Motor Supply Sizing

[laketime]

We have a customer asking for us to desing a system for them for the following. It is a 15hp (16.9hp on nameplate I am told) 240/460v 3 phase pump for a sewage airation system. I would like to run it off of 240v three phase as we also need to add lights in this small building housing the pump. I am horrible at motor calculations. What size circuit breaker would we use to feed this and do we need to add in thermal protection with fuses? There is supposedly a control panel coming with this but no word on if it includes heaters. Any help is appreciated.

 

[Jraef]

When you see something like "16.9HP" on a nameplate, it's a clue that the motor is an IEC design, rated in kW and European voltages and currents based on 50Hz operation, then the values are converted to HP at 60Hz operation for North America. The problem that you run into with this is that the NEC requires that you use the Tables in article 430 for determining the FLC to use in selecting conductors, but those tables are not going to show values that are not "normal" HPs. When I have run up against this, AHJs have insisted that you must use the next LARGER value, not the "closest", so in your case you must size the conductors based on the FLC table in the NEC 430.250 as if it were a 20HP 230V motor, 54A.

 

[laketime]

When you see something like "16.9HP" on a nameplate, it's a clue that the motor is an IEC design, rated in kW and European voltages and currents based on 50Hz operation, then the values are converted to HP at 60Hz operation for North America. The problem that you run into with this is that the NEC requires that you use the Tables in article 430 for determining the FLC to use in selecting conductors, but those tables are not going to show values that are not "normal" HPs. When I have run up against this, AHJs have insisted that you must use the next LARGER value, not the "closest", so in your case you must size the conductors based on the FLC table in the NEC 430.250 as if it were a 20HP 230V motor, 54A.

Now as far as overcurrent protection do I multiply that amount by 125%? Really I am bad at this...:dunce:

 

[ptonsparky]

Now as far as overcurrent protection do I multiply that amount by 125%? Really I am bad at this...:dunce:

Most likely the setup will come with overload protection and you would set it to nameplate amperage for 460 60 HZ.

Following Jraef suggestion of 54 amps, the conductors would be sized at 1.25*54.

 

[Jraef]

Most likely the setup will come with overload protection and you would set it to nameplate amperage for 460 60 HZ.

Following Jraef suggestion of 54 amps, the conductors would be sized at 1.25*54.

I think you meat 230V, because that's what he is using. But yes, the OL protection should be set for the actual motor FLA on the nameplate.

Laketime,
If you were referring to sizing a circuit breaker or fuses, then you would use the table 430.250 value.

 

[ptonsparky]

I think you meat 230V, because that's what he is using. But yes, the OL protection should be set for the actual motor FLA on the nameplate.

Laketime,
If you were referring to sizing a circuit breaker or fuses, then you would use the table 430.250 value.

Yes, I did mean 230v. Thank you.