Automatic Transfer Switch (ATS)

A Transfer Switch is an electrical switch that reconnects electric power source from its primary source to a standby source. They are usually installed where a backup generator is located, so that the generator may provide temporary electrical power if the utility source fails. In addition to transferring the load to the backup generator, an ATS also commands the backup generator to start, depending on the voltage monitored on the primary supply. The transfer switch isolates the backup generator from the electric utility when the generator is on and is providing temporary power. Isolation of the generator from the distribution system is required to protect the generator from overload, and to prevent accidental energization of the service wiring.

A transfer switch can be set up to provide power to only critical circuits or entire electrical (sub)panels. Some transfer switches allow for load shedding or prioritization of optional circuits, such as heating and cooling equipment.Complex emergency switchgear used in large backup generator installations permits soft loading, allowing load to be smoothly transferred from the utility to the synchronized generators, and back. Such installations are useful for reducing peak load demand from a utility.

Transfer Switch

The Following Animation demonstrates how a Transfer Switch Works