2 & 1hp motors on one circuit

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tryinghard

tryinghard

Senior Member
Location
California
Scenario:
1 3ph 2hp 240v motor = 6.8, includes starter
1 3ph 1hp 240v motor = 4.2, includes starter

Would like to have these on one circuit, wouldn?t this arrangement be considered a feeder rather than a branch due to the OL?s?

If so 430.62(A) applies rather than 430.53 and OCP sizing would be:
17 = 6.8 x 2.50 for the 2hp
4.2 = 1hp (4.2 x 2.5 = 10.5)
21.2 = OCP
Therefore the maximum acceptable, inverse time, breaker size would be 15A in light of 430.62(A), 20A is too large.

Is this correct, any other thoughts?
 
tryinghard said:
Scenario:
1 3ph 2hp 240v motor = 6.8, includes starter
1 3ph 1hp 240v motor = 4.2, includes starter

Would like to have these on one circuit, wouldn?t this arrangement be considered a feeder rather than a branch due to the OL?s?

If so 430.62(A) applies rather than 430.53 and OCP sizing would be:
17 = 6.8 x 2.50 for the 2hp
4.2 = 1hp (4.2 x 2.5 = 10.5)
21.2 = OCP
Therefore the maximum acceptable, inverse time, breaker size would be 15A in light of 430.62(A), 20A is too large.

Is this correct, any other thoughts?
Click to expand...

I'm assuming your talking about having a feeder circuit feed two starters which in turn then feed each motor. In this case you need to size the feeder as follows:

2 HP = 6.8A
1HP = 4.2A
25% largest motor = 6.8*.25= 1.7A
Total = 12.7A

I would therefore use a #10 (smallest allowed) and have a 30A OCPD.

I believe this is correct.
 
I would not consider an OL as an ocp.

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.

What you have, I believe is a branch circuit feeding two motors.
 
tryinghard said:
Scenario:
1 3ph 2hp 240v motor = 6.8, includes starter
1 3ph 1hp 240v motor = 4.2, includes starter

Would like to have these on one circuit, wouldn’t this arrangement be considered a feeder rather than a branch due to the OL’s?

If so 430.62(A) applies rather than 430.53 and OCP sizing would be:
17 = 6.8 x 2.50 for the 2hp
4.2 = 1hp (4.2 x 2.5 = 10.5)
21.2 = OCP
Therefore the maximum acceptable, inverse time, breaker size would be 15A in light of 430.62(A), 20A is too large.

Is this correct, any other thoughts?
Click to expand...

If your starters don't have short-circuit/g fault protection then, as Dennis says, this is a branch circuit and I agree with you on the 15 amp max.
In the real world, I might question the 15 amp breaker handling the two motors.
 
augie47 said:
If your starters don't have short-circuit/g fault protection then, as Dennis says, this is a branch circuit and I agree with you on the 15 amp max.
In the real world, I might question the 15 amp breaker handling the two motors.
Click to expand...

Okay I think I agree that this scenario could be a branch circuit rather than a feeder. I say ?I think? because the OL of the starter for a motor is the branch circuit protection it?s just not clearly ?the device? (notice 430.31 and feeder?s definition).

Anyway not much difference in this case, so 430.53(B) applies to size the overcurrent protection device (inverse time breaker):

17 = 6.8 x 2.50 for the 2hp
4.2 = 1hp (4.2 x 2.5 = 10.5)
21.2 = OCP
Therefore the maximum acceptable breaker size would be 15A in light of 430.53(B) because of the 1hp motor, 430.53(D)(1) applies as well.

Gus, I don?t think its extreme risk to use a 15A because it would still be 221% instead of 250%. But I wonder if an overcurrent situation occurs during start up (or simultaneous start up) if 430.52 Exc #2(c) could apply allowing an upsize to 20A?
 
mull982 said:
I'm assuming your talking about having a feeder circuit feed two starters which in turn then feed each motor. In this case you need to size the feeder as follows:

2 HP = 6.8A
1HP = 4.2A
25% largest motor = 6.8*.25= 1.7A
Total = 12.7A

I would therefore use a #10 (smallest allowed) and have a 30A OCPD.

I believe this is correct.
Click to expand...

I think my scenario requires the breaker sizing first to accommodate start up (LRA); otherwise the breaker could be too large for the smallest motor and violate 430.53(B).

Once the breaker size is determined the conductors can be sized according to the breaker.
 
Cow said:
6.8 x 250%=17(round up)20 amp brkr

20 + 4.2A=24.2 amps(round down)20 amp feeder brkr.
Click to expand...

Or (6.8 x 250%) + 4.2 = 21.2, round down 20A :cool:

But this may not fit well with 430.53(B) ?where it can be determined that the branch-circuit short-circuit and ground-fault protective device will not open under the most severe normal conditions of service that might be encountered.? Severe, normal, & might, are almost oxymoron?s ? I suppose one should simply avoid this.
 
tryinghard said:
Okay I think I agree that this scenario could be a branch circuit rather than a feeder. I say “I think” because the OL of the starter for a motor is the branch circuit protection it’s just not clearly ”the device” (notice 430.31 and feeder’s definition).

Anyway not much difference in this case, so 430.53(B) applies to size the overcurrent protection device (inverse time breaker):
Click to expand...
actually 430.53 applies to the motor branch circuit short circuit and ground fault protection device, hence why the overload protecton isn't relative here
tryinghard said:
17 = 6.8 x 2.50 for the 2hp
4.2 = 1hp (4.2 x 2.5 = 10.5)
21.2 = OCP
Therefore the maximum acceptable breaker size would be 15A in light of 430.53(B) because of the 1hp motor, 430.53(D)(1) applies as well.

Gus, I don’t think its extreme risk to use a 15A because it would still be 221% instead of 250%. But I wonder if an overcurrent situation occurs during start up (or simultaneous start up if 430.52 Exc #2(c) could apply allowing an upsize to 20A?
Click to expand...
This exception says "motor" IMHO don't think we could apply it to motors
 
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