Motor question...

[1793]

I don't have a great deal of Motor experience so bare with me, please.

I received a call from a customer today asking about an Air Compressor he has purchased.

I was told the motor was 5hp single phase

The nameplate reads, 208/230 -- 34.00A/32.00A.

My question is how does one size the Branch Circuit for this motor, as stated and with the given information. I've looked over 430 but not sure which section(s) to focus on.

Thanks in advance

 

[infinity]

For the branch circuit you need to use the appropriate table in Part XIV in Article 430. For the overload protection you can use the nameplate based on the supply voltage. {430.6(A)(1) & (2)}

 

[neceltic]

Use Table 430.52 to size the short-circuit protective device. 430.22 gives the rules for sizing the conductors assuming a single motor is being fed.

 

[1793]

For the branch circuit you need to use the appropriate table in Part XIV in Article 430. For the overload protection you can use the nameplate based on the supply voltage. {430.6(A)(1) & (2)}

So, Wire size #10 NM Table 430.248 5hp=28
OCP 35A next standard size breaker nameplate 32.00 at 230V

Anywhere close?

 

[augie47]

So, Wire size #10 NM Table 430.248 5hp=28
OCP 35A next standard size breaker nameplate 32.00 at 230V

Anywhere close?

Afraid not...

As noted in Post #3

As far as your circuit conductor, read 430.22(A) 1st sentance.... also, if you are using NM note 334.80

As far as the GFSC protection, read 430.52

 

[1793]

Afraid not...

As noted in Post #3

As far as your circuit conductor, read 430.22(A) 1st sentance.... also, if you are using NM note 334.80

As far as the GFSC protection, read 430.52

Thanks,

I've got to run out for the night. I'll study this some more later and get back with you.

Again, thanks for the guidance.

 

[1793]

Use Table 430.52 to size the short-circuit protective device. 430.22 gives the rules for sizing the conductors assuming a single motor is being fed.

Afraid not...

As noted in Post #3

As far as your circuit conductor, read 430.22(A) 1st sentance.... also, if you are using NM note 334.80

As far as the GFSC protection, read 430.52

OK:
28A * 125% = 35A -- #8 NM Table 310.15(B)(16) Table 430.248 5hp=28A using 430.6(A)(1)

28A * 250% = 70A OCP. 430.52

Any closer?

 

[Bjenks]

When you looked up the tables it seems that you are getting current ratings lower than the rating on the motor. I believe you have to use the larger of the two so in this case you use 32A * 1.25%. The higher number might be because of Table 430.22(E) Verying duty, 15 minute duty cycle rating since it is a compressor.

 

[infinity]

When you looked up the tables it seems that you are getting current ratings lower than the rating on the motor. I believe you have to use the larger of the two so in this case you use 32A * 1.25%. The higher number might be because of Table 430.22(E) Verying duty, 15 minute duty cycle rating since it is a compressor.

Do you have a code reference?

 

[paul]

http://www.mikeholt.com/mojonewsarc...s-Motor-Circuits-and-Controllers~20031126.htm tells the story pretty good.

 

[Bjenks]

Do you have a code reference?

In 430.22 (A) and (E), please note the word "Not less than" meaning if it is a higher load you need to go to a larger conductor. These are only minumums so when a guy replacing a motor with a new motor without any engineering won't burn out the wire if it is less efficient. Most motors that I put a probe to almost always draw less than the tables.

 

[tom baker]

That is a very large single phase motor!
Do not get concerned about the relationship between the motor branch ciruit size and the "circuit breaker" size.
The motor branch circuit is sized per the NEC table size x 1.25, 10 AWG
The motor branch circuit, short circuit and ground fault protecion device "circuit breaker is sized much larger than the motor full load amps to allow it to start, 60 amps per my Sq D Motor Slide Rule
The overloads are sized per the nameplate current, you will pick a heater per the manufacturers instructions.
The overloads protect the motor, the breaker protects the wire.

 

[1793]

That is a very large single phase motor!
Do not get concerned about the relationship between the motor branch ciruit size and the "circuit breaker" size.
The motor branch circuit is sized per the NEC table size x 1.25, 10 AWG
The motor branch circuit, short circuit and ground fault protecion device "circuit breaker is sized much larger than the motor full load amps to allow it to start, 60 amps per my Sq D Motor Slide Rule
The overloads are sized per the nameplate current, you will pick a heater per the manufacturers instructions.
The overloads protect the motor, the breaker protects the wire.

28A* 125% = 35A Table 430.248 5hp=28A using 430.6(A)(1)

28A * 200% = 56A Table 430.52 Note 3

Wire size #8 for NM per 334.80 Table 310.15(B)(16)
OCP 60A

Thanks