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Old 09-24-2010, 02:36 AM   #1
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How many circuits can share a neutral?


Old house (remnants of knob&tube in the rafters) that, from the looks of the shiny insulation and breakers, was rewired recently. I'm not sure if the rewire was done by the same guy that did the garage wiring I described in another post (12g wire on a 30a breaker ), but from the spaghetti behind the breaker panel, I wouldn't be surprised.

Anyway, here's the question - from the breaker panel (surface-mounted on the outside of the house), there's a 3' length of 3/4 EMT that runs down to a weather-tite single-gang box at the the height of the crawl space. Through the back of this box, there are four or five NM-B cables (I can see a bit of the jacket on a couple) coming in from the crawl space. Going up to the panel there are a matching number of hots leading to as many breakers --- but only one neutral.

Is it okay to have this many circuits sharing a neutral? Or should every circuit have a dedicated neutral running all the way to the panel (except, of course, for 2-p breaker/shared neutral circuits, which is not the case here)?


Last edited by jeffeverde; 09-24-2010 at 02:39 AM.
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Old 09-24-2010, 04:12 AM   #2
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How many circuits can share a neutral?


No!It is not ok!

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Old 09-24-2010, 07:51 AM   #3
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How many circuits can share a neutral?


What size is the neutral? What size are the breakers? If the neutral is the same size as the other conductors then it is wrong.
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Old 09-24-2010, 09:46 AM   #4
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How many circuits can share a neutral?


Quote:
Originally Posted by jeffeverde View Post
Through the back of this box, there are four or five NM-B cables (I can see a bit of the jacket on a couple) coming in from the crawl space. Going up to the panel there are a matching number of hots leading to as many breakers --- but only one neutral.
What happens inside the single gang box? Is the jacket stripped away from all the NM cable and then the hots are run up the conduit and all the whites are wire-nutted together with a long pigtail going up the conduit to the neutral bar?
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Old 09-24-2010, 10:04 AM   #5
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How many circuits can share a neutral?


The NM-b is a code violation as they are located in a wet environment, conduit or not. And like the others said one neutral for multiple circuits is also a code violation. The exception would be a MWBC which it looks like you understand from your post.
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Old 09-25-2010, 03:37 AM   #6
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How many circuits can share a neutral?


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Originally Posted by a7ecorsair View Post
What happens inside the single gang box? Is the jacket stripped away from all the NM cable and then the hots are run up the conduit and all the whites are wire-nutted together with a long pigtail going up the conduit to the neutral bar?

-Yes, the neutrals pigtail together in the single-g box with a single conductor running up to the neutral bar

-No, the NM-B actually terminates in the box, and is nutted to THHN's that run from the box to the breakers (and the breakers are scattered on the panel and not pinned together as a MWBC's)

The neutral didn't look to be oversized, but I didn't dig beyond the first glance and thinking "this looks soooo wrong".

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Old 09-25-2010, 03:44 AM   #7
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How many circuits can share a neutral?


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The NM-b is a code violation as they are located in a wet environment...
Except where the conuctors enter this box (and then nut into THHN up to the panel), the NM-B is all inside the house in the under-floor crawl space. Does a crawl space count as a wet environment?
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Old 09-25-2010, 07:34 AM   #8
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How many circuits can share a neutral?


Quote:
Originally Posted by jeffeverde View Post
Except where the conuctors enter this box (and then nut into THHN up to the panel), the NM-B is all inside the house in the under-floor crawl space. Does a crawl space count as a wet environment?
No.
The only way to fix this is to run a white wire back to the for every hot wire you have.

This may include having to increase the size of the conduit and the size of the J box in the crawl space.
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Old 11-11-2010, 12:39 AM   #9
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How many circuits can share a neutral?


i have read on various electrician forums that it is OK for one A & one B phase circuit to share a neutral; since they are 180 out of phase they would cancel each other out. makes electrical sense to me.

i was thinking of doing this same thing... although i'm curious if GFCI's would work with this setup since they compare the hot/neutral current...
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Old 11-11-2010, 01:39 AM   #10
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How many circuits can share a neutral?


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i have read on various electrician forums that it is OK for one A & one B phase circuit to share a neutral; since they are 180 out of phase they would cancel each other out. makes electrical sense to me.
Yep that is common as long you pay attetion where you land it on the breaker and you will need legit two pole breaker not the twinners { espcally with GE breakers that will get ya if not carefull }

Quote:
i was thinking of doing this same thing... although i'm curious if GFCI's would work with this setup since they compare the hot/neutral current...
With two pole GFCI breaker it will work otherwise split it at the the junction box and run standard GFCI receptales { be prepared for price shocker on two pole GFCI breakers they are over 60 Euros.}

Merci.
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Old 11-13-2010, 08:17 PM   #11
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How many circuits can share a neutral?


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Originally Posted by frenchelectrican View Post
Yep that is common as long you pay attetion where you land it on the breaker and you will need legit two pole breaker not the twinners { espcally with GE breakers that will get ya if not carefull }



With two pole GFCI breaker it will work otherwise split it at the the junction box and run standard GFCI receptales { be prepared for price shocker on two pole GFCI breakers they are over 60 Euros.}

Merci.
Marc
ya, forgot to mention i was only talking about GFCI outlets. after thinking about it some more, i see it shouldn't be a problem since the outlet only senses the current diff. on the LOAD side.

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