1 Scope

NOTE 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). (1.1)

1.2 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.

1.3 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.

1.4 The Contractor shall coordinate transfer switch ratings and configuration with the upstream service equipment (see Low Voltage SwitchgearLow Voltage SwitchgearResolves to the current edition.sync/low-voltage-switchgear, Low Voltage SwitchboardsLow Voltage SwitchboardsResolves to the current edition.sync/low-voltage-switchboards, and PanelboardsPanelboardsResolves to the current edition.sync/panelboards), with the alternate source (see GeneratorsEngine GeneratorsResolves to the current edition.sync/generators), with the feeders and branch conductors on both sides of the switch (see Conductors And CablesConductors and CablesResolves to the current edition.sync/conductors-and-cables), and with the grounding and bonding of any separately derived system created by the transfer switch's pole configuration (see Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current edition.sync/grounding-and-bonding).

1.5 Equipment identification and warning labels shall follow Equipment LabelingElectrical Equipment LabelingResolves to the current edition.sync/equipment-labeling.

1.6 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.

1.7 Where the project requires paralleling switchgear, static transfer switches, or manual transfer switches, they shall be specified separately.

2 Referenced Standards

2.1 Equipment and installation shall comply with the latest adopted edition of each of the following standards.

2.2 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.

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)
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
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

3 Submittals

3.1 Action Submittals

3.1.1 Contractor shall submit the following for review prior to fabrication.

3.1.2 Installation shall not proceed until the corresponding submittals have been reviewed and returned.

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

Action Submittals Requiredcheckbox

☑ 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

3.2 Closeout Submittals

3.2.1 Contractor shall provide the following at substantial completion before the 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

Required Closeout Submittalscheckbox

☑ 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

☑ Warranty documentation

☑ Spare parts inventory with reorder information

4 Quality Assurance

4.1 Manufacturer Qualifications

4.1.1 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.

4.1.2 The manufacturer shall maintain a North American service organization capable of dispatching a factory-trained technician on-site within 24 hours of notification.

4.2 Listing and Labeling

4.2.1 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.

4.2.2 UL 1008 listing of components individually is not acceptable; the assembly as furnished shall bear the listing mark.

4.2.3 Transfer switches serving emergency systems per NEC Article 700 shall be UL 1008 listed.

NOTE UL 1008 listing of emergency-system transfer switches is a code requirement, not a project preference. (4.2.4)

4.2.5 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.

4.3 Source Limitations

4.3.1 The transfer switch, its controller, and all factory-installed accessories shall be furnished by a single manufacturer responsible for the complete assembly.

4.3.2 Combining a power switching device from one manufacturer with a third-party controller is not acceptable for global applications under this standard.

4.4 Testing Personnel Qualifications

4.4.1 Field acceptance testing shall be performed by a firm regularly engaged in testing low-voltage power equipment, employing technicians certified by NETA or equivalent.

4.4.2 Testing personnel shall have a minimum of three years of experience testing transfer switch equipment and shall be familiar with the controller furnished.

5 Environmental and Service Conditions

5.1 The transfer switch shall be suitable for continuous operation under the ambient conditions of the installed location.

5.2 Where conditions exceed the manufacturer's standard ratings, the Contractor shall notify the manufacturer and apply derating or alternative construction as required.

5.3 Ambient and Altitude

5.3.1 The design ambient temperature range and the installation altitude shall be as indicated in the datasheet.

Ambient Temperature (Operating)select

0 to 40°C (standard)

-20 to 40°C (cold-climate indoor)

-30 to 50°C (extended outdoor)

Installation Altitudeselect

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

5.4 Outdoor and Unconditioned Installations

5.4.1 Whether an enclosure heater is furnished shall be as indicated in the datasheet.

Enclosure Heaterradio

○ Not required (climate-controlled indoor space)

○ Provided, thermostat-controlled

5.4.2 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.

5.4.3 Outdoor and unconditioned installations should include a thermostatically controlled enclosure heater to prevent condensation on the power conductors, controller, and contact surfaces.

