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SynC · Editorial revision

Automatic Transfer Switches

Revision7
EditedSep 14, 2026
StatusCurrent
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Current revision. This is editorial revision 7, the current text of this standard. Read it on the standard's page.

SynC Standards Team — Specifier (Platform Standards) ✓ OfficialDiscloses employment SynC (SynC Platform Team)
Remake for template neutrality (from-scratch field inventory, five-state defaults, parameters and derived fields, schedule deferrals)

1 Scope

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. (1.1)
NOTE 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. (1.2)
NOTE 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. (1.3)
NOTE The following are governed elsewhere and are outside this standard: (1.4)
  • the classification of loads, the selection of the alternate source, the number and segregation of transfer switches, and the transfer scheme (Emergency And Standby PowerEmergency and Standby Power SystemsResolves to the current adopted revision.sync/emergency-and-standby-power)
  • the engine-generator set, its controller, and its remote annunciator (GeneratorsEngine GeneratorsResolves to the current adopted revision.sync/generators)
  • the branch assignment and topology of a health care essential electrical system (Healthcare Essential Electrical SystemsHealthcare Essential Electrical SystemsResolves to the current adopted revision.sync/healthcare-essential-electrical-systems)
  • the switchgear, switchboards, and panelboards on either side of the switch (Low Voltage SwitchgearLow Voltage SwitchgearResolves to the current adopted revision.sync/low-voltage-switchgear, Low Voltage SwitchboardsLow Voltage SwitchboardsResolves to the current adopted revision.sync/low-voltage-switchboards, PanelboardsPanelboardsResolves to the current adopted revision.sync/panelboards)
  • the feeders on both sides of the switch and their raceways (Conductors And CablesConductors and CablesResolves to the current adopted revision.sync/conductors-and-cables, Raceways And ConduitRaceways and ConduitResolves to the current adopted revision.sync/raceways-and-conduit)
  • the grounding electrode system and the bonding of a separately derived system (Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding)
  • the short-circuit, coordination, and arc-flash studies that establish the ratings and settings the switch is ordered to (Short Circuit StudyShort-Circuit StudyResolves to the current adopted revision.sync/short-circuit-study, Protective Coordination StudyProtective Device Coordination StudyResolves to the current adopted revision.sync/protective-coordination-study, Arc Flash StudyArc-Flash Hazard AnalysisResolves to the current adopted revision.sync/arc-flash-study)
  • the room the switch occupies (Electrical RoomsElectrical RoomsResolves to the current adopted revision.sync/electrical-rooms) and the concrete pad as a structure (Concrete PadsConcrete Equipment PadsResolves to the current adopted revision.sync/concrete-pads)
  • manual and non-automatic transfer switches, medium-voltage transfer schemes, static transfer switches, and paralleling switchgear
1.5 The location of each transfer switch shall be as indicated on the electrical plans.
1.6 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.

2 Referenced Standards

2.1 Equipment, materials, and installation shall comply with the latest adopted edition of each of the following unless a specific edition is cited.
2.2 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 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
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)
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

3 Submittals

3.1 Action Submittals

3.1.1 The Contractor shall submit the following for review before any transfer switch is released for manufacture:
  • 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
Action Submittalscheckbox
☑ 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
3.1.2 A transfer switch shall not be released for manufacture until the action submittals covering it have been reviewed and returned.
NOTE 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. (3.1.3)

3.2 Informational Submittals

3.2.1 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
Informational Submittalscheckbox
☑ Manufacturer's qualification statement
☐ Utility approval of parallel operation
☐ Factory test procedure
☑ Field testing firm qualification and test procedure
☑ Seismic anchorage calculation and detail

3.3 Closeout Submittals

3.3.1 The Contractor shall submit the following before any transfer switch is accepted:
  • 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
Closeout Submittalscheckbox
☑ 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 receipt
NOTE 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. (3.3.2)

4 Quality Assurance

4.1 Manufacturer Qualifications

4.1.1 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.
Minimum Manufacturer Production Experiencerange
years
351020
4.1.2 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.

