating (WCR) / Short-Circuit Current Rating (SCCR) {toc}
+### UL 1008 establishes the withstand and closing rating of a transfer switch as the prospective short-circuit current the switch withstands without damage and closes onto, in combination with a stated upstream overcurrent device; the same switch carries a different rating with each device it was tested with, so the rating is a property of the pairing and not of the switch alone. {note}
−### UL 1008 establishes the Withstand and Closing Rating (WCR) for a transfer switch — the maximum prospective short-circuit current the switch can withstand without damage and onto which it can close. {note}
+### The basis on which the withstand and closing rating of the switch is established shall be as indicated in the datasheet.
−### The basis on which the Withstand and Closing Rating is established shall be as indicated in the datasheet.
−
```datasheet
label: Withstand and Closing Rating Basis
type: select
options:
− - "Specific breaker (manufacturer and frame named on UL 1008 tables)"
− - "Any-breaker rating (less restrictive, typically a lower kA value)"
− - "Current-limiting fuse (Class L, RK1, or J as listed)"
− - "Integral overcurrent protection (service entrance rated ATS)"
+ - "Specific-breaker rating, with the upstream breaker named in the listing"
+ - "Any-breaker rating"
+ - "Current-limiting fuse rating"
+ - "Integral overcurrent device rating"
```
−### The rating basis follows from the overcurrent device actually installed upstream, which is a project coordination outcome, so the field carries no default. {note}
+### A specific-breaker rating is the highest rating a switch holds, and it depends on the exact breaker named in the listing remaining upstream for the life of the installation; an any-breaker rating holds with any listed breaker of the stated frame and trip range at a lower current; a fuse rating holds with a current-limiting fuse of the stated class and rating and reaches the highest currents; an integral-device rating applies where the switch carries its own overcurrent device and is what a service-entrance switch is listed with. {note}
−### The available fault current at the transfer switch terminals shall be as indicated in the datasheet.
+### The withstand and closing rating of the switch shall be as indicated in the datasheet.
```datasheet
−label: Available Fault Current at ATS Terminals
+label: Withstand and Closing Rating
type: range
unit: kA
−drawing_ref: "short-circuit study"
+drawing_ref: "the one-line diagram"
options:
min: 10
max: 200
− setpoints: [10, 22, 35, 42, 65, 85, 100, 200]
+ setpoints: [10, 14, 18, 22, 25, 30, 35, 42, 50, 65, 85, 100, 150, 200]
default: deferred
```
−### The Withstand and Closing Rating of the transfer switch shall be as indicated in the datasheet.
+### The withstand and closing rating shall equal or exceed the available fault current at the switch terminals from either source as established under [[sync/short-circuit-study]], with the upstream overcurrent device that the study and [[sync/protective-coordination-study]] fix for that source.
−```datasheet
−label: Withstand and Closing Rating (WCR)
−type: range
−unit: kA
−drawing_ref: "short-circuit study"
−options:
− min: 22
− max: 200
− setpoints: [22, 35, 42, 65, 85, 100, 200]
−default: deferred
−```
+### The Contractor shall not select a withstand and closing rating from the interrupting rating of the upstream breaker alone.
−### The WCR is established by test in combination with a specific upstream overcurrent protective device (specific manufacturer and frame, or any-manufacturer molded-case breaker of a given trip rating, or current-limiting fuses of a stated class and rating), and the available WCR for a given switch is therefore a function of what is installed upstream. {note}
+### Where the upstream overcurrent device on either source is substituted after the switch is ordered, the Contractor shall re-verify the withstand and closing rating against the UL 1008 listing data for the substituted device before the switch is energized.
−### The WCR of the transfer switch shall equal or exceed the available fault current at the terminals as determined by the project short-circuit study (see [[sync/short-circuit-study]]).
+## Short-Time Withstand Rating {toc}
−### The Contractor shall not select a WCR based on the upstream breaker rating alone.
+### Where the upstream breaker is set with a short-time delay to achieve the selective coordination NEC 700.32, 701.32, or 708.54 requires, the switch must carry the fault current for the full length of that delay before the breaker opens, and a switch rated only to withstand the instantaneous clearing of the breaker is not rated for that duty. {note}
−### A substitution of an equivalent-amperage breaker from a different manufacturer can void the rating because the UL 1008 tables tie the WCR to a specific upstream device. {note}
+### The short-time withstand duration of the switch shall be as indicated in the datasheet.
−### Where the upstream overcurrent device is changed, the WCR shall be re-verified against the latest UL 1008 listing data.
+```datasheet
+label: Short-Time Withstand Duration
+type: range
+unit: cycles
+derived: "the short-time delay setting of the upstream overcurrent device on each source as established in the protective device coordination study, with zero where the device clears instantaneously"
+options:
+ min: 0
+ max: 30
+ setpoints: [0, 3, 18, 30]
+default: derived
+```
−## Service Entrance Rating {toc}
+### A duration of zero records that no short-time rating is required, which is the case where the upstream device has no short-time delay or where the switch is protected by current-limiting fuses. {note}
−### A service-entrance-rated transfer switch combines the service disconnect, the service main overcurrent device, and the transfer switch into a single listed assembly. {note}
+### Where a short-time rating is required, the switch shall be listed under UL 1008 for the short-time current and duration that the upstream device's short-time delay imposes, and the short-time current shall be not less than the available fault current at the switch terminals.
−### Whether the transfer switch is service entrance rated shall be as indicated in the datasheet.
+## Service-Entrance Construction {toc}
+### Whether the switch is furnished as service equipment shall be as indicated in the datasheet.
+
```datasheet
−label: Service Entrance Rated
+label: Service-Entrance Construction
type: radio
−drawing_ref: "one-line diagram"
+drawing_ref: "the one-line diagram"
options:
− - "Not service entrance rated"
− - "Service entrance rated with integral main overcurrent device"
+ - "Not service equipment"
+ - "Service equipment with integral service disconnect and overcurrent device"
default: deferred
```
−### Service entrance construction simplifies the equipment layout but ties the transfer switch's WCR to the integral overcurrent device. {note}
+### A service-entrance switch combines the service disconnecting means, the service overcurrent device, and the transfer switch in one listed enclosure, which removes a separate piece of service equipment from the layout and ties the withstand and closing rating of the switch to the integral device. {note}
−### The Contractor shall confirm that the integral device's interrupting rating, ground-fault protection, and metering provisions satisfy NEC Article 230 for the project before selecting a service-entrance-rated transfer switch.
+### Where the datasheet selects service-entrance construction, the switch shall be listed as service equipment, shall provide the service disconnecting means and overcurrent protection NEC Article 230 requires, and shall be furnished with the neutral disconnect link and the grounding provisions [[sync/electrical-service-entrance]] requires at the service.
−# The transfer switch shall consist of a mechanically interlocked, double-throw power switching mechanism, a microprocessor-based controller, and an enclosure.
+### Where the datasheet selects service-entrance construction on a solidly grounded wye system of more than 150 V to ground with a service disconnect rated 1000 A or more, the integral overcurrent device shall be furnished with ground-fault protection of equipment in accordance with NEC 230.95.
−# The power switching mechanism shall be electrically operated and mechanically held in either source position so that no continuous power is required to maintain the connection.
+### The integral overcurrent protection furnished with a switch that is not service equipment shall be as indicated in the datasheet.
+```datasheet
+label: Integral Overcurrent Protection
+type: select
+options:
+ - "None"
+ - "On the normal source only"
+ - "On the alternate source only"
+ - "On both sources"
+```
+
+### Where integral overcurrent protection is selected, the switching mechanism shall be of a type on which the protective function is covered by the UL 1008 listing of the assembly, and the device ratings and settings shall be as indicated on [[drawing: the one-line diagram]].
+
# Power Switching Mechanism {toc}
−## The power switching mechanism type shall be as indicated in the datasheet.
+## Mechanism Type {toc}
+### The power switching mechanism type shall be as indicated in the datasheet.
+
```datasheet
label: Switching Mechanism Type
type: radio
options:
− - "Contactor-based (electrically operated, mechanically held)"
− - "Power-frame breaker pair, factory-integrated and interlocked"
− - "Molded-case switch pair, factory-integrated and interlocked"
−default: "Contactor-based (electrically operated, mechanically held)"
+ - "Contactor type, double-throw"
+ - "Molded-case switch or molded-case breaker pair"
+ - "Power circuit breaker pair"
+default: "Contactor type, double-throw"
```
−## The power switching mechanism shall be a single, integrated double-throw device — not two independent breakers tied together by an external interlock.
+### A contactor-type mechanism is one double-throw device that cannot rest in both positions, transfers in a few cycles, and has the longest mechanical life and the smallest footprint of the three types, and it is the construction the large majority of switches are built on across the ampere range. A breaker pair transfers more slowly and depends on an interlock to prevent both breakers closing, and it is used where the switch must also provide overcurrent protection, where the frame exceeds what a contactor mechanism is built in, or where closed-transition control needs each source to be opened and closed independently. {note}
−## Mechanical interlocking shall prevent simultaneous connection of both sources to the load, except in closed-transition operation, where overlapping connection is permitted for a controlled, brief interval (see the Transfer Type requirements below).
+### The mechanism shall be electrically operated and mechanically held in each source position, so that no continuous control power is needed to maintain either connection and loss of control power does not change the switch position.
−## The switching contacts shall be silver-alloy, designed for the inrush and interrupting duty associated with the connected load, and shall be inspectable and replaceable as a field-serviceable assembly.
+### The mechanism shall be interlocked mechanically so that the two sources cannot be connected to the load at the same time, except during the controlled parallel interval of a closed-transition or soft-load transfer selected under this standard.