5.5 Seismic Requirements

5.5.1 The seismic certification basis shall be as indicated in the datasheet.

Seismic Certificationselect

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)

Per drawings — structural drawings (deferred by default)

NOTE The Seismic Design Category and Importance Factor are established by the project's structural design; the electrical scope adopts them rather than setting them. (5.5.2)

5.5.3 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.

5.5.4 Transfer switches serving emergency systems, life-safety branches, or essential facilities frequently carry an importance factor of 1.5 and shall be certified accordingly.

6 Ratings

6.1 Amperage Rating

6.1.1 The continuous current rating shall be as indicated in the datasheet.

Continuous Current Ratingrange

A

1001502002604006008001000120016002000260030004000

Per drawings — one-line diagram (deferred by default)

6.1.2 The transfer switch shall be rated for the continuous load current it serves.

6.1.3 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.

6.1.4 The amperage rating shall be selected to match the upstream feeder ampacity and the downstream load with appropriate margin for future growth.

6.2 Voltage, Phases, and Frequency

6.2.1 The nominal system voltage and configuration shall be as indicated in the datasheet.

System Voltageselect

120/240V 1Φ 3-wire

120/208V 3Φ 4-wire

277/480V 3Φ 4-wire

480V 3Φ 3-wire

347/600V 3Φ 4-wire

Per drawings — one-line diagram (deferred by default)

NOTE The number of phases and the number of wires are fixed by the system voltage selected, so they are not offered as separate selections. (6.2.2)

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. (6.2.3)

6.2.4 The system frequency shall be as indicated in the datasheet.

System Frequencyradio

● 60 Hz

○ 50 Hz

NOTE 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. (6.2.5)

6.3 Withstand and Closing Rating (WCR) / Short-Circuit Current Rating (SCCR)

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. (6.3.1)

6.3.2 The basis on which the Withstand and Closing Rating is established shall be as indicated in the datasheet.

Withstand and Closing Rating Basisselect

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)

NOTE The rating basis follows from the overcurrent device actually installed upstream, which is a project coordination outcome, so the field carries no default. (6.3.3)

6.3.4 The available fault current at the transfer switch terminals shall be as indicated in the datasheet.

Available Fault Current at ATS Terminalsrange

kA

102235426585100200

Per drawings — short-circuit study (deferred by default)

6.3.5 The Withstand and Closing Rating of the transfer switch shall be as indicated in the datasheet.

Withstand and Closing Rating (WCR)range

kA

2235426585100200

Per drawings — short-circuit study (deferred by default)

NOTE 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. (6.3.6)

6.3.7 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 Short Circuit StudyShort-Circuit StudyResolves to the current edition.sync/short-circuit-study).

6.3.8 The Contractor shall not select a WCR based on the upstream breaker rating alone.

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. (6.3.9)

6.3.10 Where the upstream overcurrent device is changed, the WCR shall be re-verified against the latest UL 1008 listing data.

6.4 Service Entrance Rating

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. (6.4.1)

6.4.2 Whether the transfer switch is service entrance rated shall be as indicated in the datasheet.

Service Entrance Ratedradio

○ Not service entrance rated

○ Service entrance rated with integral main overcurrent device

Per drawings — one-line diagram (deferred by default)

NOTE Service entrance construction simplifies the equipment layout but ties the transfer switch's WCR to the integral overcurrent device. (6.4.3)

6.4.4 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.

7 The transfer switch shall consist of a mechanically interlocked, double-throw power switching mechanism, a microprocessor-based controller, and an enclosure.

8 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.

9 Power Switching Mechanism

9.1 The power switching mechanism type shall be as indicated in the datasheet.

Switching Mechanism Typeradio

● Contactor-based (electrically operated, mechanically held)

○ Power-frame breaker pair, factory-integrated and interlocked

○ Molded-case switch pair, factory-integrated and interlocked

9.2 The power switching mechanism shall be a single, integrated double-throw device — not two independent breakers tied together by an external interlock.

9.3 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).

