Feeder breaker selection for two pumps. attachment available

[tahir mehmood]

Number of submersible pumps = 2
Full load amps of each pump = 35.1
connection = star delta.

star contactor = 18 amps

delta contactor = 25 amps

Main contactor = 25 amps

overload = 30 to 40 amps

similarly for the other pump.

main breaker size = 100 amps

calculation for the feeder breaker:

Feeder protection [430.62(A)] isn’t greater than the largest branch circuit ground fault and short circuit protective device plus the other motor FLC.

Branch breaker =
so pump 1 = (35.1 * 2.50) = 87.75 jumping to next size = 100 amps
pump 2= (35.1 * 2.50) = 87.75 jumping to next size = 100 amps

Main feeder breaker = 100 + 35.1 = 135.1 so going down = 125 amperes.

Note:

The branch breaker calculated by the manufacturer is 100 amps, if we apply NEC then it must be 125 amperes for both pumps. i.e. QM in the drawing. kindly clarify .

Feeder which i calculated shall be 125 amperes or some thing else. kindly advise.

 

[david luchini]

Number of submersible pumps = 2
Full load amps of each pump = 35.1
connection = star delta.

star contactor = 18 amps

delta contactor = 25 amps

Main contactor = 25 amps

overload = 30 to 40 amps

similarly for the other pump.

main breaker size = 100 amps

calculation for the feeder breaker:

Feeder protection [430.62(A)] isn’t greater than the largest branch circuit ground fault and short circuit protective device plus the other motor FLC.

Branch breaker =
so pump 1 = (35.1 * 2.50) = 87.75 jumping to next size = 100 amps
pump 2= (35.1 * 2.50) = 87.75 jumping to next size = 100 amps

Main feeder breaker = 100 + 35.1 = 135.1 so going down = 125 amperes.

Note:

The branch breaker calculated by the manufacturer is 100 amps, if we apply NEC then it must be 125 amperes for both pumps. i.e. QM in the drawing. kindly clarify .

Feeder which i calculated shall be 125 amperes or some thing else. kindly advise.

The branch and feeder overcurrent protection should be based on the Art. 430 Full-load current tables, rather than the actual motor full-load current.

The next size up from 87.75A would be 90A, not 100A. But based on the Table value, 100A would likely be OK.

125A sounds like the correct feeder breaker size to me.

 

[Jraef]

That main device in the panel is not a breaker, it's just a non-fused disconnect. Since that is a not a breaker or fuses, the size of your feeder will be dictated by the size of their conductors.

I would use 125% of the largest motor + total remaining FLA; that total is 79A so an 80A breaker would be appropriate, but if the conductors are good for 125A I'd go that way.

 

[Dennis Alwon]

I agree 125 amps is the calculated value not 100 amps for the overcurrent protection. The feeder itself can be size ar 125% of the FLA one motor plus the Fla of the second motor.