−## A contactor-based mechanism is the default for typical emergency and standby applications because it provides fast transfer (a few cycles), long mechanical life, and a compact footprint. {note}
+### Where a breaker pair is selected, the two breakers shall be interlocked mechanically as well as electrically, and the assembly shall be listed to UL 1008 as a transfer switch rather than as two breakers with an interlock kit.
−## Breaker-based mechanisms are commonly used for large frames (3000A and above), for closed-transition switching where independent open/close control of each source is required, and where the transfer switch must also provide upstream or downstream overcurrent protection in a service entrance configuration. {note}
+### The main contacts shall be silver alloy, rated for the inrush and interrupting duty of the connected load class, and shall be inspectable and replaceable in the field without removing the switch from its enclosure.
−# Manual Operation {toc}
+### Arc chutes or arc barriers shall be furnished on each pole and shall be removable for contact inspection.
−## The transfer switch shall include a means for manual operation under no-load conditions to verify mechanism integrity and to permit safe maintenance.
+## Transition Type {toc}
−## Manual operation shall be possible only when both sources are de-energized or as otherwise specifically permitted by the listing.
+### The transition type shall be as indicated in the datasheet.
−## The manual operation handle or tool shall be stored with the equipment.
−
−# Auxiliary Contacts {toc}
−
−## The auxiliary contacts furnished shall be as indicated in the datasheet.
−
```datasheet
−label: Auxiliary Contacts
−type: checkbox
+label: Transition Type
+type: radio
options:
− - "Normal position indicating (NO + NC)"
− - "Emergency position indicating (NO + NC)"
− - "Pre-transfer signal (programmable)"
− - "Loss-of-normal signal"
− - "Loss-of-emergency signal"
− - "Not in automatic mode signal"
−default:
− - "Normal position indicating (NO + NC)"
− - "Emergency position indicating (NO + NC)"
+ - "Open transition"
+ - "Delayed transition with a programmed center-off dwell"
+ - "Closed transition with a momentary parallel"
+ - "Closed transition with soft loading"
+default: "Open transition"
```
−## The transfer switch shall be provided with auxiliary contacts indicating position (connected to normal, connected to emergency) for use by remote monitoring, building automation, and load shed systems.
+### The transition type is decided by the load's tolerance of a momentary interruption, by the motor content of the load, and by whether the serving utility will permit the alternate source to be paralleled with its system, and no one type is the norm across projects. {note}
−## A minimum of two normally open and two normally closed contacts on each position shall be wired to terminal blocks accessible without exposing energized parts.
+### Open transition breaks the connection to the source carrying the load before making the connection to the other, so the load is de-energized for the mechanism's transfer time, which is a few cycles on a contactor-type mechanism; equipment with stored energy, including motors, contactors, and electronic power supplies, rides through or drops out according to its own hold-up. {note}
−# Transfer Type {toc}
+### Delayed transition is open transition with a programmed dwell in the center-off position, during which the residual voltage on motor loads decays before the other source is connected; where a motor is reconnected while its residual voltage is still high and out of phase with the new source, the resulting torque transient and inrush can trip breakers and damage couplings, and the dwell is what removes that condition. {note}
−## The transfer type defines how the load is moved between sources and shall be selected based on the load's tolerance to a momentary interruption and on whether the alternate source will be operated in parallel with the normal source during transfer.
+### Closed transition with a momentary parallel connects the alternate source before disconnecting the normal source, for an interval short enough that the two sources are paralleled for a fraction of a second, so the load sees no interruption on a transfer made while both sources are available; a transfer made because the normal source has failed is still an open or delayed transfer, because there is nothing to parallel with. {note}
−## Transfer Type Selection {toc}
+### Soft loading is closed transition in which the parallel is held for several seconds while the controller ramps the real and reactive load from one source to the other, so the load sees no step change in voltage or frequency; it is used where a momentary-parallel transfer would still disturb a sensitive process or a health care load, and it depends on a generator governor and voltage regulator that accept load-sharing control and on the utility's approval of an extended parallel. {note}
−### The transfer type shall be as indicated in the datasheet.
+### Where the datasheet selects a delayed transition, the center-off dwell shall be programmable at the controller and shall be set under this standard.
−```datasheet
−label: Transfer Type
−type: radio
−options:
− - "Open transition (break-before-make)"
− - "Delayed transition (open with programmed neutral time)"
− - "Closed transition (overlapping, ≤100 ms parallel)"
− - "Soft-loading (closed transition with ramped load transfer)"
−default: "Open transition (break-before-make)"
−```
+### Where the datasheet selects a closed transition or soft loading, the controller shall verify that the two sources are within its programmed voltage, frequency, and phase-angle windows before closing the parallel, and shall not close the parallel while any window is unsatisfied.
−## Open Transition {toc}
+### Where the datasheet selects a closed transition or soft loading, the controller shall fall back automatically to an open or delayed transition when the sources cannot be brought within the windows in the programmed time, or when the normal source is lost.
−### Open-transition transfer breaks the connection to one source before making the connection to the other. {note}
+### Where the datasheet selects a closed transition or soft loading, the Contractor shall obtain the serving utility's written approval of parallel operation, including any protective relaying, anti-islanding, and metering provisions the utility requires under its interconnection rules and IEEE 1547, before the switch is released for manufacture.
−### During open-transition transfer the load is briefly de-energized — typically less than 0.1 seconds for a contactor-based mechanism — and equipment with internal energy storage (motors, contactors, lighting ballasts) experiences a momentary loss of voltage. {note}
+### The maximum duration of the momentary parallel shall be as indicated in the datasheet.
−### Open transition is the default and the appropriate selection for the large majority of emergency and standby applications, because it does not require any coordination, parallel-operation permission, or relaying with the utility. {note}
+```datasheet
+label: Momentary Parallel Duration Limit
+type: range
+unit: ms
+derived: "the maximum parallel duration the serving utility's written approval of parallel operation permits"
+options:
+ min: 20
+ max: 1000
+ setpoints: [20, 50, 100, 150, 200, 500, 1000]
+default: derived
+```
−## Delayed Transition {toc}
+### The soft-load ramp duration shall be as indicated in the datasheet.
−### Delayed transition is open transition with a programmable time delay in the neutral (off) position between sources, allowing residual voltage on motor loads to decay before connection to the alternate source, which prevents out-of-phase reclosing on motors and the resulting torque transients and breaker trips. {note}
+```datasheet
+label: Soft-Load Ramp Duration
+type: range
+unit: s
+options:
+ min: 1
+ max: 60
+ setpoints: [1, 2, 5, 10, 20, 30, 60]
+```
−### Delayed transition shall be specified where the load includes significant motor content or where motor in-rush following retransfer has historically tripped breakers or damaged equipment.
+### A momentary parallel of a few cycles is commonly treated by utilities as not constituting interconnection, and an extended parallel almost always is; the utility's approval is what decides the limit, so the limit is derived from that approval rather than selected. {note}
−### The neutral time is typically programmable from 0 to 60 seconds. {note}
+### The switch shall include an independent protective function that opens the parallel if it exceeds the programmed limit, so that a controller failure during a closed transition cannot leave the alternate source connected to the utility.
−## Closed Transition {toc}
+## Bypass-Isolation Construction {toc}
−### Closed-transition transfer briefly parallels the two sources (typically for less than 100 ms) so that the load is never de-energized during retransfer. {note}
+### Whether bypass-isolation construction is furnished shall be as indicated in the datasheet.
−### Closed-transition operation requires that the alternate source be synchronized to the normal source (matched in voltage, frequency, and phase angle) before the transfer is initiated, and requires the explicit permission of the serving utility because the on-site generator is, for a brief interval, paralleled with the utility.
+```datasheet
+label: Bypass-Isolation Construction
+type: radio
+options:
+ - "Not furnished"
+ - "Furnished"
+default: "Not furnished"
+```
−### Closed transition shall not be assumed without confirmed utility approval.
+### Bypass-isolation construction adds a manually operated bypass mechanism that carries the load directly from either source while the automatic mechanism is isolated from both sources and from the load, so the automatic mechanism can be inspected, tested, or replaced without an outage on the load. It adds substantially to the size, weight, and cost of the switch, and it is used where the load cannot accept the planned outage that servicing a switch without bypass requires, which is the condition in a health care essential electrical system, a data center, and a continuous process. {note}
−### The Contractor shall obtain written interconnection approval and shall coordinate any required protective relaying, anti-islanding protection, and metering with the utility before procurement.
+### Where the switch serves a health care essential electrical system branch, the bypass-isolation provision shall be as selected under [[sync/healthcare-essential-electrical-systems]].
−### The closed-transition window shall be set so that the parallel interval is consistent with the utility's approval — typically 100 ms or less.
+### Where bypass-isolation construction is furnished, the bypass mechanism shall be capable of carrying the load from either source, and the isolation mechanism shall provide a test position in which the automatic mechanism can be operated electrically with its load terminals disconnected.
−### If the alternate source cannot be synchronized within the controller's permitted window, the controller shall fall back to open or delayed transition automatically.
+### Where bypass-isolation construction is furnished, the bypass and isolation operations shall be performed by one qualified person from the front of the enclosure without tools other than the operating handles furnished, and without de-energizing the load.
−## Soft-Loading (Closed Transition with Ramped Transfer) {toc}
+### Where bypass-isolation construction is furnished, the bypass mechanism shall be interlocked so that it cannot connect a source to the load that the automatic mechanism is not connected to, unless the automatic mechanism is first isolated.
−### Soft-loading is closed-transition operation in which the controller actively ramps the real and reactive load between the two sources over several seconds while they are paralleled, minimizing voltage and frequency transients on the load, and is appropriate for sensitive process or healthcare applications. {note}
+### Where bypass-isolation construction is furnished, the automatic mechanism shall be withdrawable or removable for replacement while the bypass carries the load.
