Industrial Lighting

[Instrumentguru]

I am wondering if a common neutral can be used for more than one circuit, if the size of the neutral will hold the amperage of the shared circuits. IE: three 20 amp circuits using a common #6, and will this meet code? New to this site but I love the Q&A. Thanks

 

[charlie b]

What you are addressing is called a "multi-wire branch circuit," and it is allowed under NEC article 210.4. But there are restrictions that you need to understand, so I suggest reading it carefully. Also, if the three circuits originate from three different phases of a 3-phase panelboard, then the current in the neutral is likely to be far less than the current in any of the phases. Unless the lights are of a type that brings a lot of harmonics into play, you can use a #12 for the neutral.

 

[Pierre C Belarge]

Take a look at 310.15(B)(4), subsections (b)&(c).

 

[Instrumentguru]

Thanks for the quick reply and info. I was refering to 225.7 (B) in that one neutral for each phase. The question my colleges and myself have is if that one neutral could be shared if sized according to the ampacity of other circuits. I thank you guys for your answers, the code is sometimes hard for me to interpret.

 

[infinity]

Thanks for the quick reply and info. I was refering to 225.7 (B) in that one neutral for each phase. The question my colleges and myself have is if that one neutral could be shared if sized according to the ampacity of other circuits. I thank you guys for your answers, the code is sometimes hard for me to interpret.

That Article only applies to outside installations:

ARTICLE 225 Outside Branch Circuits and Feeders
225.1 Scope.
This article covers requirements for outside branch circuits and feeders run on or between buildings, structures, or poles on the premises; and electrical equipment and wiring for the supply of utilization equipment that is located on or attached to the outside of buildings, structures, or poles.

 

[Instrumentguru]

Yes Sir: these are outside lights on a ball mill.

 

[sinnadurai sripadmanaban]

common neutral

common neutral

If the current in the phase do not return via the neutral will the unbalance cause the RCD/GFCI to trip?