The Role of an Automatic Transfer Switch

An automatic transfer switch (ATS) is a critical component of the emergency power supply system for any facility. The automatic transfer switch selects a power source, either standard utility company-provided power or emergency generator power, and conducts that power to critical loads. There are four basic types of automatic transfer switches: break-before-make (open transition), make-before-break (closed), delayed transition (center off) and solid state switch. An automatic transfer switch should be tested monthly to ensure it will engage properly if an emergency does take place.

Types of Automatic Transfer Switches

Open Transition: The break-before-make automatic transfer switch is the most common type of switch. The electrical load will be interrupted during the shift from the normal source to the emergency source.

Closed Transition: The make-before-break automatic transfer switch allows a “hot-to-hot” transfer without the loss of the critical load.

Center Off: The delayed transition automatic transfer switch is most commonly used for large inductive loads. The delayed transition allows for magnetic fields to collapse before reconnection.

Solid State: A solid-state automatic transfer switch relies on transistor technology, sub-cycle transfers. While there is technically a break in the load current, these units work at such a rate of speed, it will avoid damage to sensitive equipment.

Testing an Automatic Transfer Switch

Every installed automatic transfer switch should be tested monthly. The test should include an automatic generator start initiated by the transfer switch, as well as an automatic transfer to the standby generator. These monthly tests will not affect the life-span of the automatic transfer switch.

The Automatic Transfer Switch

The automatic transfer switch is an incredibly important part of the electrical system of any facility. It helps to ensure that critical systems will stay online in case of a critical electrical failure. While it can be scary to engage and test, the automatic transfer switch should be tested monthly to identify and resolve any potential issues that could keep the switch from working properly in case a real emergency takes place, which is not the time to find out if the switch is working properly.