15 hp air compressor 3 phase 208 voltage

[bradleymattlin]

I have a question with a 15 hp air compressor. 208 voltage 3 phase. the full load current is 46.2. so for wire size i take it by 125 percent for 57 amps. i can run number 6 thwn/thhn. But for the breaker size i use 250 percent for the inverse time breaker and come up with 115 amps for breaker size. But the maunfacter told me i can put it on a 90 amp breaker and was trying to figure out why is this.

 

[jazer]

the 250% is the maximum allowed by the NEC. Anything lower is permitted and suitable as long as it holds during the start-up in-rush period. I am quite sure the 90 amp breaker will be suffice.

 

[bradleymattlin]

Thanks for the input. i was thinking it had to be that high.

 

[hurk27]

If this is a reciprocal compressor make sure the motor is rated for 208, most I have wired will have a 200 volt rating, I did one where the owner ordered the compressor for 240 volts and it came with a 230 volt rated motor, it lasted about 3 months and burned up, he ordered a 200 volt motor for 208 and it has been running ever since.

High torque motor applications like air compressors are not friendly with 208 unless they are designed for it.

 

[Cow]

If this is a reciprocal compressor make sure the motor is rated for 208, most I have wired will have a 200 volt rating, I did one where the owner ordered the compressor for 240 volts and it came with a 230 volt rated motor, it lasted about 3 months and burned up, he ordered a 200 volt motor for 208 and it has been running ever since.

High torque motor applications like air compressors are not friendly with 208 unless they are designed for it.

I must be missing something, when I wire motors it's always been:

480v supply = 440-460v motor
240v = 230v
208v = 200v

I'm curious why you think you can't run motors that way?

 

[hurk27]

If this is a reciprocal compressor make sure the motor is rated for 208, most I have wired will have a 200 volt rating, I did one where the owner ordered the compressor for 240 volts and it came with a 230 volt rated motor, it lasted about 3 months and burned up, he ordered a 200 volt motor for 208 and it has been running ever since.

High torque motor applications like air compressors are not friendly with 208 unless they are designed for it.

I must be missing something, when I wire motors it's always been:

480v supply = 440-460v motor
240v = 230v
208v = 200v

I'm curious why you think you can't run motors that way?

I'm missing what your trying to say:?

All I was trying to point out is that high torque motor applications like air compressors do not do well when a 230 volt motor is run on 208, a very common mistake, I have run into it a few times, I have seen a 220 volt rated compressor motor run fine on 208, but a 200 volt motor is more common for 208 and much more efficient.

While on the other hand constant torque motor applications such as screw compressors, blowers, fans, and even water pumps seem to do ok on 208 with a 230 volt rated motor just not very efficient.

 

[Cow]

I'm missing what your trying to say:?

All I was trying to point out is that high torque motor applications like air compressors do not do well when a 230 volt motor is run on 208, a very common mistake.

Sure.

240 volts and it came with a 230 volt rated motor, it lasted about 3 months and burned up, he ordered a 200 volt motor for 208 and it has been running ever since.

I read this part and thought you were saying a 230 volt motor wouldn't last on a 240v system but a 200v motor on a 208v system would.....

It was a simple misunderstanding.

 

[hurk27]

Sure.



I read this part and thought you were saying a 230 volt motor wouldn't last on a 240v system but a 200v motor on a 208v system would.....

It was a simple misunderstanding.

No problem, guess I could of worded it better.

I guess I had the OP in my mind and because he was talking about installing this on a 208 volt system I didn't think to mention it in my post:ashamed1: