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What Size Breaker for 3.7 Hp Air Compressor & Its Computation

Written by Edwin Jones / Fact checked by Andrew Wright

what size breaker for3.7hpaircompressor

Installing a dedicated circuit for your air compressor is a good idea, especially if you always use it. However, it brings to question, “What size breaker for 3.7 hp air compressor will surely fit in your circuit?”

Professionals sugges that a 3.7 hp compressor requires a 20 amp breaker and not lower. To clear any confusion about breaker sizing, I have prepared a brief explanation below, complete with a guide to proper breaker sizing.

What is the Proper Breaker Size for a 3.7 Hp Air Compressor?

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Using a 20 amp circuit breaker for air compressor with 3.7 hp makes sense. It is enough to support its power needs from start-up up to the long run. Furthermore, it can prevent damaging your unit by faulty circuits. Indeed, proper sizing of the circuit breaker will keep you safe from fire hazards and save energy.

You might encouter manufacturers’ suggestions of using a 15 amp breaker. But, you should not follow this advice.

So, why do many professionals recommend a 20 amp double pole breaker for a 3.7 hp compressor instead of the 15 amp one?

Well, it is much more reliable and safe.

The recommended breaker size by most manufacturers is only measured for the amp rating of their product. They only base the air compressor breaker size on its power rating. However, they forgot to consider the current draw during start-up, where the problem mostly happens.

During start-up, the air compressor’s motor can draw up to 60% of its power rating. Therefore, using a 15 amp circuit breaker for a 3.7 hp compressor won’t be enough for the start-up load.

Using an underrated circuit breaker in a motorized device may result in circuit overloads which cause the circuit breaker to trip. It can also damage your compressor unit by suddenly overheating its motor, bringing a significant risk of fire hazards in your place.

Proper Way to Figure Out the Breaker Amp of an Air Compressor


To correctly figure out the right breaker size you need to use in an air compressor, you must do a short computation.

  • Determine the power wattage of your unit – If your unit is rated as horsepower, you first need to convert it into watts. As you do the research, one hp is equal to 745.7 watts.
  • Let’s take the above unit—a 3.7 hp air compressor—as an example. So, 3.7 hp multiplied by 745.7 watts is equal to 2,759.09 watts.
  • Find out the breaker amp – Now that you got the total wattage of the air compressor, you need to divide it by its voltage requirement to get the suggested breaker amp.

Most air compressors nowadays have a voltage requirement of 230v, and some old units require 240v. You can look at its tag or label to see the voltage requirement of your compressor.

On the other hand, the average household outlet for high-powered electrical tools is 220v. There is no problem with it.

Now that you have an air compressor with a total wattage of 2,759.09 watts and suppose a voltage requirement of 240 v, you will get an amperage of 11.49. According to the computation, a 15 amp circuit breaker is enough to power a 3.7 hp air compressor.

However, as I said earlier, the air compressor’s motor can draw up to 60% of its total power during start-up. In this case, a 15 amp circuit breaker won’t be sufficient to supply the electrical load of a 3.7 hp 240 volt air compressor as it can draw more than 18 amps during start-up.

A 20 amp circuit breaker is the best to use for a 3.7 hp air compressor. Using a 20 amp circuit breaker, you can run your air compressor efficiently, and you don’t have to worry that your unit may overheat or get damaged.

Furthermore, this computation can also be used for a lower type of compressor that only requires 120v of voltage power.

You can watch this video by Muddy Tracks about how he installed a dedicated circuit for his high-powered air compressor in his basement. Look carefully at how he properly runs the wiring to prevent mixing it with other electrical wirings.


Knowing what size breaker for 3.7 hp air compressor will keep your unit working efficiently and free from electrical damage. Furthermore, considering the proper way of computing the device amp and the factors that affect the loads during start-up will help you decide the appropriate breaker size for your circuit.

Now that you know how to figure out the breaker size for a 3.7 hp air compressor, do you think you can size up other air compressor units? Is there anything you want to know about the air compressors? Please leave it in the comment section below so that I can tackle it in another article.

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