Automatic transfer switches

An Automatic Transfer Switch (ATS) is a crucial component in a standby generator installation that allows for the automatic switching of electrical loads between the utility power source and the generator.

Operation

When the utility power is interrupted or drops below a preset level, the generator starts and signals the ATS to switch the load from utility to generator power. The generator controller continues to monitor utility power conditions and signals the ATS to re-transfer the electrical load back to utility power when it recognizes the return of utility voltage. Communication is dictated by the generator controller using the N1 and N2 wires for sensing, and the 23 and 194 wires to perform the actual transfer of loads. For more information about generator controller wiring, see the What Is the Purpose of the Generac Home Standby Generator Control Wires? article.

How do I know if my transfer switch is "on"?

• The transfer switch handle is in the UP position when utility is providing power to the home. LOAD terminals (T1, T2) are connected to utility terminals (N1, N2).
• The transfer switch handle is in the DOWN position when power transfer has occurred and the backup generator is supplying power to the home. LOAD terminals (T1, T2) are connected to EMERGENCY terminals (E1, E2).

Important: This image is offered for reference only. Components shown in the image will vary in size and orientation depending on the transfer switch model. For example, 50A switches use a single coil design and the handle position is opposite of the 100A and larger switches. On the 50A switch when the handle is UP the loads are connected to EMERGENCY power. When the 50A switch handle is DOWN the loads are connected to the UTILITY source. It is recommended that you refer to your transfer switch's user manual for more accurate and detailed information.

Maintenance and testing

Regular maintenance and testing of the ATS are important to ensure the reliable and safe operation of the standby generator. Note that during a generator exercise, a transfer of loads does not occur during the exercise cycle unless utility power is lost. To test the operation of a transfer switch, a homeowner can simulate a power outage as described in the How Do I Simulate a Power Outage to Test My Home Standby System? article.

Manually operating an automatic transfer switch

In some cases, such as emergency outages, manually operating an automatic transfer switch may be necessary. This operation is not recommended unless necessary precautions have been taken. See: How do I manually operate an automatic transfer switch?