4.2 UL 1008 Listing

4.2.1 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.
4.2.2 A switch whose components are individually listed but whose assembly is not shall not be furnished.
4.2.3 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).
4.2.4 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 Healthcare Essential Electrical SystemsHealthcare Essential Electrical SystemsResolves to the current adopted revision.sync/healthcare-essential-electrical-systems.
4.2.5 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.

4.3 Field Testing Firm Qualifications

4.3.1 Field acceptance testing shall be performed by an independent testing firm qualified in accordance with Electrical Acceptance TestingElectrical Acceptance TestingResolves to the current adopted revision.sync/electrical-acceptance-testing.
4.3.2 The technician who performs the functional and timing tests shall have documented experience commissioning the controller family furnished.

5 Environmental and Service Conditions

5.1 Ambient Temperature

5.1.1 The transfer switch shall carry its ratings continuously at the design ambient temperature of the space it is installed in.
5.1.2 The design ambient temperature for a switch installed indoors shall be as indicated in the datasheet.
Indoor Design Ambient Temperaturerange
°C
25304050
NOTE 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. (5.1.3)
5.1.4 A switch installed outdoors or in a space that follows the outdoor temperature shall be rated for Site Ambient Temperature MaximumSite Ambient Temperature MaximumParameterEach project supplies its own value.site-ambient-temperature-maximum where that temperature exceeds 40°C, and the manufacturer shall state the correction applied.

5.2 Altitude

5.2.1 The transfer switch shall be de-rated for AltitudeAltitudeParameterEach project supplies its own value.altitude in accordance with the manufacturer's published correction factors where the altitude exceeds the rating basis of the listing.
NOTE 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. (5.2.2)

5.3 Condensation Control

5.3.1 The space heater provision for the enclosure shall be as indicated in the datasheet.
Enclosure Space Heaterradio
○ No space heater
○ Space heater with thermostat
○ Space heater with thermostat and humidistat
NOTE 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. (5.3.2)
5.3.3 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.
5.3.4 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.

5.4 Seismic Qualification

5.4.1 The seismic certification required for the transfer switch shall be as indicated in the datasheet.
Seismic Certification Requirementselect
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
Derived — Seismic Design CategorySeismic Design CategoryParameterEach project supplies its own value.seismic-design-category and the component importance factor assigned to the switch under ASCE 7 Chapter 13 (by default)
NOTE 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. (5.4.2)
5.4.3 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.

6 System Classification

NOTE 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. (6.1)
6.2 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.
NEC Article and Branch Servedselect
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
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 (by default)
6.3 A transfer switch serving an Article 700 emergency system shall supply only emergency loads in accordance with NEC 700.5(D).
6.4 The NFPA 110 level of the system the switch serves shall be as indicated in the datasheet.
NFPA 110 Levelselect
Level 1
Level 2
Not classified under NFPA 110
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 (by default)
6.5 The NFPA 110 type of the system the switch serves shall be as indicated in the datasheet.
NFPA 110 Typeselect
Type U
Type 10
Type 60
Type 120
Type M
Not classified under NFPA 110
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 (by default)
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. (6.6)
NOTE 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 Uninterruptible Power Supply SystemsUninterruptible Power Supply SystemsResolves to the current adopted revision.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. (6.7)

7 Ratings

7.1 Continuous Current Rating

7.1.1 The continuous current rating of the switch shall be as indicated in the datasheet.
Continuous Current Ratingrange
A
3040607010012515020022526030040060080010001200160020002500300040005000
Per drawings — the one-line diagram (deferred by default)
7.1.2 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.
7.1.3 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.
NOTE 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. (7.1.4)
7.1.5 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.

7.2 Voltage and Frequency

7.2.1 The system voltage of the switch shall be as indicated in the datasheet.
System Voltageselect
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
Per drawings — the one-line diagram (deferred by default)
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. (7.2.2)
7.2.3 The rated frequency of the switch shall be as indicated in the datasheet.
Rated Frequencyradio
● 60 Hz
○ 50 Hz

