OCPD for motor

[jph320]

50 hp 480v motor. breaker size? debate is FLC x 125% or 250%

 

[jph320]

we are trying to size the breaker that will feed directly into the new compressor. 480v 50hp.

 

[augie47]

Does the new compressor have a control panel ? starter ? name tag ? or just a motor ?
If it has a control panel there should be information as to the supply power.
You need to assure the motor will have both overload and SC-GF protection.
If it's a package unit often the manufacturer will specify the protection required which at times can be fusible protection.

 

[petersonra]

we are trying to size the breaker that will feed directly into the new compressor. 480v 50hp.

have you considered looking at the applicable code sections, mostly to be found in article 430?

Part IV starting at 430.51 would appear to answer your question.

ETA.

I don't understand the 125% or 250% comment, or what "directly into the compressor" means.

As another poster mentioned it is possible it already has branch circuit protection. If it does, then this is a motor feeder and your answer will be found in Part V starting at 430.61.

 

[jph320]

name plate says FLA 67. so what size breaker to I feed it with? in sect 430, I understand it to read OCPD 125%

 

[david luchini]

name plate says FLA 67. so what size breaker to I feed it with? in sect 430, I understand it to read OCPD 125%

See Table 430.52. It lists 250% for most Inverse Time breaker applications.

 

[Smart $]

name plate says FLA 67. so what size breaker to I feed it with? in sect 430, I understand it to read OCPD 125%

Compressor of what? Air, refrigerant, other gas?

Compressor motors are typically controlled, i.e. start/stop. Compressors manufactured and sold as a listed unit (controller, motor, compressor) are required to list electrical supply circuit requirements on the unit nameplate (i.e. disregard actual motor nameplate). What are those values?