9.4 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.

NOTE 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. (9.5)

NOTE 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. (9.6)

10 Manual Operation

10.1 The transfer switch shall include a means for manual operation under no-load conditions to verify mechanism integrity and to permit safe maintenance.

10.2 Manual operation shall be possible only when both sources are de-energized or as otherwise specifically permitted by the listing.

10.3 The manual operation handle or tool shall be stored with the equipment.

11 Auxiliary Contacts

11.1 The auxiliary contacts furnished shall be as indicated in the datasheet.

Auxiliary Contactscheckbox

☑ 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

11.2 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.

11.3 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.

12 Transfer Type

12.1 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.

12.2 Transfer Type Selection

12.2.1 The transfer type shall be as indicated in the datasheet.

Transfer Typeradio

● 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)

12.3 Open Transition

NOTE Open-transition transfer breaks the connection to one source before making the connection to the other. (12.3.1)

NOTE 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. (12.3.2)

NOTE 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. (12.3.3)

12.4 Delayed Transition

NOTE 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. (12.4.1)

12.4.2 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.

NOTE The neutral time is typically programmable from 0 to 60 seconds. (12.4.3)

12.5 Closed Transition

NOTE Closed-transition transfer briefly parallels the two sources (typically for less than 100 ms) so that the load is never de-energized during retransfer. (12.5.1)

12.5.2 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.

12.5.3 Closed transition shall not be assumed without confirmed utility approval.

12.5.4 The Contractor shall obtain written interconnection approval and shall coordinate any required protective relaying, anti-islanding protection, and metering with the utility before procurement.

12.5.5 The closed-transition window shall be set so that the parallel interval is consistent with the utility's approval — typically 100 ms or less.

12.5.6 If the alternate source cannot be synchronized within the controller's permitted window, the controller shall fall back to open or delayed transition automatically.

12.6 Soft-Loading (Closed Transition with Ramped Transfer)

NOTE 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. (12.6.1)

13 Pole Configuration

13.1 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.

13.2 Pole Configuration Selection

13.2.1 The pole configuration shall be as indicated in the datasheet.

Pole Configurationradio

○ 3-pole (solid neutral, neutral not switched)

● 4-pole (switched neutral, fully separated)

○ 3-pole with overlapping neutral (where listed)

13.3 3-Pole (Solid Neutral)

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. (13.3.1)

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. (13.3.2)

13.3.3 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.

13.4 4-Pole (Switched Neutral)

NOTE A 4-pole transfer switch switches the neutral together with the three phase conductors. (13.4.1)

13.4.2 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.

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. (13.4.3)

13.4.4 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.

NOTE When in doubt, 4-pole is the safer default. (13.4.5)

13.4.6 The Contractor shall coordinate the resulting system bonding jumper and grounding electrode connection at the generator with Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current edition.sync/grounding-and-bonding and GeneratorsEngine GeneratorsResolves to the current edition.sync/generators.

13.5 Overlapping Neutral

NOTE 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. (13.5.1)

NOTE An open neutral on a 4-pole transfer of an unbalanced load can cause line-to-neutral voltage excursions on the load. (13.5.2)

13.5.3 Overlapping neutral construction prevents open-neutral voltage excursions and shall be considered for 4-pole switches feeding heavily unbalanced single-phase loads.

14 Bypass-Isolation

14.1 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.

14.2 Bypass-Isolation Selection

14.2.1 Whether bypass-isolation construction is furnished shall be as indicated in the datasheet.

Bypass-Isolationradio

● Not required (standard automatic transfer switch)

○ Bypass-isolation construction (no-load interruption during maintenance)

14.3 Bypass-Isolation Application

14.3.1 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.

NOTE 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. (14.3.2)

14.3.3 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.

14.3.4 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.

15 Controller

15.1 The transfer switch controller shall be microprocessor-based, with a non-volatile memory retaining all settings and event logs across power outages.

15.2 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.