7.3 Withstand and Closing Rating

NOTE 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. (7.3.1)
7.3.2 The basis on which the withstand and closing rating of the switch is established shall be as indicated in the datasheet.
Withstand and Closing Rating Basisselect
Specific-breaker rating, with the upstream breaker named in the listing
Any-breaker rating
Current-limiting fuse rating
Integral overcurrent device rating
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. (7.3.3)
7.3.4 The withstand and closing rating of the switch shall be as indicated in the datasheet.
Withstand and Closing Ratingrange
kA
1014182225303542506585100150200
Per drawings — the one-line diagram (deferred by default)
7.3.5 The withstand and closing rating shall equal or exceed the available fault current at the switch terminals from either source as established under Short Circuit StudyShort-Circuit StudyResolves to the current adopted revision.sync/short-circuit-study, with the upstream overcurrent device that the study and Protective Coordination StudyProtective Device Coordination StudyResolves to the current adopted revision.sync/protective-coordination-study fix for that source.
7.3.6 The Contractor shall not select a withstand and closing rating from the interrupting rating of the upstream breaker alone.
7.3.7 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.

7.4 Short-Time Withstand Rating

NOTE 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. (7.4.1)
7.4.2 The short-time withstand duration of the switch shall be as indicated in the datasheet.
Short-Time Withstand Durationrange
cycles
31830
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 (by default)
NOTE 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. (7.4.3)
7.4.4 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.

7.5 Service-Entrance Construction

7.5.1 Whether the switch is furnished as service equipment shall be as indicated in the datasheet.
Service-Entrance Constructionradio
○ Not service equipment
○ Service equipment with integral service disconnect and overcurrent device
Per drawings — the one-line diagram (deferred by default)
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. (7.5.2)
7.5.3 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 Electrical Service EntranceElectrical Service EntranceResolves to the current adopted revision.sync/electrical-service-entrance requires at the service.
7.5.4 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.
7.5.5 The integral overcurrent protection furnished with a switch that is not service equipment shall be as indicated in the datasheet.
Integral Overcurrent Protectionselect
None
On the normal source only
On the alternate source only
On both sources
7.5.6 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 the one-line diagram.

8 Power Switching Mechanism

8.1 Mechanism Type

8.1.1 The power switching mechanism type shall be as indicated in the datasheet.
Switching Mechanism Typeradio
● Contactor type, double-throw
○ Molded-case switch or molded-case breaker pair
○ Power circuit breaker pair
NOTE 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. (8.1.2)
8.1.3 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.
8.1.4 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.
8.1.5 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.
8.1.6 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.
8.1.7 Arc chutes or arc barriers shall be furnished on each pole and shall be removable for contact inspection.

8.2 Transition Type

8.2.1 The transition type shall be as indicated in the datasheet.
Transition Typeradio
● Open transition
○ Delayed transition with a programmed center-off dwell
○ Closed transition with a momentary parallel
○ Closed transition with soft loading
NOTE 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. (8.2.2)
NOTE 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. (8.2.3)
NOTE 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. (8.2.4)
NOTE 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. (8.2.5)
NOTE 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. (8.2.6)
8.2.7 Where the datasheet selects a delayed transition, the center-off dwell shall be programmable at the controller and shall be set under this standard.
8.2.8 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.
8.2.9 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.
8.2.10 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.
8.2.11 The maximum duration of the momentary parallel shall be as indicated in the datasheet.
Momentary Parallel Duration Limitrange
ms
20501001502005001000
Derived — the maximum parallel duration the serving utility's written approval of parallel operation permits (by default)
8.2.12 The soft-load ramp duration shall be as indicated in the datasheet.
Soft-Load Ramp Durationrange
s
12510203060
NOTE 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. (8.2.13)
8.2.14 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.

8.3 Bypass-Isolation Construction

8.3.1 Whether bypass-isolation construction is furnished shall be as indicated in the datasheet.
Bypass-Isolation Constructionradio
● Not furnished
○ Furnished
NOTE 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. (8.3.2)
8.3.3 Where the switch serves a health care essential electrical system branch, the bypass-isolation provision shall be as selected under Healthcare Essential Electrical SystemsHealthcare Essential Electrical SystemsResolves to the current adopted revision.sync/healthcare-essential-electrical-systems.
8.3.4 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.
8.3.5 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.
8.3.6 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.
8.3.7 Where bypass-isolation construction is furnished, the automatic mechanism shall be withdrawable or removable for replacement while the bypass carries the load.

