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Old 11-22-2011, 04:20 AM   #1
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electrical wiring-multiple circuits on one neutral


I'm currently working on a small restaurant that my client has purchased and is making renovations on before he opens. The panel has 29 circuits that are being used (four of them are 220). There are 11 neutral (white) and five ground wires coming back into the panel. My experience has been mostly with residential wiring using romax cable. So unless it's a three wire circuit (12/3 cable, usually to a kitchen) I always have one neutral and one equipment grounding conductor for every hot. I know this it the way it should be, whether using romex or wiring inside conduit. I have brought this to the owners attention, answering his questions as best I can. The problem is that my knowledge is quite limited, as I am a plumber. That is how I came to the job originally. After I finished, the owner asked if I could do some light wiring ( a couple of new outlets, a dedicated circuit for a new freezer, and a three-way switch). I took it on as I had nothing else to do for a few days. So what has to be done to make this a safe situation? That is what the owner whats. I told him I would find out. Does every circuit need to have a neutral? (I'm not that worried about the grounds, as it is all in conduit). I know what the code says, but in this situation, with no inspection and limited time and money, what do I tell tell my client? How safe, or maybe how dangerous, is his wiring.
And let me apologize to you licensed electricians for taking this on. I do a lot of things these days that I would pass on in better times.

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Old 11-22-2011, 05:57 AM   #2
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electrical wiring-multiple circuits on one neutral


Don't apologize to us, but there are MANY other safer things you could do to keep busy.

WOW! IMO you are crazy for doing this work in a commercial space with your limited knowledge. If you have to come here to ask basic questions such as this PLEASE reconsider telling him to hire a real electrician.
You can stick to wiring boilers and doing work in your own home.

Just for ethical and liability reasons there is NO WAY I am going to be a part of this. Sorry, I feel VERY strongly about this.

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Answers based on the 2008 & 2011 NEC.
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Old 11-22-2011, 06:31 AM   #3
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electrical wiring-multiple circuits on one neutral


In addition to Peteys comments if something happened because of an error you made he could lose his restaurant and you might end up in the deep stuff liability wise.

I understand your situation especially in tight times, but you need to look at the risk-benefit.
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Old 11-22-2011, 06:35 AM   #4
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electrical wiring-multiple circuits on one neutral


If you have 3 phase 120/208 volt power then three branch circuits, one off of each leg, can share one neutral. The neutral must be sized for the largest of the three. You mst use a triple wide triple breaker with at least 240 volt rating and with handles tied together.

For (regular) 120/240 volt power, two branch circuits, one off of each leg, can share a neutral, using a double wide double breaker in a manner similar to the preceding.

All permit and inspection laws need to be followed. In many cities you may not do your own electrical work in a building with more than one separately owned space (for example an apartment condominium), or in a building you are renting, or in a commercial building (store, restaurant, etc.).
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Old 11-22-2011, 05:44 PM   #5
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electrical wiring-multiple circuits on one neutral


If you "know what the code says" and you know what a multiwire branch circuit is and how it functions you should know the answer to your questions.
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Old 11-24-2011, 02:26 AM   #6
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electrical wiring-multiple circuits on one neutral


Your concerns are noted, guys. And thank you to AllanJ for helping me.
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Old 11-24-2011, 03:57 AM   #7
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electrical wiring-multiple circuits on one neutral


It is not possable to answer this question with out a lot more info,
Such as the types of loads, the current requirements of each,
The capacity of the neutral lines.
but suffice to say most electricains prefer all loads have there
own neutral line, this ensures maximum safety.
It really is a can of worms !
Dont touch it !
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Old 11-24-2011, 07:08 AM   #8
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electrical wiring-multiple circuits on one neutral


In the U.S. it is not permissible for two branch circuits fed by the same leg of the service to share a neutral even if the latter is oversized. However older buildings with this style of wiring are usually grandfathered until modifications are made to the affected branch circuits.
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Old 11-25-2011, 01:44 AM   #9
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Can of worms, no doubt. I've pretty much taken as far as I can and will recommend to the owner that he call in a licensed electrician for further work. I should mention that it is single phase 120-240 with a 200 amp service. Pretty much like the residential stuff I'm familiar with. As per AllanJ's posting, I believe that a few properly placed multiwire circuits could help restore some order to the panel. Am interested in how the selection of which circuits to put on it would occur.

Last edited by jimf1; 11-25-2011 at 01:55 AM.
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Old 11-25-2011, 07:50 AM   #10
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electrical wiring-multiple circuits on one neutral


Choosing which pairs circuits to designate as multiwire branch circuits usually depends on which direction (physically) they run.

At any point in the run a MWBC can enter a junction box and the red and white continue off in one direction and the black and white continue off in another direction. Beyond this point the portions of the circuits are treated as ordinary circuits.

This is often done where GFCI receptacles are installed. The load neutral beyond this point (for continuing GFCI protection to additional receptacles e.g. #3, #5, #7, etc) must be separate from the line neutral (continuing raw power to the next outlet box where, say, the other half of the MWBC gets GFCI protection). There the second and last GFCI receptacle can also protect receptacles e.g. #4, #6, #8, etc. with a separate load side neutral).

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