15.3 Controller Display

15.3.1 The controller display shall be as indicated in the datasheet.

Controller Displayselect

Alphanumeric LCD with status LEDs

Graphical LCD with menu navigation

Color touchscreen

Manufacturer's standard (by default)

NOTE 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. (15.3.2)

15.4 Source Sensing

15.4.1 The source sensing functions provided by the controller shall be as indicated in the datasheet.

Source Sensingcheckbox

☑ 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

15.4.2 The controller shall sense voltage on all phases of both the normal and alternate sources and shall sense frequency on the alternate source.

15.4.3 Pickup and dropout setpoints for voltage and frequency shall be independently programmable.

15.4.4 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.

15.4.5 Voltage sensing shall include both pickup and dropout setpoints (with hysteresis) to prevent nuisance transfers from short transients.

15.4.6 Frequency sensing shall be applied to the alternate source to confirm the generator has reached operating frequency before transfer.

15.5 In-Phase Monitor

15.5.1 Whether an in-phase monitor is provided shall be as indicated in the datasheet.

In-Phase Monitorradio

○ Not provided

○ Provided, programmable phase window

15.5.2 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.

NOTE 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). (15.5.3)

15.6 Exerciser Clock

15.6.1 The exerciser schedule shall be as indicated in the datasheet.

Exerciser Scheduleselect

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

15.6.2 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.

15.6.3 NFPA 110 Level 1 systems require a monthly exercise of at least 30 minutes under load or per the manufacturer's recommended test cycle.

15.6.4 NFPA 110 Level 2 systems and NEC Article 700/701 systems have similar but not identical exercise requirements that shall govern.

15.7 Load Shed and Priority

15.7.1 The load-shed and source-priority provisions shall be as indicated in the datasheet.

Load Shed / Source Priorityradio

● Not required (generator sized for full load)

○ Programmable load-shed outputs

○ Source priority coordination across multiple ATS

15.7.2 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.

15.7.4 The Contractor shall coordinate load-shed strategy with GeneratorsEngine GeneratorsResolves to the current edition.sync/generators and the load calculations.

16 Time Delays

16.1 The transfer switch controller shall provide independently programmable time delays for each transfer event.

16.2 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.

16.3 Time-Delay Engine Start (TDES)

16.3.1 The TDES setting shall be as indicated in the datasheet.

Time-Delay Engine Start (TDES)range

s

1351030

NOTE TDES is the time the controller waits after detecting a loss of normal source before signaling the generator to start. (16.3.2)

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. (16.3.3)

16.3.4 For Type 10 systems, total time from loss-of-normal to load-on-emergency shall not exceed 10 seconds.

16.4 Time-Delay Transfer to Emergency (TDTE)

16.4.1 The TDTE setting shall be as indicated in the datasheet.

Time-Delay Transfer to Emergency (TDTE)range

s

1351060

NOTE TDTE is the time the controller waits, after the alternate source is stable, before transferring the load. (16.4.2)

16.4.3 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.

16.5 Time-Delay Retransfer to Normal (TDRN)

16.5.1 The TDRN setting shall be as indicated in the datasheet.

Time-Delay Retransfer to Normal (TDRN)range

min

15101530

NOTE TDRN is the time the controller waits, after the normal source is restored and stable, before retransferring the load. (16.5.2)

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. (16.5.3)

16.6 Time-Delay Engine Cool-Down (TDEC)

16.6.1 The TDEC setting shall be as indicated in the datasheet.

Time-Delay Engine Cool-Down (TDEC)range

min

5101530

Manufacturer's standard (by default)

NOTE TDEC is the time the generator runs unloaded after the load is retransferred to normal, to allow controlled cool-down of the engine. (16.6.2)

16.6.3 The required TDEC value is set by the generator manufacturer and shall be coordinated with GeneratorsEngine GeneratorsResolves to the current edition.sync/generators.

NOTE Skipping cool-down shortens engine life. (16.6.4)

16.7 Time-Delay Neutral (TDN)

16.7.1 The TDN setting shall be as indicated in the datasheet.

Time-Delay Neutral (TDN)range

s

1351060

NOTE 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. (16.7.2)

16.7.3 TDN shall be set based on the motor decay characteristics of the load; 1 to 5 seconds is typical for general-purpose motors.