−### Soft-loading requires more sophisticated generator controls (typically isochronous load sharing with utility interface) and additional utility approval beyond simple closed-transition operation.
+## Neutral Treatment {toc}
−# Pole Configuration {toc}
+### The neutral treatment of the switch shall be as indicated in the datasheet.
−## The transfer switch's pole configuration shall be selected based on whether the alternate source is a separately derived system per NEC 250.30 and on whether the neutral is switched.
−
−## Pole Configuration Selection {toc}
−
−### The pole configuration shall be as indicated in the datasheet.
−
```datasheet
−label: Pole Configuration
+label: Neutral Treatment
type: radio
options:
− - "3-pole (solid neutral, neutral not switched)"
− - "4-pole (switched neutral, fully separated)"
− - "3-pole with overlapping neutral (where listed)"
−default: "4-pole (switched neutral, fully separated)"
+ - "No neutral pole, three-wire system"
+ - "Solid neutral, not switched"
+ - "Switched neutral"
+ - "Switched neutral with overlapping contacts"
```
−## 3-Pole (Solid Neutral) {toc}
+### The neutral treatment decides whether the alternate source is a separately derived system, and it is the single selection under this standard that reaches the grounding of the generator; it is stated here because the number of poles is bought with the switch, and it is confirmed against the generator neutral bonding selected under [[sync/generators]] and the separately derived system provisions of [[sync/grounding-and-bonding]]. {note}
−### A 3-pole transfer switch switches the three phase conductors only; the neutral passes through unbroken and is solidly connected between the normal source neutral, the load neutral, and the alternate source neutral. {note}
+### With a solid neutral the neutral conductor passes through the switch unbroken, the alternate source is not a separately derived system, and the service main bonding jumper is the single neutral-to-ground bond for both sources; with a switched neutral the neutral is transferred with the phase conductors, the alternate source is a separately derived system under NEC 250.30, and the alternate source carries its own system bonding jumper and grounding electrode connection. {note}
−### With a 3-pole ATS, the alternate source (generator) is not a separately derived system — the service main bonding jumper at the utility service is the single neutral-to-ground bond, and no system bonding jumper is installed at the generator. {note}
+### Where the neutral is solid and the alternate source is also bonded to ground at its own neutral, neutral current divides between the neutral conductor and the equipment grounding path, which places objectionable current on the grounding conductors and defeats the ground-fault sensing on the service; where the neutral is switched and the alternate source is not bonded, the load has no ground reference while it is on the alternate source. Either mismatch is a wiring error, and the neutral treatment and the generator bonding are checked together. {note}
−### The 3-pole arrangement is mechanically simpler and is acceptable for many smaller and non-critical applications, but it requires the generator neutral to be bonded only at the service main and not at the generator itself.
+### Where ground-fault protection is provided on the alternate source, or where ground-fault indication is provided at the alternate source in accordance with NEC 700.31, the neutral shall be switched, because a residual sensor at a source that is not separately derived does not see the fault current that returns through the service bonding jumper.
−## 4-Pole (Switched Neutral) {toc}
+### Where the datasheet selects a switched neutral, the alternate source shall be bonded and grounded as a separately derived system in accordance with NEC 250.30 and [[sync/grounding-and-bonding]], and the system bonding jumper shall exist at one point only.
−### A 4-pole transfer switch switches the neutral together with the three phase conductors. {note}
+### Where the datasheet selects a solid neutral, the alternate source shall not be bonded to ground at its neutral, and the Contractor shall confirm the absence of a neutral-to-ground bond at the alternate source before the switch is energized.
−### With a 4-pole ATS, the alternate source becomes a separately derived system per NEC 250.30, and a system bonding jumper shall be installed at the generator (or at the first system disconnecting means on the generator side) and shall not be installed in parallel with the service main bonding jumper.
+### A switched neutral without overlapping contacts opens the load neutral for the duration of the transfer, and on a four-wire load that is unbalanced across its phases the line-to-neutral voltages shift during that interval; overlapping neutral contacts make the neutral connection to the new source before breaking it from the old one, so the load neutral is never open. {note}
−### The 4-pole arrangement isolates the load neutral from the normal source neutral when running on the alternate source, which eliminates ground-fault sensing confusion, prevents objectionable neutral currents on grounding conductors, and is the default for systems with ground-fault protection on either or both sources. {note}
+### Where the datasheet selects a switched neutral with overlapping contacts, the overlap shall be listed under UL 1008 for the switch, and the neutral pole shall be rated for the full continuous current of the switch.
−### A 4-pole switch shall be specified where the system has ground-fault protection per NEC 230.95 (most services 1000A and larger at 480/277V), where multiple service mains feed the same load through transfer switches, and where the design requires the generator to be a separately derived system.
+## Manual Operation {toc}
−### When in doubt, 4-pole is the safer default. {note}
+### The switch shall be furnished with a manual operator that transfers the mechanism between sources with the controller disconnected, for maintenance and for verification of mechanical operation.
−### The Contractor shall coordinate the resulting system bonding jumper and grounding electrode connection at the generator with [[sync/grounding-and-bonding]] and [[sync/generators]].
+### Manual operation with a source energized shall be performed only where the listing covers manual operation under that condition, and the enclosure shall carry the manufacturer's instruction stating the condition under which the manual operator may be used.
−## Overlapping Neutral {toc}
+### The manual operator or its detachable handle shall be stored inside the enclosure or in a holder fixed to the enclosure exterior.
−### Some listed transfer switches provide an overlapping neutral — a neutral pole that makes the alternate connection before breaking the original connection — to avoid a momentarily open neutral during transfer. {note}
+## Auxiliary Contacts {toc}
−### An open neutral on a 4-pole transfer of an unbalanced load can cause line-to-neutral voltage excursions on the load. {note}
+### The auxiliary contacts furnished on the switch shall be as indicated in the datasheet.
−### Overlapping neutral construction prevents open-neutral voltage excursions and shall be considered for 4-pole switches feeding heavily unbalanced single-phase loads.
−
−# Bypass-Isolation {toc}
−
−## Bypass-isolation transfer switches add a manually operated bypass mechanism that allows the load to be carried directly from either source while the automatic transfer mechanism is electrically isolated and physically removed from the live bus for inspection, testing, or replacement.
−
−## Bypass-Isolation Selection {toc}
−
−### Whether bypass-isolation construction is furnished shall be as indicated in the datasheet.
−
```datasheet
−label: Bypass-Isolation
−type: radio
+label: Auxiliary Contacts
+type: checkbox
options:
− - "Not required (standard automatic transfer switch)"
− - "Bypass-isolation construction (no-load interruption during maintenance)"
−default: "Not required (standard automatic transfer switch)"
+ - "Switch connected to the normal source"
+ - "Switch connected to the alternate source"
+ - "Normal source available"
+ - "Alternate source available"
+ - "Controller not in automatic mode"
+ - "Pre-transfer signal"
+ - "Load-shed active"
+ - "Bypass mechanism not in the automatic position"
+default:
+ - "Switch connected to the normal source"
+ - "Switch connected to the alternate source"
+ - "Normal source available"
+ - "Alternate source available"
```
−## Bypass-Isolation Application {toc}
+### Each selected position contact shall be furnished as not fewer than two normally open and two normally closed contacts, and every auxiliary contact shall be wired to terminal blocks that can be reached without exposing energized power conductors.
−### Bypass-isolation construction shall be specified where continuity of operation cannot tolerate the planned outage that would be required to service a non-bypass switch.
+### Auxiliary contacts shall be rated for the pilot duty of the circuit they serve, and shall be isolated from the controller's own logic so that a fault on an external circuit cannot disable the controller.
−### Typical applications include hospital essential electrical systems, data centers, critical industrial processes, telecommunications central offices, and other facilities operating under NFPA 110 Level 1 with strict outage limits. {note}
−
−### Bypass-isolation construction adds substantial size, weight, and cost; it should not be selected by default but where it is justified by the load criticality.
−
−### The bypass operation shall be capable of being performed by a single qualified person without specialized tools and shall not require de-energizing the load.
−
# Controller {toc}
−## The transfer switch controller shall be microprocessor-based, with a non-volatile memory retaining all settings and event logs across power outages.
+## Controller Construction {toc}
−## The controller shall provide voltage and frequency sensing on both sources, programmable time delays, manual and automatic transfer modes, an exerciser clock, an event log, and a local human-machine interface.
+### The controller shall be microprocessor based, shall retain every setting and the event log in non-volatile memory through loss of both sources, and shall be powered from both sources with automatic selection so that it remains operable whenever either source is present.
−## Controller Display {toc}
+### The controller shall provide automatic operation, a test mode that simulates loss of the normal source with and without load transfer, an event log recording each source condition change and each transfer with a time stamp, and a local interface at which every setting can be read and changed.
+### Changes to settings at the local interface shall be protected by a password or a keyed switch so that a setting cannot be changed by an unauthorized person.
+
### The controller display shall be as indicated in the datasheet.
…2 unchanged lines
type: select
options:
− - "Alphanumeric LCD with status LEDs"
− - "Graphical LCD with menu navigation"
+ - "Alphanumeric display with status indicators"
+ - "Graphical display with menu navigation"
- "Color touchscreen"
default: manufacturer
```
−### The display type does not affect the transfer function, and every listed controller provides local status and setting access, so the manufacturer's standard display is acceptable unless the Owner's operations program calls for a specific interface. {note}
+### The display does not affect the transfer function, and every listed controller gives local access to status and settings, so the manufacturer's offering is acceptable unless the Owner's operating program calls for one interface across its equipment. {note}
+### Where the switch serves a system classified under NFPA 110, the controller shall provide every transfer switch function NFPA 110 Section 6.2 requires for that level, including a time delay on engine start, a time delay on transfer, an adjustable time delay on retransfer, a bypass of the retransfer delay on failure of the alternate source, a time delay for unloaded running of the alternate source, a test switch, and an exerciser.
