sizing control panel feeder breaker

[mjmike]

We are designing the power feed to a small control panel. It is a skid mounted pumping system that includes 2 small pumps and the control panel all pre-wired. The control panel has an integral non-fused disconnect (30A-3P). The manufacturer indicates the full load amps are 5A at 480V-3phase. We asked them for the recommended overcurrent protection device (feeder breaker). They indicated to size per the NEC which always seems to be the easy way out for a manufacturer. This would most likely be considered an industrial control panel where 409.21.C would be the rating of the breaker. However, it appears you can't go by FLA of the panel, but need individual load ratings. Not sure where to go to calculate the proper breaker size.

 

[JoeStillman]

Take a look at 430.53(C)(4). If the calculated size of the OCPD is less than the ampacity the supply conductors, you may use a breaker rated for the conductors instead. If the whole skid is only 5A and the pumps are equal size, the maximum inverse-time breaker you could use would be around 12A (table 430.52). But if you are feeding the skid with #12 wire, you can feed it from a 20A breaker.

 

[petersonra]

Take a look at 430.53(C)(4). If the calculated size of the OCPD is less than the ampacity the supply conductors, you may use a breaker rated for the conductors instead. If the whole skid is only 5A and the pumps are equal size, the maximum inverse-time breaker you could use would be around 12A (table 430.52). But if you are feeding the skid with #12 wire, you can feed it from a 20A breaker.

You are never required to use smaller than a 15A CB.

 

[mjmike]

Take a look at 430.53(C)(4). If the calculated size of the OCPD is less than the ampacity the supply conductors, you may use a breaker rated for the conductors instead. If the whole skid is only 5A and the pumps are equal size, the maximum inverse-time breaker you could use would be around 12A (table 430.52). But if you are feeding the skid with #12 wire, you can feed it from a 20A breaker.

Not following this logic. We are specifying a single-point electrical connection to the control panel. All else is pre-wired. the pumps are the same size. I don't think this is really a group installation. I think a group installation would be say a circuit to a wireway that taps down to multiple motors and say a unit heater.

 

[mjmike]

You are never required to use smaller than a 15A CB.

I am assuming this is based on 240.6.A?

 

[JoeStillman]

Not following this logic. We are specifying a single-point electrical connection to the control panel. All else is pre-wired. the pumps are the same size. I don't think this is really a group installation. I think a group installation would be say a circuit to a wireway that taps down to multiple motors and say a unit heater.

What would you call the circuit feeding the panel? Is it a feeder or a branch circuit? I contend that it is a feeder because there are overcurrent devices on the load end (the motor overloads.) If it's a feeder, it's a multi-motor feeder, and falls under 430.53.

 

[mjmike]

What would you call the circuit feeding the panel? Is it a feeder or a branch circuit? I contend that it is a feeder because there are overcurrent devices on the load end (the motor overloads.) If it's a feeder, it's a multi-motor feeder, and falls under 430.53.

After the non-fused disconnect in the panel, it feeds 2 motor breakers, control transformer fuses, and a surge suppress with no OCPD.

 

[JoeStillman]

After the non-fused disconnect in the panel, it feeds 2 motor breakers, control transformer fuses, and a surge suppress with no OCPD.

That makes it a feeder.

Feeder. All circuit conductors between the service equipment, the source of a separately derived system, or other power supply source and the final branch-circuit overcurrent device.

I referenced the wrong paragraph in 430 before - its 430.63(B);

(B) Other Installations. Where feeder conductors have an ampacity greater than required by 430.24, the rating or setting of the feeder overcurrent protective device shall be permitted to be based on the ampacity of the feeder conductors.

 

[mjmike]

That makes it a feeder.



I referenced the wrong paragraph in 430 before - its 430.63(B);

Thanks, I will review. In the meantime, I got the mfgr to supply a thermal mag main disconnect in the panel which I will just match for my feeder.