Why Does My Automatic Transfer Switch (ATS) Have a Larger Breaker Than My Generator Breaker?

Jun 26, 2023
Knowledge

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Why-Does-My-Automatic-Transfer-Switch-ATS-Have-a-Larger-Breaker-Than-My-Generator-Breaker

Public Answer

ATS Breakers

A generator’s main breaker is sized to handle the rated amperage of the generator and is intended to protect the generator from being overloaded. When using a whole house transfer switch the transfer switch amperage should match the amperage rating of the panel that it is protecting.

Example: When using a whole house service entrance-rated transfer switch to protect a 200A service, the transfer switch will also need to be rated for 200A, regardless of what size generator is being used (unless the generator's amperage exceeds the amperage of the transfer switch). However, some loads may need to be managed if using a generator with a lower amperage rating than supplied to the home. A dealer will be able to properly size a generator and advise if any load management is necessary.

Note: Most applications do not require the generator amperage to match the utility service amperage provided to the home. This is because most homes will not pull the max amperage supplied by the utility even if all appliances were to be turned on and used simultaneously.

If a generator capable of 200A at 240V is truly needed, the power formula (volts x amps = watts) can be leveraged to roughly determine how many watts the generator must be rated for.

For example: 240V x 200A = 48,000W

Again, most residential applications do not require a generator this large. A dealer is able to properly size the generator for a specific application, which is highly recommended.

Note: Breakers will have a MAX rating. You can always pull less than the max, but you cannot pull more than the max. Trying to pull more amperage through a breaker than what it is rated for will result in the breaker tripping.