+
## Source Sensing {toc}
### The source sensing functions provided by the controller shall be as indicated in the datasheet.
```datasheet
−label: Source Sensing
+label: Source Sensing Functions
type: checkbox
options:
− - "Three-phase under-voltage on normal"
− - "Three-phase over-voltage on normal"
− - "Phase loss / single-phase on normal"
− - "Phase rotation / phase reversal on normal"
− - "Under-frequency on alternate"
− - "Over-frequency on alternate"
− - "Phase angle / synchronization for closed transition"
+ - "Undervoltage on each phase of the normal source"
+ - "Overvoltage on each phase of the normal source"
+ - "Phase loss on the normal source"
+ - "Phase rotation on the normal source"
+ - "Voltage unbalance on the normal source"
+ - "Undervoltage on each phase of the alternate source"
+ - "Overvoltage on the alternate source"
+ - "Underfrequency on the alternate source"
+ - "Overfrequency on the alternate source"
+ - "Underfrequency and overfrequency on the normal source"
+ - "Phase angle between sources"
default:
− - "Three-phase under-voltage on normal"
− - "Three-phase over-voltage on normal"
− - "Phase loss / single-phase on normal"
− - "Under-frequency on alternate"
− - "Over-frequency on alternate"
+ - "Undervoltage on each phase of the normal source"
+ - "Overvoltage on each phase of the normal source"
+ - "Phase loss on the normal source"
+ - "Undervoltage on each phase of the alternate source"
+ - "Underfrequency on the alternate source"
+ - "Overfrequency on the alternate source"
```
−### The controller shall sense voltage on all phases of both the normal and alternate sources and shall sense frequency on the alternate source.
+### The controller shall sense voltage on every phase of both sources, and shall sense frequency on the alternate source, so that a single-phase failure on the normal source and an unstable alternate source are both detected before the load is affected.
−### Pickup and dropout setpoints for voltage and frequency shall be independently programmable.
+### Each sensing function shall have independently programmable pickup and dropout set points with hysteresis between them, so that a transient near the set point does not cycle the switch.
−### The controller shall initiate engine start on under-voltage, over-voltage, under-frequency, over-frequency, or phase loss on the normal source, with each condition independently enabled or disabled.
+### Where the datasheet selects a closed transition or soft loading, the phase-angle sensing function shall be furnished.
−### Voltage sensing shall include both pickup and dropout setpoints (with hysteresis) to prevent nuisance transfers from short transients.
+### The undervoltage dropout set point on the normal source shall be as indicated in the datasheet.
−### Frequency sensing shall be applied to the alternate source to confirm the generator has reached operating frequency before transfer.
−
−## In-Phase Monitor {toc}
−
−### Whether an in-phase monitor is provided shall be as indicated in the datasheet.
−
```datasheet
−label: In-Phase Monitor
−type: radio
+label: Normal Source Undervoltage Dropout Set Point
+type: range
+unit: '% of nominal'
options:
− - "Not provided"
− - "Provided, programmable phase window"
+ min: 70
+ max: 95
+ setpoints: [70, 75, 80, 85, 90, 95]
```
−### For open-transition or delayed-transition transfer of motor loads, the controller may provide an in-phase monitor that delays retransfer until the two sources are within a programmed phase angle window.
+### The undervoltage pickup set point on the normal source shall be as indicated in the datasheet.
−### The in-phase monitor reduces motor torque transients on retransfer without requiring synchronization or closed-transition operation, and is appropriate for motor-dominated loads (elevators, large pumps, compressors). {note}
−
−## Exerciser Clock {toc}
−
−### The exerciser schedule shall be as indicated in the datasheet.
−
```datasheet
−label: Exerciser Schedule
−type: select
+label: Normal Source Undervoltage Pickup Set Point
+type: range
+unit: '% of nominal'
options:
− - "Weekly, no load (controller starts generator, does not transfer load)"
− - "Weekly, with load transfer"
− - "Monthly, with load transfer (NFPA 110 Level 1 minimum)"
− - "Custom schedule established by the Engineer"
−default: "Monthly, with load transfer (NFPA 110 Level 1 minimum)"
+ min: 80
+ max: 100
+ setpoints: [80, 85, 90, 95, 100]
```
−### The controller shall include a programmable exerciser that starts the alternate source on a scheduled basis to confirm readiness and to exercise the generator and its fuel system.
+### Where a sensing set point is not selected in the datasheet, the manufacturer's factory setting shall apply as the initial setting, and its value shall be recorded on the settings record submitted for review.
−### NFPA 110 Level 1 systems require a monthly exercise of at least 30 minutes under load or per the manufacturer's recommended test cycle.
+### A dropout set near nominal starts the alternate source on a voltage sag that the load would have ridden through, which costs engine starts and fuel; a dropout set low leaves the load on a source that is browning out, which is the condition that damages motors and electronic power supplies. The pickup sits above the dropout by the hysteresis the sensing needs to settle. {note}
−### NFPA 110 Level 2 systems and NEC Article 700/701 systems have similar but not identical exercise requirements that shall govern.
+## In-Phase Monitor {toc}
−## Load Shed and Priority {toc}
+### Whether an in-phase monitor is furnished shall be as indicated in the datasheet.
−### The load-shed and source-priority provisions shall be as indicated in the datasheet.
−
```datasheet
−label: Load Shed / Source Priority
+label: In-Phase Monitor
type: radio
options:
− - "Not required (generator sized for full load)"
− - "Programmable load-shed outputs"
− - "Source priority coordination across multiple ATS"
−default: "Not required (generator sized for full load)"
+ - "Not furnished"
+ - "Furnished"
```
−### Where the alternate source has insufficient capacity to carry the entire load, the controller shall provide load-shed outputs to drop non-critical loads in a programmable sequence as the generator approaches capacity, and load-add outputs to restore them as capacity allows.
+### An in-phase monitor holds an open-transition transfer until the two sources drift into a programmed phase-angle window and then releases it, so a motor is reconnected close to in phase without a center-off dwell and without synchronizing control; where the load is dominated by motors on an open-transition switch, it removes the out-of-phase reconnection transient that a delayed transition removes by waiting, at the cost of a transfer that waits for the sources to align rather than proceeding at once. {note}
−### Where multiple transfer switches share a single alternate source, the controllers shall coordinate source priority so that critical switches transfer first and non-critical switches wait for capacity.
+### Where the datasheet furnishes an in-phase monitor, its phase-angle window shall be programmable, and the controller shall complete the transfer without waiting for the window when the source carrying the load has failed.
−### The Contractor shall coordinate load-shed strategy with [[sync/generators]] and the load calculations.
+## Time Delays {toc}
−# Time Delays {toc}
+### Each time delay in this article shall be independently programmable at the controller across the full range indicated for it, and the value at which each is set shall be recorded on the settings record.
−## The transfer switch controller shall provide independently programmable time delays for each transfer event.
+### The time delay on engine start shall be as indicated in the datasheet.
−## The defaults specified in each time-delay section reflect typical NFPA 110 Level 1 settings and shall be adjusted to suit the project; the final values shall be recorded in the commissioning report.
−
−## Time-Delay Engine Start (TDES) {toc}
−
−### The TDES setting shall be as indicated in the datasheet.
−
```datasheet
−label: Time-Delay Engine Start (TDES)
+label: Time Delay on Engine Start
type: range
unit: s
options:
min: 0
max: 30
− setpoints: [0, 1, 3, 5, 10, 30]
−default: 3
+ setpoints: [0, 0.5, 1, 2, 3, 5, 10, 15, 30]
```
−### TDES is the time the controller waits after detecting a loss of normal source before signaling the generator to start. {note}
+### The engine-start delay is the interval between the controller detecting a normal source failure and the engine-start signal, and it exists so that a momentary utility disturbance does not start the engine; every second of it counts against the restoration time the article the switch serves allows. {note}
−### A short TDES (1 to 5 seconds) prevents nuisance starts from very brief utility disturbances while still complying with the 10-second start requirement of NFPA 110 Level 1. {note}
+### The time delay on transfer to the alternate source shall be as indicated in the datasheet.
−### For Type 10 systems, total time from loss-of-normal to load-on-emergency shall not exceed 10 seconds.
+```datasheet
+label: Time Delay on Transfer to the Alternate Source
+type: range
+unit: s
+options:
+ min: 0
+ max: 300
+ setpoints: [0, 1, 2, 3, 5, 10, 30, 60, 120, 300]
+```
−## Time-Delay Transfer to Emergency (TDTE) {toc}
+### The transfer delay runs after the alternate source is within its voltage and frequency windows and before the load is connected, so that a source that has only momentarily reached its window is not loaded; a longer delay is used where several switches share one alternate source and the loads are picked up in a sequence, in which case the delay is the staggering mechanism. {note}
−### The TDTE setting shall be as indicated in the datasheet.
+### The time delay on retransfer to the normal source shall be as indicated in the datasheet.
