Confusion Regarding OCP for Motor Feeder ckt.

[Davisteam]

I have a Lift Station with Two, 3phase, 240v, 3hp pumps with 8.9FLA (Nameplate) each. Coming from the meter, there is a 60amp fusible disconnect. Three 6AWG from the disconnect feeds to a Terminal Block in the Control Panel next to the disconnect. From the Terminal Block, Two Sets of 10AWG feed Two 20A Breakers for Branch Ckt. OCP.

Is it ok for the Feeder OCP to be 60amp and 6AWG Feeder Conductor? My calculation says it should be 25amp with 12AWG Feeder Conductor. What am I missing?
Would it be different if it were a breaker?

 

[kwired]

I have a Lift Station with Two, 3phase, 240v, 3hp pumps with 8.9FLA (Nameplate) each. Coming from the meter, there is a 60amp fusible disconnect. Three 6AWG from the disconnect feeds to a Terminal Block in the Control Panel next to the disconnect. From the Terminal Block, Two Sets of 10AWG feed Two 20A Breakers for Branch Ckt. OCP.

Is it ok for the Feeder OCP to be 60amp and 6AWG Feeder Conductor? My calculation says it should be 25amp with 12AWG Feeder Conductor. What am I missing?
Would it be different if it were a breaker?

Motor needs to use NEC tables for FLA - 3 hp @ 240 volts three phase is 9.6A. You need minimum feeder conductor based on 1.25% largest motor plus all other motos = 21.6 amps. 12 AWG is Ok presuming you have 75C terminations.

Could be on a 35 amp breaker before it has to not hold during starting before you increase it AFAIK, I'd bet most instances a 25 amp breaker holds though.

 

[Davisteam]

Motor needs to use NEC tables for FLA - 3 hp @ 240 volts three phase is 9.6A. You need minimum feeder conductor based on 1.25% largest motor plus all other motos = 21.6 amps. 12 AWG is Ok presuming you have 75C terminations.

Could be on a 35 amp breaker before it has to not hold during starting before you increase it AFAIK, I'd bet most instances a 25 amp breaker holds though.

My mistake about the 9.6 (I was thinking of overload). This was specced out at a 60amp fusible disconnect. I just don't understand. There isn't much more of a load except for the controls, which includes relays, a .75kva transformer, and an Omnisite Box (which only communicates alarm conditions to my cell phone).

Is the Feeder OCP only protecting the Feeder Conductors at this point? If so, I guess it wouldn't matter that they are 60amp and 6AWG.

 

[augie47]

It sounds to me that your 20 amp breakers are protecting your motors. The feeder could be sized less than 60 amps but the conductor is large enough that it is adequately protected so there's no real foul. Is there any nameplate data on the assembled controller ?

 

[Davisteam]

It sounds to me that your 20 amp breakers are protecting your motors. The feeder could be sized less than 60 amps but the conductor is large enough that it is adequately protected so there's no real foul. Is there any nameplate data on the assembled controller ?

Yes, the 20a Breakers protect the pumps from short circuit and ground fault. But I thought the Feeder OCP also was to protect the motors not just the Feeder Conductors?

Not sure what you mean by "assembled controller".

 

[kwired]

Yes, the 20a Breakers protect the pumps from short circuit and ground fault. But I thought the Feeder OCP also was to protect the motors not just the Feeder Conductors?

Not sure what you mean by "assembled controller".

Feeder overcurrent device protects feeder conductors from overcurrent.

Branch circuit overcurrent protection protects the branch circuit conductors from overcurrent.

With motor circuits the overcurrent protection devices is usually only protecting against short circuits and ground faults, they often are higher than conductor ampacity to allow for surge current during motor starting.

The motor overload protection protects the motor from overcurrent due to overload conditions, and subsequently protects the conductors from overload as well which is why you can see a 12 AWG conductor on a 35, 40 even a 50 amp breaker for motor circuits at times.

 

[Davisteam]

Feeder overcurrent device protects feeder conductors from overcurrent.

Branch circuit overcurrent protection protects the branch circuit conductors from overcurrent.

With motor circuits the overcurrent protection devices is usually only protecting against short circuits and ground faults, they often are higher than conductor ampacity to allow for surge current during motor starting.

The motor overload protection protects the motor from overcurrent due to overload conditions, and subsequently protects the conductors from overload as well which is why you can see a 12 AWG conductor on a 35, 40 even a 50 amp breaker for motor circuits at times.

Thank you!

 

[victor.cherkashi]

Yes, the 20a Breakers protect the pumps from short circuit and ground fault. But I thought the Feeder OCP also was to protect the motors not just the Feeder Conductors?

Not sure what you mean by "assembled controller".

I always thought that wiring between OCP and fixed equipment (like: lift controller, motor controller, AC unit, water heater, etc) is clarified as "branch circuit".
am I wrong?

Sent from my ONEPLUS A6013 using Tapatalk

 

[augie47]

Yes, the 20a Breakers protect the pumps from short circuit and ground fault. But I thought the Feeder OCP also was to protect the motors not just the Feeder Conductors?

Not sure what you mean by "assembled controller".

An assembled controller would be something like:

 

[kwired]

I always thought that wiring between OCP and fixed equipment (like: lift controller, motor controller, AC unit, water heater, etc) is clarified as "branch circuit".
am I wrong?

Sent from my ONEPLUS A6013 using Tapatalk

Art 100:

Branch Circuit.
The circuit conductors between the final overcurrent device protecting the circuit and the outlet(s).

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.

Your examples above are conductors within the branch circuit definition.

The line can get a little blurry at times, but a feeder will not connect to the "outlet(s)", it will supply additional "branch circuits" or even other "feeders". A branch circuit will supply "outlet(s)"