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Discussion Starter · #1 ·
What is the appropriate breaker size for 1Ph, 240v, 3hp motor on #8 wire slightly over 100 ft. from the panel?

Thanks.
 

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but you have to know what to do with the tables. I'll guess it's a fifty amp breaker. this does assume some form of thermal overload downstream of the breaker, which could be a starter or a thermal device integral to the motor.
 

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i was wrong it's a 45 amp. :whistling2:
 

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future sparky
you had the right table for amperage of the motor. then you have to use Table 430.50 for overcurrent protection which says for single phase motor and inverse time breaker the protection can be up to 250% of the T.430.248 amperage. Thus 17 amps times 250% = 42.5amps which can be increased to the next standard size. (which is where I blew it), as I didn't look and forgot 45 is a standard size. Standard sizes are found in 240.6(A).

This type of motor circuit and overcurrent sizing question will be found on most all electrical tests you will see as you pursue your electrical career.
 

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I actually knew that but it slipped my mind. An instanteous type breaker is like 800%, isn't it? That would be a damn large breaker. An inverse time breaker would have to be used then (for practical purpose) as you said.

I still wonder if this would be continuous but it looks like #8 wire was actually the right choice and a 45A breaker would be best with the information provided.

Also, thank you for the correction. I have been in school 8 months so you have forgetten more about this trade than I will probably know in the next 4 years lol! If I want to help people I have to be sure to post the correct info. I like the challenge of looking up questions in the NEC (sorry to go a bit off topic.)
 

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...it looks like #8 wire was actually the right choice and a 45A breaker would be best with the information provided....
You could have used a #14 wire on that 45 Amp breaker and still be Code compliant on such an installation.
 

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Discussion Starter · #9 ·
NEC T430.248 says 17 amps. Will this motor be used over 3 hours at a time?
Continously - no, this is for a table saw in my personal shop. I picked the #8 wire because it is an approx. 100 ft. run. I was think that the breaker was either to be 20 or 30. As you may have noticed, the answers are over quite a range. Thanks!
 

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What is the appropriate breaker size for 1Ph, 240v, 3hp motor on #8 wire slightly over 100 ft. from the panel?

Thanks.
If this motour start up unloaded then 20 amp breaker will handle very nice but if air compressour please look at the nameplate to verify if it did show the actual HP rating or marked SPL one of the two.

And if you are circuous where to find this code it will show up in NEC art 430. { just becarefull when you use cord et plug attachment they will mention diffrent rules but hardwired then use 430 without issue }

Merci,
Marc
 
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