```datasheet
−label: Time-Delay Transfer to Emergency (TDTE)
+label: Time Delay on Retransfer to the Normal Source
type: range
−unit: s
+unit: min
options:
min: 0
max: 60
− setpoints: [0, 1, 3, 5, 10, 60]
−default: 1
+ setpoints: [0, 1, 2, 5, 10, 15, 30, 60]
```
−### TDTE is the time the controller waits, after the alternate source is stable, before transferring the load. {note}
+### The retransfer delay runs after the normal source returns within its windows and before the load is returned to it, so that a utility restoration that collapses again within minutes does not cycle the load between sources. {note}
−### A short delay (1 to 3 seconds) confirms the alternate source has stabilized; longer delays may be appropriate where the generator is shared with other transfer switches and load shedding must occur first.
+### The retransfer delay shall be bypassed automatically when the alternate source fails while carrying the load, so that the load is returned to an available normal source without waiting.
−## Time-Delay Retransfer to Normal (TDRN) {toc}
+### The time delay for unloaded running of the alternate source shall be as indicated in the datasheet.
−### The TDRN setting shall be as indicated in the datasheet.
−
```datasheet
−label: Time-Delay Retransfer to Normal (TDRN)
+label: Time Delay for Unloaded Running of the Alternate Source
type: range
unit: min
+derived: "the unloaded cool-down run time the generator manufacturer publishes for the set furnished under the generator standard"
options:
min: 0
max: 30
− setpoints: [0, 1, 5, 10, 15, 30]
−default: 15
+ setpoints: [0, 1, 2, 5, 10, 15, 30]
+default: derived
```
−### TDRN is the time the controller waits, after the normal source is restored and stable, before retransferring the load. {note}
+### The unloaded running delay keeps the engine running after the load has been retransferred so that the engine cools under controlled conditions, and its value is a property of the engine rather than of the switch. {note}
−### A long retransfer delay (typically 10 to 30 minutes) confirms that the utility restoration is stable and avoids cycling the generator and the load on a marginal utility recovery; NFPA 110 commentary recommends 30 minutes for stable utility verification. {note}
+### The center-off dwell for a delayed transition shall be as indicated in the datasheet.
−## Time-Delay Engine Cool-Down (TDEC) {toc}
−
−### The TDEC setting shall be as indicated in the datasheet.
−
```datasheet
−label: Time-Delay Engine Cool-Down (TDEC)
+label: Delayed Transition Center-Off Dwell
type: range
−unit: min
+unit: s
options:
min: 0
− max: 30
− setpoints: [0, 5, 10, 15, 30]
−default: manufacturer
+ max: 120
+ setpoints: [0, 0.5, 1, 2, 3, 5, 10, 30, 60, 120]
```
−### TDEC is the time the generator runs unloaded after the load is retransferred to normal, to allow controlled cool-down of the engine. {note}
+### The dwell is set to the time the residual voltage of the connected motors takes to decay to a level the new source can be connected against, which is a property of the motor inertia and the loads on the shafts rather than of the switch; the dwell applies only where the datasheet selects a delayed transition, and is otherwise without effect. {note}
−### The required TDEC value is set by the generator manufacturer and shall be coordinated with [[sync/generators]].
+### Where a time delay is not selected in the datasheet, the manufacturer's factory setting shall apply as the initial setting, and its value shall be recorded on the settings record submitted for review.
−### Skipping cool-down shortens engine life. {note}
+### Where the switch serves an Article 700 emergency system, the sum of the engine-start delay, the alternate source's start and stabilization time, and the transfer delay shall not exceed 10 seconds, in accordance with NEC 700.12.
−## Time-Delay Neutral (TDN) {toc}
+### Where the switch serves an Article 701 legally required standby system, the same sum shall not exceed 60 seconds, in accordance with NEC 701.12.
−### The TDN setting shall be as indicated in the datasheet.
+## Exerciser {toc}
+### The controller shall include an exerciser that starts the alternate source on a programmed schedule, with the schedule retained through loss of both sources.
+
+### The exercise interval shall be as indicated in the datasheet.
+
```datasheet
−label: Time-Delay Neutral (TDN)
+label: Exercise Interval
type: range
−unit: s
+unit: days
options:
− min: 0
− max: 60
− setpoints: [0, 1, 3, 5, 10, 60]
−default: 3
+ min: 7
+ max: 90
+ setpoints: [7, 14, 30, 60, 90]
```
−### TDN applies only where delayed transition is selected; it is the time the load is intentionally held in the neutral (off) position during a delayed-transition transfer, to allow motor residual voltage to decay before connection to the new source. {note}
+### The exercise period shall be as indicated in the datasheet.
−### TDN shall be set based on the motor decay characteristics of the load; 1 to 5 seconds is typical for general-purpose motors.
+```datasheet
+label: Exercise Period
+type: range
+unit: min
+options:
+ min: 5
+ max: 120
+ setpoints: [5, 10, 15, 30, 60, 120]
+```
−# Engine Start Contacts {toc}
+### Whether the load is transferred to the alternate source during the exercise shall be as indicated in the datasheet.
−## The transfer switch shall provide dry, isolated contacts to start the engine-generator.
+```datasheet
+label: Load Transfer During Exercise
+type: radio
+options:
+ - "Alternate source started and run without transferring the load"
+ - "Load transferred to the alternate source for the exercise period"
+```
−## Two contacts shall be furnished: a normally closed contact that opens to call for start on loss of normal source (the standard engine-start contact), and an additional normally open contact for use by the generator controller's manual remote-start or test inputs as required.
+### An exercise without load transfer proves that the engine starts and runs, and nothing else; an exercise under load proves the transfer, the retransfer, and the engine's ability to carry the building, at the cost of an interruption to the load at each transfer on an open-transition switch. {note}
−## Contacts shall be rated for the generator starting circuit voltage (typically 12 or 24 VDC) and shall be wired to terminal blocks accessible without removing the controller.
+### Where the switch serves a system classified under NFPA 110, the exercise interval, the exercise period, and the load carried shall satisfy NFPA 110 Section 8.4 for the engine type, and the exerciser shall be set so that those tests occur without operator action.
−## Engine Start Wiring {toc}
+### The exerciser shall be programmable for the day of the week and the time of day, and shall be capable of being set for the interval and period selected in the datasheet.
+## Load Management {toc}
+
+### The load-management provisions furnished shall be as indicated in the datasheet.
+
```datasheet
−label: Engine Start Wiring
+label: Load Management Provisions
+type: checkbox
+options:
+ - "Load-shed input that retransfers the switch or opens it on an external signal"
+ - "Programmable transfer delay to stagger load pickup among switches sharing one alternate source"
+ - "Elevator pre-transfer signal with programmable delay"
+ - "Load-shed output contacts to drop downstream loads before transfer"
+```
+
+### Where the alternate source cannot carry the entire load of every switch connected to it, the switches serving the lower-priority loads are held off or shed so that the source is not overloaded at pickup; which mechanism does that, and in what order, is fixed at the system level under [[sync/emergency-and-standby-power]] and configured at each switch. {note}
+
+### Where a load-shed input is furnished, the switch shall act on the external signal within the time the system design requires, and shall restore the load automatically when the signal is removed unless the datasheet or the system design requires manual restoration.
+
+### Where an elevator pre-transfer signal is furnished, the signal shall be given before every transfer in both directions, and the delay between the signal and the transfer shall be programmable so that the elevator controller can bring the car to a landing.
+
+### The Contractor shall set the load-management provisions of every switch on the project to the sequence established under [[sync/emergency-and-standby-power]] and shall demonstrate that sequence during the integrated system test.
+
+## Engine-Start Contacts {toc}
+
+### The engine-start wiring arrangement shall be as indicated in the datasheet.
+
+```datasheet
+label: Engine-Start Wiring Arrangement
type: radio
options:
− - "Two-wire start (single contact closure)"
− - "Three-wire start with separate run signal"
−default: "Two-wire start (single contact closure)"
+ - "Two-wire start"
+ - "Three-wire start"
+default: "Two-wire start"
```
−### Engine start wiring shall be installed between the transfer switch and the generator in dedicated raceway, separated from power conductors where required by NEC 700.10(D) for emergency systems.
+### A two-wire start is a single contact that closes to call for the engine and opens to release it, and it is the arrangement every current generator controller accepts; a three-wire start uses separate start and stop signals and is furnished to match an existing generator controller that needs it. {note}
−### The Contractor shall coordinate raceway and conductor types with [[sync/conductors-and-cables]].
+### The switch shall provide dry, isolated engine-start contacts, rated for the voltage and current of the generator control circuit, wired to terminal blocks that can be reached without removing the controller.
−# Communications {toc}
+### The engine-start contact shall be arranged so that loss of control power at the switch calls for the engine to start.
−## The transfer switch controller shall provide communications appropriate to the project's monitoring and building management integration requirements.
+### Where the switch serves an Article 700 emergency system, the engine-start wiring between the switch and the alternate source shall be installed and separated in accordance with NEC 700.10, and where an Article 701 system, in accordance with NEC 701.10.
−## Communications Interface {toc}
+## Communications {toc}
−### The communications interfaces provided at the transfer switch shall be as indicated in the datasheet.
+### The communications interfaces furnished at the switch shall be as indicated in the datasheet.
```datasheet
−label: Communications Interface
+label: Communications Interfaces
type: checkbox
options:
− - "Dry contacts, no protocol"
− - "Modbus RTU (RS-485)"
− - "Modbus TCP/IP (Ethernet)"
− - "BACnet IP"
+ - "Dry contacts only"
+ - "Modbus RTU serial"
+ - "Modbus TCP"
+ - "BACnet MS/TP"
+ - "BACnet/IP"
- "SNMP"
− - "Manufacturer's proprietary protocol over Ethernet"
+ - "Proprietary protocol over Ethernet"
```
−### The protocol follows from the building automation or monitoring platform the project actually uses, so the field carries no default. {note}
+### The protocol follows from the monitoring platform the project uses, so the field carries no default; dry contacts are listed so that a switch reporting only through its auxiliary contacts is recorded as such rather than left blank. {note}
−### Whether a remote annunciator is provided shall be as indicated in the datasheet.
