multiple motors single feed

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JeffD

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Location
cleveland, oh
I have been reviewing Mike Holt's NEC Exam Prep book and in the motor section it is covering when you have multiple motors on one feed. They share short circuit/ground fault protection and have their own overload protection. I assume the motors will be tapped off of a wireway. I come from a heavier commercial / institutional background and never see this design in practice. My question is how common is this and in what situations do you see this used?
 

augie47

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Location
Tennessee
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State Electrical Inspector (Retired)
unless I am overlooking some use, it seems to be seldom.
In order to share short-circuit ground fault protection that protection must cover all motors.
The few times I have seen that is on small motors taking advantage of thre samllest standard breaker being 15 amp.
Sharing a feeder to a group of motors, each with it's own SC/GF and OL protection is commonplace.
 

RonPecinaJr

Senior Member
Location
Rahway, NJ
I haven't seen many motors wired like this from a tap but it seems like a good way to charge a lot without spending a lot.

Feeder size - 430.24

Feeder OCPD for this kind of set up - 430.62(A)
 

JeffD

Member
Location
cleveland, oh
And just to make sure I have this right wouldn't you use the same procedure to size the breaker feeding an mcc. Take the largest rated motor's FLC time table 430.52 and then add the flc of the other motors. And the feeder would be taking 1.25 times the largest rated motor's flc and adding the others for the minimum feeder size or am I missing something?
 
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