Choosing the Right Transfer Switch

Generator transfer switch gear come in different varieties, so our goal here is to keep it simple to help you make an informed decision when choosing a transfer switch for your new home standby generator.

Transfer switches can be manual or automatic. Manual switches are geared for portable generators. After a portable generator has been setup and running, away from door and window openings, the transfer switch is then manually switched on to receive power from the generator.

Homeowners investing in an Automatic Standby Generator will need an Automatic Transfer Switch, or ATS.

The ATS monitors incoming utility power and instantly senses a voltage drop or complete power loss. In either case, the ATS sends a startup command to the connected standby generator. Within mere seconds, the generator engine starts and begins energizing connected circuits.

Likewise, when utility power is finally restored and remains steady for at least 3-5 minutes, the ATS automatically switches from generator power to utility power. Your generator may continue to run for several minutes for the engine cool-down procedure before shutting down.

What Size ATS Do You Need?

As you peruse the Buckeye Power Systems website, you will find transfer switches in sizes ranging from 100-600 Amps and larger. Match the size of the ATS to the size of the main breaker panel(s) being connected.

Here’s how you do it.

Go to your circuit breaker panel and look for the size of the Main Breaker (see illustration below).

200-Amp Main Breaker Panel

Service Entrance Rated ATS or Non-Service Rated ATS?

The Main Breaker panel(s) are typically located at or near the utility meter or “service entrance”. Smaller homes requiring just one Main Breaker Panel is typically 200-Amp service. Larger homes might have two or more 200-Amp panels. So, a home with two 200-Amp panels has 400-Amp Service. A home with three 200-Amp panels has 600-Amp service.

For homeowners seeking Whole House generator coverage, a 200-Amp Service Entrance Rated ATS will be required for each 200-Amp panel.

Here's an image of 200-Amp Service Entrance Rated ATS (note the Main Breaker on the ATS). Presence of a Main Breaker on an ATS makes it Service Entrance Rated.

Cummins RA200 Service Entrance Rated ATS

A 400-Amp ATS can also be connected to the two 200-Amp main breaker panels, however, the cost of two 200-Amp panels is considerably less than the cost of a single 400-Amp ATS. Buckeye Power Systems recommends using a 400-Amp ATS when there is not enough exterior wall space to mount two 200-Amp switches. There are other applications, but most homeowners find using a 200-Amp switch for each main breaker panel makes the best economic sense.

Homeowners seeking to cover Just the Essentials might have two or more 200-Amp Main Breaker Panels but only need to power circuits on just one of the two panels. So, a single 200-Amp Service Entrance Rated ATS will do the job.

Buckeye Power Systems recommends the Cummins RA Series Switches which are compatible with Cummins RS (ex. RS20A air-cooled or RS30 liquid-cooled, and RX Series (ex. RX30, etc.) generators.

When to use a Non-Service Rated ATS

Non-Service Rated ATS gear is used when connecting to Sub-Panels. Sub-Panels do not have a Main Breaker. The circuit breaker feeding electricity to a Sub-Panel is found on a Main Breaker panel located at the Service Entrance. For example, a 200-Amp Main Breaker Panel might have a 60-Amp or 100-Amp circuit breaker feeding electricity to the Sub-Panel.

So, if all your Essential Circuits are located on the Sub-Panel and fed from a 100-Amp breaker (located at the service entrance), use the Cummins 100-Amp, RA Series, Non-Service Rated ATS to provide power to the Sub-Panel.

The illustration below might help.


Image illustrating ATS options

Single-Phase and 3-Phase Switches

Most homes are wired 120/240 Volt Single-Phase and all Cummins RA Series Switches are for residential applications. 3-Phase switches come in a variety of voltages and primarily geared for commercial and industrial applications.

In very rare circumstances, some homes might have 120/240V 3-Phase service for air conditioning circuits and 120/240V Single Phase circuits for the remainder of the house. In such rare instances, the homeowner receives two (2) electric utility bills; one for the single phase service and the other for the 3-Phase service.

If your home receives just one electric utility bill, your home is wired for 120/240V Single Phase service.

We understand the topic of transfer switches might be confusing to some. We get it. Please feel free to call Buckeye Power Systems at 901-379-8097 and a representative will be happy to go over it with you in more detail.

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Click here to view: Cost-Saving Options on Generator Placement Location.