Sharing a neutral

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Glenn Becnel

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A onsite electrical contractor states it is legal (per NEC) to share one grounded conductor (neutral) with (3) 120V circuits. My understanding has been, one hot - one neutral. This new installation is in a lunch room/break area for an industrial machine shop. The 120V circuits will be used for mirco waves, refrigerators, water coolers, coffee makers, etc.

Please give me a location in the NEC where this "legal installation" is found to be acceptacle.

Thanks in advance for your help.
 
Glenn Becnel said:
A onsite electrical contractor states it is legal (per NEC) to share one grounded conductor (neutral) with (3) 120V circuits. My understanding has been, one hot - one neutral. This new installation is in a lunch room/break area for an industrial machine shop. The 120V circuits will be used for mirco waves, refrigerators, water coolers, coffee makers, etc.

Please give me a location in the NEC where this "legal installation" is found to be acceptacle.

Thanks in advance for your help.
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It is called a multiwire branch circuit, you can find the definition in article 100.
 
It is a smart and efficient wiring method.

Roger
 
Those three circuits would need to be fed from a 208/120 volt Wye system.
 
Glenn Becnel said:
A onsite electrical contractor states it is legal (per NEC) to share one grounded conductor (neutral) with (3) 120V circuits.
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infinity said:
Those three circuits would need to be fed from a 208/120 volt Wye system.
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Correct. What you cannot do is have more than one hot from the same phase sharing a single neutral.
 
Isn't that allowance for festoon lighting, which I take to mean strung outdoor lighting like old used car lots and the old miniature golf places used?

Added: Even if I was convinced that a single full-sized neutral was permitted, I can't imagine ever, ever, ever coming up with a reason for doing so.

infinity said:
Isn't there a code proposal for the 2011 to end that debate once and for all? :)
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Oh, Lord, I hope so! :roll: (;))


Also added: Okay, inspectors among us: Who amonst you would pass such an installation, presuming proper raceway/cabling, sizing, and grouping requirements were met?
 
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LarryFine said:
Isn't that allowance for festoon lighting, which I take to mean strung outdoor lighting like old used car lots and the old miniature golf places used?
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Any outdoor lighting.

Added: Even if I was convinced that a single full-sized neutral was permitted, I can't imagine ever, ever, ever coming up with a reason for doing so.
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So you have never installed a service or a feeder?

A single neutral for many circuits. :grin:


Who amonst you would pass such an installation, presuming proper raceway/cabling, sizing, and grouping requirements were met?
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Better question, what code section would you use to fail it?
 
Oh boy, here we go again. :roll:

Ok guys, let me throw this real-world installation I ran into out for this discussion, and you all can tell me if it is Code-Compliant or not:

3 phase, 208y/120v panel
Total of five circuits, phased A,B,C,A,C All circuits 20 amp, 120 volt
A single (one) #10 neutral

What say the experts?

It was to an audio rack that had serious hum/noise issues and was constantly burning up amplifiers. All connections including the neutral were tight and no signs of heating, burning, arcing or other damage.

After we rewired to 5 dedicated neutrals, making NO other changes, the problems went away. Our solving of the longstanding issues won us a major bid to do a full upgrade on the client's screening room.

Let's leave the debate of why changing to dedicated neutrals solved the issues out of this, I am just curious as to if the installation was Code-Compliant to begin with.

And for the record, if this was say a lighting setup, otherwise working properly, and Code-Compliant I would not object to it or change it.
 
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iwire said:
Better question, what code section would you use to fail it?
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See post #11 above. Article 210.4 allows us to use MWBCs, and article 100 tells us what those are. Two hots from the same phase plus a shared neutral do not make a MWBC, and thus are not allowed.
 
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