8.4 Neutral Treatment

8.4.1 The neutral treatment of the switch shall be as indicated in the datasheet.
Neutral Treatmentradio
○ No neutral pole, three-wire system
○ Solid neutral, not switched
○ Switched neutral
○ Switched neutral with overlapping contacts
NOTE 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 GeneratorsEngine GeneratorsResolves to the current adopted revision.sync/generators and the separately derived system provisions of Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding. (8.4.2)
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. (8.4.3)
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. (8.4.4)
8.4.5 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.
8.4.6 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 Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding, and the system bonding jumper shall exist at one point only.
8.4.7 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.
NOTE 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. (8.4.8)
8.4.9 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.

8.5 Manual Operation

8.5.1 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.
8.5.2 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.
8.5.3 The manual operator or its detachable handle shall be stored inside the enclosure or in a holder fixed to the enclosure exterior.

8.6 Auxiliary Contacts

8.6.1 The auxiliary contacts furnished on the switch shall be as indicated in the datasheet.
Auxiliary Contactscheckbox
☑ 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
8.6.2 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.
8.6.3 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.

9 Controller

9.1 Controller Construction

9.1.1 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.
9.1.2 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.
9.1.3 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.
9.1.4 The controller display shall be as indicated in the datasheet.
Controller Displayselect
Alphanumeric display with status indicators
Graphical display with menu navigation
Color touchscreen
Manufacturer's standard (by default)
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. (9.1.5)
9.1.6 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.

9.2 Source Sensing

9.2.1 The source sensing functions provided by the controller shall be as indicated in the datasheet.
Source Sensing Functionscheckbox
☑ 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
9.2.2 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.
9.2.3 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.
9.2.4 Where the datasheet selects a closed transition or soft loading, the phase-angle sensing function shall be furnished.
9.2.5 The undervoltage dropout set point on the normal source shall be as indicated in the datasheet.
Normal Source Undervoltage Dropout Set Pointrange
% of nominal
707580859095
9.2.6 The undervoltage pickup set point on the normal source shall be as indicated in the datasheet.
Normal Source Undervoltage Pickup Set Pointrange
% of nominal
80859095100
9.2.7 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.
NOTE 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. (9.2.8)

9.3 In-Phase Monitor

9.3.1 Whether an in-phase monitor is furnished shall be as indicated in the datasheet.
In-Phase Monitorradio
○ Not furnished
○ Furnished
NOTE 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. (9.3.2)
9.3.3 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.

9.4 Time Delays

9.4.1 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.
9.4.2 The time delay on engine start shall be as indicated in the datasheet.
Time Delay on Engine Startrange
s
0.51235101530
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. (9.4.3)
9.4.4 The time delay on transfer to the alternate source shall be as indicated in the datasheet.
Time Delay on Transfer to the Alternate Sourcerange
s
1235103060120300
NOTE 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. (9.4.5)
9.4.6 The time delay on retransfer to the normal source shall be as indicated in the datasheet.
Time Delay on Retransfer to the Normal Sourcerange
min
12510153060
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. (9.4.7)
9.4.8 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.
9.4.9 The time delay for unloaded running of the alternate source shall be as indicated in the datasheet.
Time Delay for Unloaded Running of the Alternate Sourcerange
min
125101530
Derived — the unloaded cool-down run time the generator manufacturer publishes for the set furnished under the generator standard (by default)
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. (9.4.10)
9.4.11 The center-off dwell for a delayed transition shall be as indicated in the datasheet.
Delayed Transition Center-Off Dwellrange
s
0.51235103060120
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. (9.4.12)
9.4.13 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.
9.4.14 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.
9.4.15 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.

9.5 Exerciser

9.5.1 The controller shall include an exerciser that starts the alternate source on a programmed schedule, with the schedule retained through loss of both sources.
9.5.2 The exercise interval shall be as indicated in the datasheet.
Exercise Intervalrange
days
714306090
9.5.3 The exercise period shall be as indicated in the datasheet.
Exercise Periodrange
min
510153060120
9.5.4 Whether the load is transferred to the alternate source during the exercise shall be as indicated in the datasheet.
Load Transfer During Exerciseradio
○ Alternate source started and run without transferring the load
○ Load transferred to the alternate source for the exercise period
NOTE 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. (9.5.5)
9.5.6 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.
9.5.7 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.

