Circuit Breaker Sizing for Your Home’s Generator

Did you recently buy a generator for your home but now you’re wondering what size circuit breaker you need for it?

Here’s what you need to know: The circuit breaker for your generator should be sized according to the generator’s output (in amps). We’ll show you exactly how to calculate this output below.

First, though, let’s take a look at why your generator needs a circuit breaker in the first place.

Note: Some generators come with overload protection installed within the device itself and may not require circuit breakers. To determine whether your circuit breaker has built-in protection, contact the manufacturer or look up the generator model online.

Want to skip the calculations and have a professional install the correctly sized breaker? Just contact us and we’ll do all the work for you.

Why does my generator need a circuit breaker?

A generator without a circuit breaker will live a shorter life and can even start an electrical fire.

Here’s why: When appliances draw more power than your generator’s designed to provide, it forces an unsafe amount of electricity to course through your home’s wiring. And over time, those wires will overheat and cause a fire.

But circuit breakers prevent that from happening by providing “overload protection” for your generator. A circuit breaker carefully monitors the amount of electricity that flows between your generator and the appliances it feeds. If the level of electricity ever exceeds a safe amount, your circuit breaker will disconnect the load in a matter of seconds.

Now that you know why you need overload protection, let’s take a look at how to determine the right size circuit breaker for your generator.

5 steps to calculating the right circuit breaker size for your home generator

Step 1: Locate the power specifications label on your generator.

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Step 2: On that label, look for the rated current, labeled as “AMP”.

An example of a typical generator’s data label.

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Step 3: On that same label, find the power factor, labeled as “PF” or “PWR Fact”).

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The power factor is the small portion of power that is produced by the generator that doesn’t reach or get “used” by the connected appliances.

This number will always be a number between 0 and 1 (for example PF= .8).

Step 4: Divide your rated current (Amps) by the power factor (PF) to determine your true current value.

Example: If your generator has a rated current of 50 amps with a power factor of 0.8, here’s how you’d calculate your true current value:

50 ÷ 0.8 = 62.5 true current value (in amps)

Step 5: Get a circuit breaker that’s sized between 100% and 125% of the true current value.

Example: If your true current value is 62.5, your generator will use a 70 amp breaker.

Need help sizing your generator’s circuit breaker?

If you have generator questions, we have answers.

Just contact us. We can install your home generator and make sure that you have the right-sized circuit breakers installed as well.

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