motor/conductor feeder and branch circuit scgf protection
- Thread starter joethomas
- Start date
- Status
- Location
- Illinois
- Occupation
- retired electrician
First if the circuit is only feeding that stater, it is a branch circuit and not a feeder. The circuit supplying power must have short circuit and ground fault protection. It is not an option. In your case you will need at least #10 copper (assuming 75?C terminations at the breaker and line side of the stater) and you would be permitted to put that on a 70 amp thermal magnetic breaker. This breaker provides the short circuit and ground fault protection for the complete circuit as well as the motor. The overload relay in the stater provides the overload protection for the complete circuit.
PS...all caps is harder to read and is considered shouting.
PS...all caps is harder to read and is considered shouting.
motor/conductor feeder and branch circuit scgf protection
mistake.
Thanks for helping me clear this up. i would appreciate a little more info if you don't mind. I have seen a lot of fused disconnects providing scgf protection and in some cases none or i assumed none. Can you tell me how you determined a 70 amp breaker would be sufficient and do you know if a 60 amp would be ok? I'm feeding two 20hp motors, 3phase,480v with separate circuits in a single conduit for around 150'. These motors are being provided by a company for air blowers and they specified 60amp breakers and they provided the motor controllers with overload protection for each motor. The motors will be approximately the full 150' away from the controllers and the controllers will be right next to the load center (breaker).
Thanks again :thumbsup:
mistake.
Thanks for helping me clear this up. i would appreciate a little more info if you don't mind. I have seen a lot of fused disconnects providing scgf protection and in some cases none or i assumed none. Can you tell me how you determined a 70 amp breaker would be sufficient and do you know if a 60 amp would be ok? I'm feeding two 20hp motors, 3phase,480v with separate circuits in a single conduit for around 150'. These motors are being provided by a company for air blowers and they specified 60amp breakers and they provided the motor controllers with overload protection for each motor. The motors will be approximately the full 150' away from the controllers and the controllers will be right next to the load center (breaker).
Thanks again :thumbsup:
- Location
- Illinois
- Occupation
- retired electrician
The 70 amp breaker is the maximum permitted by the code rules in 430.52. Any breaker smaller than that will meet the code rules, but if it is too small it will trip on the motor starting current.
- Location
- Illinois
- Occupation
- retired electrician
You will have to use larger wire with both motor circuits in the same conduit because of the derating required for more than 3 current carrying conductors. The increase in wire size should also cover any voltage drop issues.
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