9.6 Load Management

9.6.1 The load-management provisions furnished shall be as indicated in the datasheet.
Load Management Provisionscheckbox
☐ 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
NOTE 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 Emergency And Standby PowerEmergency and Standby Power SystemsResolves to the current adopted revision.sync/emergency-and-standby-power and configured at each switch. (9.6.2)
9.6.3 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.
9.6.4 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.
9.6.5 The Contractor shall set the load-management provisions of every switch on the project to the sequence established under Emergency And Standby PowerEmergency and Standby Power SystemsResolves to the current adopted revision.sync/emergency-and-standby-power and shall demonstrate that sequence during the integrated system test.

9.7 Engine-Start Contacts

9.7.1 The engine-start wiring arrangement shall be as indicated in the datasheet.
Engine-Start Wiring Arrangementradio
● Two-wire start
○ Three-wire start
NOTE 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. (9.7.2)
9.7.3 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.
9.7.4 The engine-start contact shall be arranged so that loss of control power at the switch calls for the engine to start.
9.7.5 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.

9.8 Communications

9.8.1 The communications interfaces furnished at the switch shall be as indicated in the datasheet.
Communications Interfacescheckbox
☐ Dry contacts only
☐ Modbus RTU serial
☐ Modbus TCP
☐ BACnet MS/TP
☐ BACnet/IP
☐ SNMP
☐ Proprietary protocol over Ethernet
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. (9.8.2)
9.8.3 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 Building Automation SystemBuilding Automation SystemResolves to the current adopted revision.sync/building-automation-system.
9.8.4 Where a remote annunciator is furnished under GeneratorsEngine GeneratorsResolves to the current adopted revision.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.

10 Enclosure

10.1 Enclosure Type

10.1.1 The enclosure type shall be as indicated in the datasheet.
Enclosure Typeselect
NEMA Type 1
NEMA Type 2
NEMA Type 3R
NEMA Type 4
NEMA Type 4X
NEMA Type 12
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. (10.1.2)
10.1.3 The enclosure shall comply with NEMA 250 and UL 50E for the type selected, and the type shall be marked on the enclosure.
NOTE 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. (10.1.4)
10.1.5 A switch installed outdoors shall have an enclosure of Type 3R, Type 4, or Type 4X.
10.1.6 A switch installed where it is subject to hose-directed water or wash-down shall have an enclosure of Type 4 or Type 4X.
10.1.7 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.
10.1.8 A switch installed indoors where airborne dust, lint, or fibers accumulate shall have an enclosure of Type 12, Type 4, or Type 4X.
10.1.9 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.
10.1.10 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.

10.2 Enclosure Material and Access

10.2.1 The enclosure material shall be as indicated in the datasheet.
Enclosure Materialselect
Painted steel
Type 304 stainless steel
Type 316 stainless steel
Non-metallic
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. (10.2.2)
10.2.3 Where the datasheet selects a Type 4X enclosure, the enclosure material shall be one for which the Type 4X rating is listed.
10.2.4 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.
10.2.5 The power terminals shall be furnished with lugs listed for the conductor material, size, and quantity as indicated on the one-line diagram and the feeder schedule.
10.2.6 Conduit entry shall be from the top, the bottom, or the side as indicated on the electrical plans, and the entry area shall be sized for the source and load feeders, the engine-start wiring, and the communications cabling.

10.3 Mounting Arrangement

10.3.1 The mounting arrangement shall be as indicated in the datasheet.
Mounting Arrangementradio
○ Wall mounted
○ Floor standing
Per drawings — the electrical plans (deferred by default)
10.3.2 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.

11 Identification and Labeling

11.1 Field-installed labels shall be provided as indicated in the datasheet and shall comply with Equipment LabelingElectrical Equipment LabelingResolves to the current adopted revision.sync/equipment-labeling.
Transfer Switch Labelingcheckbox
☑ 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
11.2 The available fault current at the switch terminals shall be field-marked with the date of the calculation in accordance with NEC 110.24.
11.3 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).
11.4 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.
11.5 The arc-flash warning label shall carry the values established under Arc Flash StudyArc-Flash Hazard AnalysisResolves to the current adopted revision.sync/arc-flash-study for the switch, and shall be placed so that it is read before the door is opened.
11.6 Labels shall be permanent, resistant to the environment the enclosure type is selected for, and legible from the operating position without removing a cover.