+### Where a protocol interface is furnished, the switch shall report at least its position, the availability of each source, its automatic or non-automatic mode, the active time delay, the exerciser status, and each event in its log, and the point list shall be coordinated with [[sync/building-automation-system]].
+### Where a remote annunciator is furnished under [[sync/generators]], the position and source-available contacts selected in the datasheet shall be wired to it, and the annunciator shall be tested together with the switch.
+
+# Enclosure {toc}
+
+## Enclosure Type {toc}
+
+### The enclosure type shall be as indicated in the datasheet.
+
```datasheet
−label: Remote Annunciator (NFPA 110 Level 1)
−type: radio
+label: Enclosure Type
+type: select
options:
− - "Not required"
− - "Provided per NFPA 110 §5.6.5"
+ - "NEMA Type 1"
+ - "NEMA Type 2"
+ - "NEMA Type 3R"
+ - "NEMA Type 4"
+ - "NEMA Type 4X"
+ - "NEMA Type 12"
+default: "NEMA Type 1"
```
−### Whether a remote annunciator is required follows from the NFPA 110 level and the NEC article the system is designed to, so the field carries no default. {note}
+### A dry, conditioned electrical room is the installed location on most projects, which is why Type 1 is the default; every other location named in the clauses of this article calls for the type those clauses require. {note}
−### Where the project includes a building automation system or generator monitoring platform, the transfer switch shall be integrated using the protocol indicated in the datasheet.
+### The enclosure shall comply with NEMA 250 and UL 50E for the type selected, and the type shall be marked on the enclosure.
−### The Contractor shall coordinate with [[sync/building-automation-system]] for the points list, addressing, and network connectivity.
+### A Type 1 enclosure protects against incidental contact and falling dirt only, so it is rated for a dry, conditioned interior location and for nothing wetter or dustier than that. {note}
−### Where remote monitoring is required for NFPA 110 Level 1 systems, the remote alarm annunciator and the transfer switch communications shall be coordinated and tested as a single system.
+### A switch installed outdoors shall have an enclosure of Type 3R, Type 4, or Type 4X.
−# Enclosure {toc}
+### A switch installed where it is subject to hose-directed water or wash-down shall have an enclosure of Type 4 or Type 4X.
−## The transfer switch enclosure shall match the environmental conditions of the installed location and shall comply with NEMA 250 for the rating selected.
+### A switch installed where the atmosphere carries salt, chemical vapor, or another corrosive agent, including a coastal site, a wastewater facility, and a food-processing area, shall have a Type 4X enclosure.
−## Enclosure Rating {toc}
+### A switch installed indoors where airborne dust, lint, or fibers accumulate shall have an enclosure of Type 12, Type 4, or Type 4X.
−### The enclosure rating shall be as indicated in the datasheet.
+### A switch installed indoors where dripping or light splashing of non-corrosive liquid occurs shall have an enclosure of Type 2, Type 12, Type 4, or Type 4X.
+### Where a rating higher than the datasheet selection is required by the clauses of this article for the installed location, the higher rating shall be furnished and the conflict reported to the Engineer of Record before the switch is released for manufacture.
+
+## Enclosure Material and Access {toc}
+
+### The enclosure material shall be as indicated in the datasheet.
+
```datasheet
−label: Enclosure Rating
+label: Enclosure Material
type: select
options:
− - "NEMA 1 — Indoor general purpose"
− - "NEMA 3R — Outdoor rainproof"
− - "NEMA 4 — Indoor/outdoor watertight"
− - "NEMA 4X — Watertight, corrosion-resistant (stainless or non-metallic)"
− - "NEMA 12 — Industrial, dust-tight"
−default: "NEMA 1 — Indoor general purpose"
+ - "Painted steel"
+ - "Type 304 stainless steel"
+ - "Type 316 stainless steel"
+ - "Non-metallic"
```
−### NEMA 1 is appropriate for typical indoor electrical rooms with clean, dry, climate-controlled conditions. {note}
+### Painted steel serves every type in a non-corrosive exposure; stainless steel and non-metallic enclosures are what a Type 4X rating is built in, with Type 316 holding up where chlorides are present and a non-metallic enclosure holding up where the corrodent attacks stainless steel. {note}
−### NEMA 3R is appropriate for outdoor installation in areas not subject to direct wash-down. {note}
+### Where the datasheet selects a Type 4X enclosure, the enclosure material shall be one for which the Type 4X rating is listed.
−### NEMA 4X shall be specified for coastal, chemical, food-processing, or wash-down environments where corrosion resistance is required.
+### The enclosure shall have a hinged front door or doors, with provision for padlocking in the closed position, giving access to the controller, the manual operator, the auxiliary and control terminals, and the bypass-isolation handles where furnished, without exposing energized power conductors.
−### NEMA 12 is appropriate for industrial spaces with significant airborne dust. {note}
+### The power terminals shall be furnished with lugs listed for the conductor material, size, and quantity as indicated on [[drawing: the one-line diagram and the feeder schedule]].
−## Doors, Access, and Conduit Entry {toc}
+### Conduit entry shall be from the top, the bottom, or the side as indicated on [[drawing: the electrical plans]], and the entry area shall be sized for the source and load feeders, the engine-start wiring, and the communications cabling.
+## Mounting Arrangement {toc}
+
### The mounting arrangement shall be as indicated in the datasheet.
```datasheet
−label: Mounting
+label: Mounting Arrangement
type: radio
+drawing_ref: "the electrical plans"
options:
- "Wall mounted"
− - "Floor standing on concrete housekeeping pad"
+ - "Floor standing"
+default: deferred
```
−### Wall mounting shall be limited to frames within the manufacturer's published wall-mount rating; all other frames shall be floor standing.
+### A switch shall be wall mounted only where its frame is within the manufacturer's published wall-mount limit, and every larger frame shall be floor standing.
−### The enclosure shall include hinged front access doors with provisions for padlocking in the closed position.
−
−### Doors shall provide access to the controller display, the manual operation handle, and the maintenance terminals without exposing energized power conductors.
−
−### Provisions for conduit entry shall accommodate the source and load feeders, control wiring to the generator, and communications cabling.
−
−### Conduit entry locations shall be [[drawing: as indicated on the equipment shop drawings]].
−
# Identification and Labeling {toc}
−## Identification of the transfer switch shall follow [[sync/equipment-labeling]] conventions and shall additionally include the items indicated in the datasheet.
+## Field-installed labels shall be provided as indicated in the datasheet and shall comply with [[sync/equipment-labeling]].
```datasheet
−label: Required Identification
+label: Transfer Switch Labeling
type: checkbox
options:
− - "Equipment designation matching one-line diagram"
− - "Normal source identification (panel/switchgear of origin)"
− - "Alternate source identification (generator designation)"
− - "Load identification (loads served)"
− - "UL 1008 listing label visible"
− - "Available fault current and date determined (NEC 110.24)"
− - "Arc flash warning per NFPA 70E"
− - "Service entrance warning (where service entrance rated)"
− - "Emergency system identification (Article 700 systems)"
+ - "Equipment designation matching the one-line diagram"
+ - "Normal source identification"
+ - "Alternate source identification"
+ - "Loads served"
+ - "Available fault current with the calculation date"
+ - "Withstand and closing rating with the upstream device it is based on"
+ - "Arc-flash warning label"
+ - "Emergency system identification"
+ - "Service disconnect identification"
+ - "Bypass-isolation operating sequence"
default:
− - "Equipment designation matching one-line diagram"
− - "Normal source identification (panel/switchgear of origin)"
− - "Alternate source identification (generator designation)"
− - "Load identification (loads served)"
− - "UL 1008 listing label visible"
− - "Available fault current and date determined (NEC 110.24)"
− - "Arc flash warning per NFPA 70E"
+ - "Equipment designation matching the one-line diagram"
+ - "Normal source identification"
+ - "Alternate source identification"
+ - "Loads served"
+ - "Available fault current with the calculation date"
+ - "Withstand and closing rating with the upstream device it is based on"
+ - "Arc-flash warning label"
```
−## The available fault current at service equipment and at the line side of the transfer switch shall be field-marked, including the date of the determination, per NEC 110.24.
+## The available fault current at the switch terminals shall be field-marked with the date of the calculation in accordance with NEC 110.24.
−## Where the transfer switch is in an Article 700 emergency system, the enclosure shall be marked as such per NEC 700.5(C) and 700.10.
+## Where the switch serves an Article 700 or Article 701 system, its withstand and closing rating, together with the upstream overcurrent device type and settings on which that rating is based, shall be field-marked on the exterior of the enclosure in accordance with NEC 700.5(E) or NEC 701.5(D).
−## Labels shall be permanent, weather-resistant where exposed, and legible from the front of the equipment without obstruction.
+## Where the switch serves an Article 700 emergency system, the enclosure shall be marked as a component of the emergency system in accordance with NEC 700.10(A), and the sign NEC 700.7 requires at the service equipment shall identify the switch and the location of the alternate source.
+## The arc-flash warning label shall carry the values established under [[sync/arc-flash-study]] for the switch, and shall be placed so that it is read before the door is opened.
+
+## Labels shall be permanent, resistant to the environment the enclosure type is selected for, and legible from the operating position without removing a cover.
