Derating with motor loads

[augie47]

Other than being covered in Annex B when applying the derating factors for conduit fill is it permissible to use actual load (Table FLA) values :?
For example, you have (5) motors each with 10 FLA on 25 amp breakers. NEC allows #14 conductors. If all 5 are fed thru one conduit, 15 conductors #14 derates to
12.5 amps. O.K. by Code to use the FLA of 10 amps X 1.25 ??

 

[petersonra]

Other than being covered in Annex B when applying the derating factors for conduit fill is it permissible to use actual load (Table FLA) values :?
For example, you have (5) motors each with 10 FLA on 25 amp breakers. NEC allows #14 conductors. If all 5 are fed thru one conduit, 15 conductors #14 derates to
12.5 amps. O.K. by Code to use the FLA of 10 amps X 1.25 ??

I am not sure what you are asking.

Conduit fill is strictly about how much of the conduit is sued up.

 

[BillyMac59]

If your asking can you derate based on load - no.

 

[don_resqcapt19]

You are not really using the load as part of the ampacity adjustment process. You are simply applying the 50% adjustment and getting a new ampacity for the conductors in the raceway.

This is a motor application so the conductor sizing and OCPD is based on the rules in Article 430. The minimum ampacity of the motor branch circuit conductors for a motor with a table full load current of 10 amps is 12.5 amps and the maximum branch circuit short circuit and ground fault protective device for that motor is 25 amps. Your installation is compliant with the code assuming that the motor full load current was taken from one of Tables 430.247 through 430.250, and not from the motor nameplate.

 

[drktmplr12]

the process is as follows:

1. calculate minimum ampacity of branch circuit for multi motor circuit from NEC tables
2. select conductor size and OCPD
3. derate
4. reselect conductor size if needed

nameplate amps never enter the equation unless high torque/inertia load or low rpm motor