Compressor Wire Size???

[Graham08]

I searched and found conflicting information, so I figured I would ask again. My situation is that I have a Champion 5 HP compressor that I am converting to single phase with a Baldor 5 HP motor. The nameplate full load amperage is 23 amps.

Going by the method described in other posts:

Full load amps (table, 230V): 28
125% for conductor sizing: 35

From this information, I come up with #10 THHN conductors in conduit (EMT), and at least a 40 amp breaker. Sound right?

When using THHN, I am allowed to use the 90 deg C column in Table 310-16, correct?

Also, is a #12 THHN ground acceptable for this scenario?

 

[Aceman]

I searched and found conflicting information, so I figured I would ask again. My situation is that I have a Champion 5 HP compressor that I am converting to single phase with a Baldor 5 HP motor. The nameplate full load amperage is 23 amps.

Going by the method described in other posts:

Full load amps (table, 230V): 28
125% for conductor sizing: 35

From this information, I come up with #10 THHN conductors in conduit (EMT), and at least a 40 amp breaker. Sound right?

When using THHN, I am allowed to use the 90 deg C column in Table 310-16, correct?

Also, is a #12 THHN ground acceptable for this scenario?

No, you can't use the 90 degree column, use the 75 degree.

#10 ground.

Everything else, you're good to go.

 

[Graham08]

Thanks. That just saved me some bucks, because I have spools of #10 on hand.

 

[pattenp]

A 30A breaker will work.

 

[Aceman]

A 30A breaker will work.

It may, but it's not legal.

 

[pattenp]

It may, but it's not legal.

Okay.. what makes it illegal by having a smaller breaker?

 

[Aceman]

FLC(taken from NEC tables) x 125%=minimum breaker size

28 x 125%=35 amps

 

[pattenp]

FLC(taken from NEC tables) x 125%=minimum breaker size

28 x 125%=35 amps

The 125% is for determining conductor size under 430.22. The allowable max breaker size is set by 430.52. I don't see where having a smaller breaker is disallowed since the wording in 430.52 says the protective device is not to have a rating that exceeds the values in table 430.52. I just don't see where using a 30A breaker is against code in this case.

 

[Aceman]

210.20(A)

Motors are considered a continuous load unless marked otherwise.

 

[pattenp]

210.20(A)

Motors are considered a continuous load unless marked otherwise.

You're the man...Excellent. I just wasn't finding it. I was stuck on overcurrent devices shall not exceed a certain rating related to the conductor size and application.