+
# Testing {toc}
−## Factory Tests {toc}
+## Factory Production Tests {toc}
−### The manufacturer shall perform the following production tests on each transfer switch before shipment, with results recorded on a certified test report:
+### The manufacturer shall perform the following production tests on every switch before shipment and shall record the results on a certified test report identified by serial number:
−- Dielectric withstand test per UL 1008
−- Mechanical operation (minimum five complete transfer cycles, normal-to-emergency and emergency-to-normal)
−- Electrical operation of the power switching mechanism and controller, on the rated control voltage
−- Controller functional test, including all programmable time delays, source sensing setpoints, and engine-start contacts
−- Continuity and polarity of all auxiliary contacts and communications terminals
−- Visual and dimensional inspection
+- dielectric withstand test in accordance with UL 1008
+- not fewer than five complete electrically operated transfer cycles in each direction at rated control voltage
+- verification of the mechanical interlock in each position and, where furnished, of the bypass-isolation interlocks through the full operating sequence
+- functional test of the controller, including every time delay, every sensing set point, the exerciser, and the engine-start contacts
+- continuity and operation of every auxiliary contact and every communications output
+- visual and dimensional inspection, including the nameplate against the order
−### Factory acceptance test witnessing shall be as indicated in the datasheet.
+### Factory test witnessing shall be as indicated in the datasheet.
```datasheet
−label: Factory Acceptance Test
+label: Factory Test Witnessing
type: radio
options:
− - "Standard production test report, unwitnessed"
− - "Witnessed factory acceptance test by Owner's representative"
−default: "Standard production test report, unwitnessed"
+ - "Witnessed by the Owner's representative"
+ - "Certified test report without witnessing"
+default: "Certified test report without witnessing"
```
+### Where witnessing is selected, the manufacturer shall give not less than two weeks' notice of test readiness, shall submit the test procedure for review before the test, and shall not ship the switch until the witness has accepted the results or has waived attendance in writing.
+
## Field Acceptance Tests {toc}
−### Field acceptance testing shall include, at a minimum, the following:
+### Field acceptance tests shall be performed on every switch in accordance with NETA ATS and [[sync/electrical-acceptance-testing]] after installation is complete and before the system is placed in service, and shall include the tests indicated in the datasheet.
−- Visual and mechanical inspection, including verification of conductor torque per the manufacturer's specifications using a calibrated torque tool
−- Insulation resistance testing, phase-to-phase and phase-to-ground, in both source positions
−- Contact resistance measurement on all power-pole connections
−- Mechanical operation verification, including manual operation and lockout in each position
−- Controller setting verification, with each programmable parameter compared to the approved settings record
−- Source-failure simulation, with measurement of TDES, generator-stable time, TDTE, and total time from loss-of-normal to load-on-emergency (≤10 seconds for NFPA 110 Type 10 systems)
−- Source-restored simulation, with measurement of TDRN and TDEC
−- Operation under load on the alternate source for not less than 30 minutes per NFPA 110 §8.4.2
−- Verification of engine start contacts, alarm contacts, communications outputs, and remote annunciator points
−- Closed-transition timing verification (closed-transition switches only) — peak parallel time shall be within the utility's approved limit
−
−### The scope of field testing shall be as indicated in the datasheet.
−
```datasheet
−label: Field Testing Requirements
−type: radio
+label: Field Acceptance Tests
+type: checkbox
options:
− - "NETA acceptance testing plus manufacturer startup and commissioning"
− - "NETA acceptance testing without manufacturer commissioning"
− - "Manufacturer startup and commissioning without independent NETA testing"
−default: "NETA acceptance testing plus manufacturer startup and commissioning"
+ - "Visual and mechanical inspection including anchorage, nameplate, and clearances"
+ - "Bolted connection resistance or torque verification"
+ - "Manual transfer operation in each direction"
+ - "Mechanical interlock verification in each position"
+ - "Insulation resistance, phase-to-phase and phase-to-ground, in each position"
+ - "Contact resistance across each pole in each position"
+ - "Controller settings verification against the reviewed settings record"
+ - "Normal source failure simulation with measurement of the engine-start delay, the source stabilization time, the transfer delay, and the total restoration time"
+ - "Normal source restoration simulation with measurement of the retransfer delay and the unloaded running delay"
+ - "Center-off dwell measurement on a delayed-transition switch"
+ - "Parallel duration measurement on a closed-transition switch"
+ - "Neutral overlap verification on a switch with overlapping neutral contacts"
+ - "Bypass-isolation operating sequence on a switch so furnished"
+ - "Operation of every auxiliary contact, engine-start contact, load-management input and output, and communications point"
+ - "Exerciser operation"
+ - "Operation under load on the alternate source for not less than 30 minutes"
+default:
+ - "Visual and mechanical inspection including anchorage, nameplate, and clearances"
+ - "Bolted connection resistance or torque verification"
+ - "Manual transfer operation in each direction"
+ - "Mechanical interlock verification in each position"
+ - "Insulation resistance, phase-to-phase and phase-to-ground, in each position"
+ - "Contact resistance across each pole in each position"
+ - "Controller settings verification against the reviewed settings record"
+ - "Normal source failure simulation with measurement of the engine-start delay, the source stabilization time, the transfer delay, and the total restoration time"
+ - "Normal source restoration simulation with measurement of the retransfer delay and the unloaded running delay"
+ - "Operation of every auxiliary contact, engine-start contact, load-management input and output, and communications point"
+ - "Exerciser operation"
+ - "Operation under load on the alternate source for not less than 30 minutes"
```
−### Whether NFPA 110 §8 acceptance test documentation is required shall be as indicated in the datasheet.
+### The measured total restoration time shall be within the limit derived for the article the switch serves, and a switch whose measured time exceeds that limit shall not be placed in service until the cause is corrected and the test repeated.
+### Where the switch serves a system classified under NFPA 110, the field acceptance tests shall be performed as part of the installation acceptance test NFPA 110 Chapter 7 requires, and the record shall be signed and delivered with the closeout submittals.
+
+### Whether the manufacturer performs a field startup shall be as indicated in the datasheet.
+
```datasheet
−label: NFPA 110 Acceptance Test Documentation
+label: Manufacturer Field Startup
type: radio
options:
− - "Not applicable (NEC Article 702 optional standby)"
− - "Required per NFPA 110 §8 (emergency/legally required standby)"
+ - "Not required"
+ - "Required, with a startup report"
```
−### Whether NFPA 110 §8 applies follows from the NEC article the system is designed to, so the field carries no default. {note}
+### Where manufacturer field startup is required, the manufacturer's technician shall verify the installation, set the controller to the reviewed settings record, and witness the source failure and restoration simulations, and shall furnish the startup report required in the closeout submittals.
−### Where independent NETA testing is indicated in the datasheet, the Contractor shall engage a qualified independent testing firm to perform field acceptance testing per ANSI/NETA ATS and the additional requirements of NFPA 110 §8 where applicable.
+### The field acceptance tests of every switch shall be scheduled with the generator field tests required under [[sync/generators]] so that they roll up into the integrated system test required under [[sync/emergency-and-standby-power]], and the chain from source failure to load restoration is verified as one system.
−### Where manufacturer startup and commissioning is indicated in the datasheet, the manufacturer shall perform its startup and commissioning procedure and shall furnish the report required in the closeout submittals.
+### A switch that fails a field acceptance test shall not be placed in service, the Contractor shall report the failure to the Engineer of Record within one working day with the measured values, and the cost of the correction and of every repeated test shall be borne by the Contractor.
−### Field acceptance testing shall occur after installation is complete and before the system is placed in service.
−
−### Field acceptance testing shall be coordinated with the generator startup and testing required by [[sync/generators]] so that the complete normal/alternate-source/transfer-switch chain is verified as a system, not as isolated components.
−
−### A failure or anomaly observed at the transfer switch during integrated testing shall be addressed before placing the system in service.
−
# Installation {toc}
−## Coordination and Sequencing {toc}
+## Placement and Working Space {toc}
−### The Contractor shall coordinate transfer switch installation with the upstream service or distribution equipment, the alternate source, the loads served, and the building automation interface.
+### The switch shall be installed at the location and in the orientation indicated on [[drawing: the electrical plans]], and its room shall satisfy [[sync/electrical-rooms]].
−### Conduit and conductor routing for the engine-start signal, generator power feeder, and communications cabling shall be planned to avoid conflicts and to maintain separation requirements where the system is an Article 700 emergency system.
+### Working space in front of the switch and at every door shall comply with NEC 110.26 for the system voltage, and the door swing shall not reduce that space.
−## Concrete Housekeeping Pad {toc}
+### Working space shall not be used for storage and shall be kept clear.
−### Floor-standing transfer switches shall be mounted on a reinforced concrete housekeeping pad extending a minimum of 3 in. beyond the base of the equipment on all sides.
+### A floor-standing switch shall be set on a concrete housekeeping pad constructed under [[sync/concrete-pads]], extending not less than 3 in. beyond the enclosure on every side and not less than 4 in. above the finished floor indoors or 6 in. above finished grade outdoors.
−### The pad shall be a minimum of 4 in. above finished floor for indoor installations and 6 in. above finished grade for outdoor installations.
+### The switch shall be anchored at the manufacturer's anchor points with anchors sized for the seismic loads applicable to the installation, in accordance with the seismic anchorage calculation submitted under this standard.
−### Anchor bolt locations shall be coordinated with the manufacturer's shop drawings prior to concrete placement.
+## Conductor Termination {toc}
−## Working Clearance {toc}
+### Source and load conductors shall be terminated on the lugs furnished with the switch, and where field-furnished lugs are used they shall be listed for the conductor material and size.
−### Working space at the transfer switch shall comply with NFPA 70 Article 110.26 based on the nominal voltage and the energized parts likely to require examination, adjustment, servicing, or maintenance while energized.
+### Every power termination shall be torqued to the manufacturer's published value with a calibrated torque tool, and the value shall be recorded on the field test report.