12 Testing

12.1 Factory Production Tests

12.1.1 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 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
12.1.2 Factory test witnessing shall be as indicated in the datasheet.
Factory Test Witnessingradio
○ Witnessed by the Owner's representative
● Certified test report without witnessing
12.1.3 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.

12.2 Field Acceptance Tests

12.2.1 Field acceptance tests shall be performed on every switch in accordance with NETA ATS and Electrical Acceptance TestingElectrical Acceptance TestingResolves to the current adopted revision.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.
Field Acceptance Testscheckbox
☑ 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
12.2.2 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.
12.2.3 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.
12.2.4 Whether the manufacturer performs a field startup shall be as indicated in the datasheet.
Manufacturer Field Startupradio
○ Not required
○ Required, with a startup report
12.2.5 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.
12.2.6 The field acceptance tests of every switch shall be scheduled with the generator field tests required under GeneratorsEngine GeneratorsResolves to the current adopted revision.sync/generators so that they roll up into the integrated system test required under Emergency And Standby PowerEmergency and Standby Power SystemsResolves to the current adopted revision.sync/emergency-and-standby-power, and the chain from source failure to load restoration is verified as one system.
12.2.7 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.

13 Installation

13.1 Placement and Working Space

13.1.1 The switch shall be installed at the location and in the orientation indicated on the electrical plans, and its room shall satisfy Electrical RoomsElectrical RoomsResolves to the current adopted revision.sync/electrical-rooms.
13.1.2 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.
13.1.3 Working space shall not be used for storage and shall be kept clear.
13.1.4 A floor-standing switch shall be set on a concrete housekeeping pad constructed under Concrete PadsConcrete Equipment PadsResolves to the current adopted revision.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.
13.1.5 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.

13.2 Conductor Termination

13.2.1 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.
13.2.2 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.
13.2.3 Aluminum conductors shall be terminated on lugs listed for aluminum, with the conductor prepared and the joint compound applied as the lug listing requires.
13.2.4 Conductor selection and installation shall comply with Conductors And CablesConductors and CablesResolves to the current adopted revision.sync/conductors-and-cables.

13.3 Grounding and Bonding

13.3.1 The enclosure shall be bonded to the equipment grounding conductors of both sources and of the load in accordance with NEC Article 250 and Grounding And BondingGrounding and Bonding for Electrical SystemsResolves to the current adopted revision.sync/grounding-and-bonding.
13.3.2 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.
13.3.3 Where the switch is service equipment, the grounded conductor and the grounding electrode connections shall comply with NEC 250.24 and Electrical Service EntranceElectrical Service EntranceResolves to the current adopted revision.sync/electrical-service-entrance.

13.4 Wiring Separation

13.4.1 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.
13.4.2 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.
13.4.3 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 Raceways And ConduitRaceways and ConduitResolves to the current adopted revision.sync/raceways-and-conduit.

13.5 Energization

13.5.1 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.
13.5.2 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.
13.5.3 Before energization, the Contractor shall set the controller to the reviewed settings record and shall confirm the settings against the record.
13.5.4 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.

14 Delivery, Storage, and Handling

14.1 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.
14.2 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.
14.3 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.
14.4 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.
14.5 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.

15 Warranty

15.1 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.
Manufacturer's Warranty Periodrange
years
1235
15.2 Where the contract documents state a longer warranty period than the datasheet, the longer period shall govern.
15.3 The Contractor shall warrant the installation, including every termination, the anchorage, the grounding, and the field-installed accessories, for the project warranty period.
15.4 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.
15.5 The emergency field service response time committed for the warranty period shall be as indicated in the datasheet.
Emergency Field Service Response Timerange
hours
48244872
15.6 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 GeneratorsEngine GeneratorsResolves to the current adopted revision.sync/generators.
15.7 The extended service provisions furnished shall be as indicated in the datasheet.
Extended Service Provisionscheckbox
☐ 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

16 Spare Parts

16.1 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.
Spare Parts to Be Furnishedcheckbox
☑ 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
16.2 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.
16.3 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.
Operator Training Periodrange
hours
24816