Circuit breaker size for motor

[Fluke631]

Hey All,

I am in the process of buying a new air compressor and the manual doesn't state the size of the circuit breaker I need. I have attached a picture of the motor information. Also I would like to know the wire size if I need 25 feet of wire.

Thanks

 

[bxray]

The motor rating is 21.5 amps so 30 amp breaker and #10 wire would be the minimum. You can put a 40 amp and #8 wire.

 

[Fluke631]

Thank you! I already have a free 30 amp breaker so I'll wire it to that one!

 

[War Eagle]

First off I am not an electrical engr or an electrician.

When I built my house In did the wiring and was taught by an electrician the following:

circuit breaker was sized so that the expected load on a circuit was only to be 80% of the breaker capacity. So if the expected load was expected to be 20 amps then the braker size would be 25amps.

So in your example your expected load is 21+ amps at 230 volts you would sized the breaker at 30 amps in order to comply with the 80% requirement.

Also for the wire size you would use #12 wire for 20amp circuit and #10 wire for a 30amp circuit.

So I think that #10 wire and 30amp breaker rated for 230 volts would do your job.

However, I would default to an electrician or electrical engineer if they were to provide you a different recommendation.

 

[RCW]

For giggles, I'd run #8 wire. Never know if that might run a welder later on....

Difference is minimal.

 

[Fluke631]

For giggles, I'd run #8 wire. Never know if that might run a welder later on....

Difference is minimal.

Ya I've got a spool of 8/3 that's what I am going to use

 

[RCW]

Ya I've got a spool of 8/3 that's what I am going to use

Yeah -- when I did a subpanel years ago, the double-poles were short and 8 THHN, just in case.

 

[GreensvilleJay]

I used 'welder' plugs and receptacles for my air compressor and welder. Allows me to put welder anywhere in garage. Also made an adapter to test stoves and dryers in the garage. I get 'volunteered' to fix them 1-2 times a year so it was worth making up the adapters.

 

[Fluke631]

I used 'welder' plugs and receptacles for my air compressor and welder. Allows me to put welder anywhere in garage. Also made an adapter to test stoves and dryers in the garage. I get 'volunteered' to fix them 1-2 times a year so it was worth making up the adapters.

Funny, because I do the same thing! My heaters welders generators are all on welders plugs for easy swaps!

 

[RCW]

I used 'welder' plugs and receptacles for my air compressor and welder. Allows me to put welder anywhere in garage. Also made an adapter to test stoves and dryers in the garage. I get 'volunteered' to fix them 1-2 times a year so it was worth making up the adapters.

Jay - I did just a couple, welder and dryer. One welder, other Compressor.

One thought was a "back-feed" connection for a portable generator also through one. Just haven't made the connecting cable....

I never did get a big compressor, so I probably should think of something better to do with that extra 220v plug...

 

[dochsml]

As a few others have already said, 30A would be the minimum. I didn’t see or maybe missed the LRA for that motor, but I would bet it is a lot more than the 40A that some are suggesting. So, you should be fine either way.

 

[Ping]

Remember, the circuit breaker is there to “protect” the wiring downstream. 30 amp breaker with #8 AWG wire should provide years of trouble free service.

 

[KennysNewFarm]

60 amp circuit breaker with min 10 gauge is preferred but I’d run 8. I work on these everyday. Incoming rush will take a motor out if not properly sized.

 

[dochsml]

60 amp circuit breaker with min 10 gauge is preferred but I’d run 8. I work on these everyday. Incoming rush will take a motor out if not properly sized.

If you put a 60 amp circuit breaker, the wire size should be 6 gauge (or larger).

 

[KennysNewFarm]

If you put a 60 amp circuit breaker, the wire size should be 6 gauge (or larger).

Look up the slide rule, I am not here to argue. My slide rule has always been good for reference. But I sure would not run a 30 amp breaker on a 24.4 FLA Motor.

 

[dochsml]

Look up the slide rule, I am not here to argue. My slide rule has always been good for reference. But I sure would not run a 30 amp breaker on a 24.4 FLA Motor.

I don't disagree. Just need to make sure the wire is sized appropriate to the breaker that is being used and that the breaker is not so large as to exceed the locked rotor amperage. I don't know what that is (but I'm sure it could be looked up for this motor). I'm sure it is ~100A though. So, yeah, a 60A breaker would be perfectly fine as long as the wire is sized appropriately for that size breaker.

 

[War Eagle]

Look up the slide rule, I am not here to argue. My slide rule has always been good for reference. But I sure would not run a 30 amp breaker on a 24.4 FLA Motor.

Not sure where the 24.4 amp reference came from, as it looks like the label says it's a 21.5 FLA motor.

 

[dochsml]

Not sure where the 24.4 amp reference came from, as it looks like the label says it's a 21.5 FLA motor.

I saw that, but didn't mention anything. 24.4 x 1.25 (for breaker sizing) would take it over 30 amps though. Maybe meant 22.4A which would be close if the voltage was 220 instead of the 230 from the nameplate. At 21.5 or 22.4, a 30A breaker with the correct trip curve for a motor (probably D trip curve) would suffice. But, going 40, or 50, or 60 should not be a problem as well. As long as the wire is sized accordingly and as long as it doesn't exceed locked rotor current.

 

[KennysNewFarm]

Not sure where the 24.4 amp reference came from, as it looks like the label says it's a 21.5 FLA motor.

Look at the data tag again. Every electric motor has service factor amp ratings. This motor uses a 1.15 Service Factor. 21.5 x 1.15 service factor equals 24.725 but the manufacturer put 24.4 on the data tag. Listen guys I have been working on compressors for 15 years. I have seen and heard it all. My experience in the field reveals to me most people use bare minimum wire and breakers that have caused numerous failures. Small wire causes voltage drop during start up. All I stated earlier is a recommendation from what I see everyday in the field. Just yesterday on a min max voltage test a compressor started and voltage dropped from 210 Volts to 157 Volts. The contractors are melted, the machine is blowing fuses, etc. Anyways I felt the OPs original post could use an opinion from the guy who actually works for the compressor company he is referring too. In the end the warranty claim will either be accepted or denied based on the initial installation.

By the way use on T-30 Select and your pump will have a 2 year warranty. And yes they will pull an oil sample.

 

[KennysNewFarm]

I don't disagree. Just need to make sure the wire is sized appropriate to the breaker that is being used and that the breaker is not so large as to exceed the locked rotor amperage. I don't know what that is (but I'm sure it could be looked up for this motor). I'm sure it is ~100A though. So, yeah, a 60A breaker would be perfectly fine as long as the wire is sized appropriately for that size breaker.

I have seen locked motor amps at 100 amps in the past. Seems like a lot from a little motor but it does happen.