How to Order an Automatic Transfer Switch (ATS)

Automatic Transfer Switch (ATS)

Automatic transfer switches are a critical component of an emergency standby system. Available in sizes ranging from 30A through 5000A, Global Power Supply provides reliable, sturdy, versatile and compact ATS that transfer essential loads and electrical distribution systems from one power source to another.

The following are some important factors to consider when ordering an ATS.

Service Entrance Rating

The utility requires a service level entry to the building. The backup power system designer will define the power requirements for the building and determine in the design whether the ATS will be the service level entry, or whether a distribution switch will be used.

Bypass Isolation Switch

A bypass isolation switch in an ATS is an option for power requirements that must not go down during maintenance procedures. A bypass isolation switch consists of 2 switches and 1 cabinet, the main switch can be drawn out for maintenance, while the bypass carries power to facility. This is especially important for applications such as hospitals and data centers.


The power system designer defines the number of poles used in an ATS. A three phase backup power system can be 3-pole or 4-pole, with the deciding factors being the schematics of the power system and its coordination with ground fault protection.

Enclosure Type

The type of enclosure needed is largely decided by the location of the ATS. The decision is usually between indoor (NEMA 1R) and outdoor rated enclosures (NEMA 3R). In general, outdoor enclosures are more expensive and take up more space than indoor enclosures.


The current rating on an ATS switch (in Amps) needs to be at least as large as the generator capacity or the normal circuit capacity that’s brought to the switch, whichever is larger.

For assistance on your power generation project please contact our team of power experts today.