−### Working space shall not be used for storage and shall not be obstructed.
+### Aluminum conductors shall be terminated on lugs listed for aluminum, with the conductor prepared and the joint compound applied as the lug listing requires.
−## Conductor Termination {toc}
+### Conductor selection and installation shall comply with [[sync/conductors-and-cables]].
−### Source and load feeders shall be terminated on the lugs provided by the manufacturer.
+## Grounding and Bonding {toc}
−### Where field-furnished lugs are used, they shall be listed for the conductor material and size, and they shall be torqued to the manufacturer's specified torque using a calibrated torque tool.
+### The enclosure shall be bonded to the equipment grounding conductors of both sources and of the load in accordance with NEC Article 250 and [[sync/grounding-and-bonding]].
−### Aluminum conductors shall be terminated with listed Al/Cu lugs and anti-oxidant compound where required by the lug manufacturer.
+### The system bonding jumper and grounding electrode connection of the alternate source shall be installed, or omitted, in accordance with the neutral treatment selected under this standard, and the Contractor shall record the as-installed condition on the as-built one-line diagram.
−### Conductor sizing and selection shall follow [[sync/conductors-and-cables]].
+### Where the switch is service equipment, the grounded conductor and the grounding electrode connections shall comply with NEC 250.24 and [[sync/electrical-service-entrance]].
−## Grounding and Bonding {toc}
+## Wiring Separation {toc}
−### Grounding and bonding shall be in accordance with [[sync/grounding-and-bonding]] and NEC Article 250.
+### Where the switch serves an Article 700 emergency system, the feeder from the alternate source to the switch and the feeder from the switch to the emergency loads shall be kept entirely independent of all other wiring in accordance with NEC 700.10(B), and the switch enclosure shall contain no wiring other than the emergency system wiring and the wiring NEC 700.10(B) permits within transfer equipment.
−### For 4-pole (switched-neutral) transfer switches, the generator becomes a separately derived system per NEC 250.30 and shall have a system bonding jumper installed at the generator (or at the first system disconnecting means on the generator side), and a grounding electrode conductor connected at the same point.
+### Where the switch serves an Article 701 legally required standby system, the wiring may share raceways and enclosures with other wiring where NEC 701.10 permits it.
−### The system bonding jumper shall not exist at more than one point.
+### The Contractor shall plan the routing of the source feeders, the engine-start wiring, and the communications cabling before rough-in so that the separation the article requires is achieved without rerouting, in accordance with [[sync/raceways-and-conduit]].
−### For 3-pole (solid-neutral) transfer switches, the generator is not a separately derived system and shall not have a neutral-to-ground bond at the generator.
+## Energization {toc}
−## Article 700 Routing Separation {toc}
+### Before energization, the Contractor shall remove every shipping brace, blocking, and packaging material from the enclosure, and shall record their removal on the field test report.
−### For emergency system transfer switches per NEC Article 700, the wiring of the emergency system shall be kept entirely independent of all other wiring and equipment, in accordance with NEC 700.10(B).
+### Before energization, the Contractor shall confirm the neutral treatment of the switch against the neutral bonding installed at the alternate source, and shall not energize a switch whose neutral treatment and source bonding do not agree.
−### The Contractor shall confirm that the feeder from the alternate source to the transfer switch, and the feeder from the transfer switch to the emergency loads, are routed in dedicated raceways and enclosures as required by the article.
+### Before energization, the Contractor shall set the controller to the reviewed settings record and shall confirm the settings against the record.
+### The switch shall be energized from the normal source first with the alternate source disabled, and the alternate source shall be enabled only after the switch position, the phase rotation on both sources, and the controller indications have been verified.
+
# Delivery, Storage, and Handling {toc}
−## Transfer switches shall be delivered in the manufacturer's original protective packaging with all listing marks intact.
+## The switch shall be delivered in the manufacturer's packaging with the listing marks and the nameplate intact, and shall be inspected for shipping damage at receipt.
−## Equipment shall be stored indoors in a clean, dry, climate-controlled location.
+## The switch shall be stored indoors in a clean, dry space where the temperature is held above the dew point, and where indoor storage is not available it shall be stored in weatherproof packaging with the enclosure protected from condensation, precipitation, dust, and physical damage.
−## Where indoor storage is not available, the manufacturer shall provide weatherproof packaging and the Contractor shall protect the equipment from condensation, precipitation, dust, and physical damage.
+## Where the switch will stand more than 30 days in an unconditioned space before energization, its space heater, where furnished, shall be energized from a temporary source, or the enclosure shall otherwise be protected from condensation.
−## Equipment stored for more than 30 days in an unconditioned environment shall have its enclosure heater energized, where furnished, or shall be otherwise protected from condensation.
+## The switch shall be lifted by the lifting provisions the manufacturer identifies and shall not be lifted by the enclosure door, the operating handles, or the terminal lugs.
−## Shipping braces and protective covers shall be removed only at final installation.
+## A switch damaged in transit, in storage, or in handling shall be repaired or replaced as the manufacturer directs and as the Engineer of Record accepts in writing.
# Warranty {toc}
−## The warranty period shall be as indicated in the datasheet.
+## The manufacturer shall warrant each transfer switch against defects in materials and workmanship for the period indicated in the datasheet, measured from the date of substantial completion.
```datasheet
−label: Warranty Period
−type: select
+label: Manufacturer's Warranty Period
+type: range
+unit: years
options:
− - "1 year from substantial completion"
− - "2 years from substantial completion"
− - "5 years from substantial completion"
−default: "2 years from substantial completion"
+ min: 1
+ max: 5
+ setpoints: [1, 2, 3, 5]
+default: 1
```
−## Extended service coverage shall be furnished as indicated in the datasheet.
+## Where the contract documents state a longer warranty period than the datasheet, the longer period shall govern.
+## The Contractor shall warrant the installation, including every termination, the anchorage, the grounding, and the field-installed accessories, for the project warranty period.
+
+## A repair or replacement performed under this warranty shall itself be warranted for a full new term equal to the original period from the date the repair is completed, or for the remainder of the original period, whichever ends later.
+
+## The emergency field service response time committed for the warranty period shall be as indicated in the datasheet.
+
```datasheet
−label: Extended Service Coverage
−type: checkbox
+label: Emergency Field Service Response Time
+type: range
+unit: hours
options:
− - "Annual preventive maintenance visit"
− - "Controller firmware updates included"
− - "24/7 emergency response with 4-hour commitment"
− - "Parts inventory commitment for the warranty period"
−default:
− - "Annual preventive maintenance visit"
+ min: 4
+ max: 72
+ setpoints: [4, 8, 24, 48, 72]
```
−## Warranty shall cover defects in materials and workmanship under normal use and service conditions.
+## Where the switch serves a system classified as NFPA 110 Level 1, the response time shall be coordinated with the facility's continuity-of-operations plan and with the response commitment made under [[sync/generators]].
−## The manufacturer shall maintain a service organization capable of providing emergency replacement parts and field service within 24 hours during the warranty period.
+## The extended service provisions furnished shall be as indicated in the datasheet.
−## Where the transfer switch serves an emergency or legally required standby system, the response time commitment shall be coordinated with the facility's continuity-of-operations plan.
+```datasheet
+label: Extended Service Provisions
+type: checkbox
+options:
+ - "Annual preventive maintenance visit for the warranty period"
+ - "Controller firmware updates for the warranty period"
+ - "Parts stocking commitment at the nearest service center"
+ - "Extended warranty beyond the period stated"
+```
# Spare Parts {toc}
−## The manufacturer shall provide the spare parts indicated in the datasheet at substantial completion.
+## The Contractor shall deliver the spare parts indicated in the datasheet to the Owner before the switch is accepted, and shall obtain a signed receipt for them.
```datasheet
−label: Spare Parts Furnished
+label: Spare Parts to Be Furnished
type: checkbox
options:
− - "One set of replacement control fuses"
− - "One set of replacement indicating lights / LEDs"
− - "One set of auxiliary contact assemblies"
− - "One spare main contact assembly (frames ≥800 A)"
− - "Manual operation handle / tool"
− - "Complete set of keys for all locks"
+ - "One set of control fuses for each switch"
+ - "One set of indicating lamps or indicators for each controller type"
+ - "One auxiliary contact assembly for each switch type"
+ - "One main contact set for each frame 800 A and larger"
+ - "One manual operating handle for each switch type"
+ - "One controller of each type furnished"
+ - "Keys for every lock furnished"
default:
− - "One set of replacement control fuses"
− - "One set of replacement indicating lights / LEDs"
− - "One set of auxiliary contact assemblies"
− - "Manual operation handle / tool"
− - "Complete set of keys for all locks"
+ - "One set of control fuses for each switch"
+ - "One manual operating handle for each switch type"
+ - "Keys for every lock furnished"
```
−## Spare parts shall be of the same type, rating, and configuration as the installed components and shall be fully interchangeable.
+## Spare parts shall be of the same manufacturer and rating as the installed items, shall be delivered in their original packaging, and shall be labeled with the equipment designation of the switch they serve.
−## Spare parts shall be stored in a clearly labeled cabinet or container in the electrical room or generator room, accessible to maintenance personnel without specialized tools.
+## The Owner's operating personnel shall be trained on the switches for the period indicated in the datasheet, covering normal and manual operation, the bypass-isolation sequence where furnished, the controller interface, the settings record, the exerciser, and the routine inspection and testing NFPA 110 Chapter 8 requires where it applies.
+
+```datasheet
+label: Operator Training Period
+type: range
+unit: hours
+options:
+ min: 0
+ max: 16
+ setpoints: [0, 2, 4, 8, 16]
+```