17 Engine Start Contacts

17.1 The transfer switch shall provide dry, isolated contacts to start the engine-generator.

17.2 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.

17.3 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.

17.4 Engine Start Wiring

Engine Start Wiringradio

● Two-wire start (single contact closure)

○ Three-wire start with separate run signal

17.4.1 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.

17.4.2 The Contractor shall coordinate raceway and conductor types with Conductors And CablesConductors and CablesResolves to the current edition.sync/conductors-and-cables.

18 Communications

18.1 The transfer switch controller shall provide communications appropriate to the project's monitoring and building management integration requirements.

18.2 Communications Interface

18.2.1 The communications interfaces provided at the transfer switch shall be as indicated in the datasheet.

Communications Interfacecheckbox

☐ Dry contacts, no protocol

☐ Modbus RTU (RS-485)

☐ Modbus TCP/IP (Ethernet)

☐ BACnet IP

☐ SNMP

☐ Manufacturer's proprietary protocol over Ethernet

NOTE The protocol follows from the building automation or monitoring platform the project actually uses, so the field carries no default. (18.2.2)

18.2.3 Whether a remote annunciator is provided shall be as indicated in the datasheet.

Remote Annunciator (NFPA 110 Level 1)radio

○ Not required

○ Provided per NFPA 110 §5.6.5

NOTE 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. (18.2.4)

18.2.5 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.

18.2.6 The Contractor shall coordinate with Building Automation SystemBuilding Automation SystemResolves to the current edition.sync/building-automation-system for the points list, addressing, and network connectivity.

18.2.7 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.

19 Enclosure

19.1 The transfer switch enclosure shall match the environmental conditions of the installed location and shall comply with NEMA 250 for the rating selected.

19.2 Enclosure Rating

19.2.1 The enclosure rating shall be as indicated in the datasheet.

Enclosure Ratingselect

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

NOTE NEMA 1 is appropriate for typical indoor electrical rooms with clean, dry, climate-controlled conditions. (19.2.2)

NOTE NEMA 3R is appropriate for outdoor installation in areas not subject to direct wash-down. (19.2.3)

19.2.4 NEMA 4X shall be specified for coastal, chemical, food-processing, or wash-down environments where corrosion resistance is required.

NOTE NEMA 12 is appropriate for industrial spaces with significant airborne dust. (19.2.5)

19.3 Doors, Access, and Conduit Entry

19.3.1 The mounting arrangement shall be as indicated in the datasheet.

Mountingradio

○ Wall mounted

○ Floor standing on concrete housekeeping pad

19.3.2 Wall mounting shall be limited to frames within the manufacturer's published wall-mount rating; all other frames shall be floor standing.

19.3.3 The enclosure shall include hinged front access doors with provisions for padlocking in the closed position.

19.3.4 Doors shall provide access to the controller display, the manual operation handle, and the maintenance terminals without exposing energized power conductors.

19.3.5 Provisions for conduit entry shall accommodate the source and load feeders, control wiring to the generator, and communications cabling.

19.3.6 Conduit entry locations shall be as indicated on the equipment shop drawings.

20 Identification and Labeling

20.1 Identification of the transfer switch shall follow Equipment LabelingElectrical Equipment LabelingResolves to the current edition.sync/equipment-labeling conventions and shall additionally include the items indicated in the datasheet.

Required Identificationcheckbox

☑ 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)

20.2 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.

20.3 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.

20.4 Labels shall be permanent, weather-resistant where exposed, and legible from the front of the equipment without obstruction.

