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Generac Power Systems



Automatic Transfer Switches

Product Description

Automatic Transfer Switches are an integral part of the power generation process, allowing smooth and immediate transfer of electrical current between multiple sources and the load. When the generator is operating, the transfer switch prevents 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 transfer switch senses when utility power is interrupted, and starts up the generator if the utility power remains absent. In about five to ten seconds, when the generator is producing full power, the transfer switch disconnects the load from the utility and connects it to the generator, restoring electricity to the load. The transfer switch continues 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.

Generac manufactures several types of transfer switches. Each kind operates in a different way, depending upon the requirements of the overall system, and how the load is transferred between the different power sources. Transfer switch types include open transition, momentary closed transition, and bypass isolation

.Generac's automatic transfer switches are designed to be simple to monitor, operate and maintain. All controls needed for daily use are conveniently located on the front door, where bright lamps indicate the switch position. All components are front adjustable and front removable for optimum serviceability. As an extra measure of safety and quality, Generac's transfer switches are UL Listed by Underwriters Laboratories for use in emergency power systems. They are also CSA certified by the Canadian Standards Association.

Generac's expertise in the design and manufacture of automatic transfer switches (ATS) is considerable. The company has produced its own fully instrumented 100 to 2600 amp switches since 1983.

Open transition 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.

Generac's closed transition transfer switches (CTTS) eliminate momentary power interruption 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.

The soft load closed transition switch extends the overlap time to multiple seconds, for a smoother transition of load to the generator. These switches are available in 100 to 2600 amp configurations.

There are many critical systems where interruption of power is not permitted, such as data transmission and hospital care. For those requirements, Generac offers its bypass isolation switch (BIS), which is designed to meet the National Electrical Code's requirements for the inspection and/or maintenance of the automatic transfer switch without the need to interrupt or cut power.

Generac transfer switches are carefully constructed and tested to assure superior performance. By combining them with our own generators, we're able to offer a complete power generation package that we support and warrant.


Some of the outstanding features and benefits of the Generac Automatic Transfer Switches include:

  • UL 1008 listed and CSA certified – Product safety features are recognized by industry organizations
  • 7-day Exerciser Clock – Starts and tests the generator every week, insuring reliable performance when needed
  • In-phase Monitor — Provides instantaneous transfer between two live voltage sources
  • Utility Voltage Sensor – Monitors utility voltage to determine when retransfer of load can occur
  • Line Failure Sensing – Circuitry monitors all phases of the utility service with dropout and pickup points
  • Utility Interrupt Delay – Adjustable timer overrides momentary line failure
  • Engine Warm-up Timer – Adjustable timer allows engine to operate at no load before the transfer switch transfer the load to the generator set
  • Engine Warm-up Bypass – A switch allows the transfer switch to transfer the load to the generator as soon as the preset voltage and frequency levels are reached
  • Minimum Run Timer – Determines the shortest period of time the generator will run and ensures adequate exercise periods
  • Return to Utility Delay – Adjustable timer keeps the load on the generator set until a stable utility line is present
  • Engine Cool-down Timer – Adjustable timer allows the engine to run at no load after the transfer switch transfers the load back to the utility line
  • Frequency and Voltage Set – Sets the minimum frequency and voltage required before the transfer switch will be allowed to transfer the load to the generator set.

Optional Equipment

  • Logic System Control — Fully adjustable timer settings. LED indication for system status and simple field service
  • NEMA Enclosures — NEMA 3R, NEMA 4, NEMA 4X and NEMA 12
  • Quick Change, Multi-Voltage Panel — Multiple phase / voltage configurations with a single switch. Available on switches up to 400 amps
  • Auxiliary Contacts — One SPDT is standard. Additional sets are available
  • Programmable Exerciser — Permits selection of  "days of the week" and "time of day." Visible digital chronograph used to select times. Allows exercising from one to seven days a week
  • Exterior Meter Package — Enables user to monitor the system parameters with the door closed
  • Fourth Pole — Fourth pole for switching the neutral conductor
  • Preferred Source Selector Switch — Ability to select which power supply will be considered the normal source
  • Manual Selector Switch — 3 positions: normal, automatic and standby
  • Manual "Return to Normal" (electrically operated) — Ability to select when the switch will transfer back to normal
  • Remote Automatic Control Circuit — Ability to start the generator and transfer the load to emergency from a remote location
  • Signal before Transfer Contacts — Adjustable from 0.1 – 10 seconds. Signals to special loads prior to transfer. Often used to prevent elevators from stopping between floors
  • Generator Mounted Transfer Switch — Transfer switch may be mounted on the genset for both indoor and outdoor application.








































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