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Automatic Generator Transfer Switches

Automatic generator transfer switches are essential to the power generation process. They allow the smooth and immediate transfer of electrical current between multiple sources and the loads. An automatic generator transfer switch senses the loss of utility power and automatically starts up the generator and transfers the load to it. When utility power is restored, it switches the load back to the utility, and shuts down the generator. When the generator is operating, the generator transfer switches prevent dangerous feedback of current to the utility’s system. It also ensures that different power sources are fully synchronized before their power is combined or loads are transferred, which is imperative for safe operation. The generator transfer switches continue to monitor utility power, and when it is restored, switches the load from the generator back to the utility. Once the generator is disconnected, it goes through a cool-down routine and is automatically shut down.

Your ASNE representative can help you pick the generator transfer switch that best fits your application. Depending on the requirements of your system and how the load is transferred between the different power sources there are different types of generator transfer switches to choose from. Transfer switch types include open transition, momentary closed transition, and bypass isolation.

Open transition generator transfer switches are the simplest kind, and are mechanically interlocked. They disconnect the load from one power source before making the connection to the other. This switch is suitable for emergency and prime power applications without modifications.

It meets rating requirements of article 700, 701, and 702 of the National Electric Code, C.S.A. and UL 1008.

  • Sizes: 100 -2600 Amps
  • Poles: 2, 3, or 4
  • Enclosures: NEMA 1, 12, 3R, 4X

Generac’s closed transition generator transfer switches (CTTS) eliminate momentary power interruption during transfers when both sources are present and synchronized, by transferring the loads with an overlapping contact arrangement. The momentary closed transition switch transfers the power within one hundred milliseconds, which does not require utility protective relaying. This transfer switch is suitable for use on emergency and standby systems, transfer of total system load, 100% equipment rated, both inductive and resistive.

  • Ratings from 100 to 2600 AMP
  • 3 or 4 pole 600 VAC contractors
  • NEMA 1, 3R, 4, 4X and 12 enclosures
  • UL 1008 listed at 480 VAC

Complies with:

  • NFPA 70, 99, 101, 110
  • NEC 517, 700, 701, 702
  • IEEE 446, 241

Generac’s bypass isolation switch (BIS) is ideal for critical systems where interruption of power is not permitted, such as air traffic control, emergency communications, and hospital care. For this type of application Generac offers its 400 Amp bypass isolation switch that consists of both an automatic transfer switch, and a bypass isolation switch. This design provides a means of directly connecting load conductors to a power source and isolating the transfer switch in order to permit maintenance and testing of the transfer switch with no interruption to the load. This UL1008 listed switch is designed to meet the National Electrical Code’s requirements for inspection and/or maintenance of the automatic transfer switch without the need to interrupt or cut power.

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