21 Testing

21.1 Factory Tests

21.1.1 The manufacturer shall perform the following production tests on each transfer switch before shipment, with results recorded on a certified test report:

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

21.1.2 Factory acceptance test witnessing shall be as indicated in the datasheet.

Factory Acceptance Testradio

● Standard production test report, unwitnessed

○ Witnessed factory acceptance test by Owner's representative

21.2 Field Acceptance Tests

21.2.1 Field acceptance testing shall include, at a minimum, the following:

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

21.2.2 The scope of field testing shall be as indicated in the datasheet.

Field Testing Requirementsradio

● NETA acceptance testing plus manufacturer startup and commissioning

○ NETA acceptance testing without manufacturer commissioning

○ Manufacturer startup and commissioning without independent NETA testing

21.2.3 Whether NFPA 110 §8 acceptance test documentation is required shall be as indicated in the datasheet.

NFPA 110 Acceptance Test Documentationradio

○ Not applicable (NEC Article 702 optional standby)

○ Required per NFPA 110 §8 (emergency/legally required standby)

NOTE Whether NFPA 110 §8 applies follows from the NEC article the system is designed to, so the field carries no default. (21.2.4)

21.2.5 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.

21.2.6 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.

21.2.7 Field acceptance testing shall occur after installation is complete and before the system is placed in service.

21.2.8 Field acceptance testing shall be coordinated with the generator startup and testing required by GeneratorsEngine GeneratorsResolves to the current edition.sync/generators so that the complete normal/alternate-source/transfer-switch chain is verified as a system, not as isolated components.

21.2.9 A failure or anomaly observed at the transfer switch during integrated testing shall be addressed before placing the system in service.

22 Installation

22.1 Coordination and Sequencing

22.1.1 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.

22.1.2 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.

22.2 Concrete Housekeeping Pad

22.2.1 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.

22.2.2 The pad shall be a minimum of 4 in. above finished floor for indoor installations and 6 in. above finished grade for outdoor installations.

22.2.3 Anchor bolt locations shall be coordinated with the manufacturer's shop drawings prior to concrete placement.

22.3 Working Clearance

22.3.1 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.

22.3.2 Working space shall not be used for storage and shall not be obstructed.

22.4 Conductor Termination

22.4.1 Source and load feeders shall be terminated on the lugs provided by the manufacturer.

22.4.2 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.

22.4.3 Aluminum conductors shall be terminated with listed Al/Cu lugs and anti-oxidant compound where required by the lug manufacturer.

22.4.4 Conductor sizing and selection shall follow Conductors And CablesConductors and CablesResolves to the current edition.sync/conductors-and-cables.

22.5 Grounding and Bonding

22.5.1 Grounding and bonding shall be in accordance with Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current edition.sync/grounding-and-bonding and NEC Article 250.

22.5.2 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.

22.5.3 The system bonding jumper shall not exist at more than one point.

22.5.4 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.

22.6 Article 700 Routing Separation

22.6.1 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).

22.6.2 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.

23 Delivery, Storage, and Handling

23.1 Transfer switches shall be delivered in the manufacturer's original protective packaging with all listing marks intact.

23.2 Equipment shall be stored indoors in a clean, dry, climate-controlled location.

23.3 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.

23.4 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.

23.5 Shipping braces and protective covers shall be removed only at final installation.

24 Warranty

24.1 The warranty period shall be as indicated in the datasheet.

Warranty Periodselect

1 year from substantial completion

2 years from substantial completion

5 years from substantial completion

24.2 Extended service coverage shall be furnished as indicated in the datasheet.

Extended Service Coveragecheckbox

☑ Annual preventive maintenance visit

☐ Controller firmware updates included

☐ 24/7 emergency response with 4-hour commitment

☐ Parts inventory commitment for the warranty period

24.3 Warranty shall cover defects in materials and workmanship under normal use and service conditions.

24.4 The manufacturer shall maintain a service organization capable of providing emergency replacement parts and field service within 24 hours during the warranty period.

24.5 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.

25 Spare Parts

25.1 The manufacturer shall provide the spare parts indicated in the datasheet at substantial completion.

Spare Parts Furnishedcheckbox

☑ 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

25.2 Spare parts shall be of the same type, rating, and configuration as the installed components and shall be fully interchangeable.

25.3 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.