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I have some Z-wave light switches that I want to install; below is a link to the diagram for the light switches. Basically I can have all the wiring completed minus the neutral wire for the switch at the bottom of my steps. It will be harder for me to get the neutral from the light than run it in the basement. I have a junction box that is close (4ft compared to 100ft) but it's the living room circuit. Is there anything wrong with tying the light switch that needs the neutral to the living room neutral, based on the wiring is 12/2 and the breaker is the same amperage?

Proposed solution:
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  • Id like to add that the Hall lighting (Z-wave) is on the left side of the breaker and the Living room where I want to add the possible neutral is on the right side of the breaker – Brian Miller Feb 24 '13 at 8:51
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    No. See also: this question, and this question. If you're in the US, see National Electrical Code (NEC) 300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4). – Tester101 Feb 24 '13 at 13:25
  • Is there anything wrong with me running a 100ft wire to the breaker box and hooking up the neutral with the other neutral that is on the same circut? Basically having 2 exit points for the neutral? – Brian Miller Feb 25 '13 at 4:14
  • Yes, what is wrong is that it violates the NEC, as quoted by Tester101. Electrically, it is sound. But you are leaving an unused neutral wire just dangling there, since you found a more convenient return path. Neutral or not, a loose wire is a loose wire. – Kaz Feb 25 '13 at 6:18
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    @Tester101 your comment should be an answer. – The Evil Greebo Feb 25 '13 at 13:47
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The other answer and the comments are of course correct, but there is a second aspect to it: it won't work.

Actually, it may appear to work, until you try to install a GFCI just about anywhere on either of the two circuits involved.

A GFCI works by comparing the current through the hot wire and the corresponding neutral wire. If those two currents don't match, the GFCI will trip. When you "steal" the neutral from another circuit, the current will go out through one hot wire, but come back through a different neutral.

I actually had an older home where the dishwasher and some kitchen outlet were wired on two different circuits with a shared neutral (that was probably grandfathered in from an earlier era). Trying to bring the kitchen up to code, I was going crazy trying to figure out why the GFCI would trip every time I turned on the dishwasher!

  • Your answer is incorrect as a double pole GFCI doesn't require a neutral. – Kris Oct 12 '16 at 12:34
  • @Kris - true, but most GFCI that one would find in a DIY project aren't double pole. – Kevin Keane Oct 13 '16 at 21:12
  • Naaaa, it's talked about all the time. – Kris Oct 13 '16 at 22:57
  • Kevin check out a multi wire branch circuit, still allowed but they can have problems with gfci's. – Ed Beal Dec 6 '17 at 14:51
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No.

See also: this question, and this question.

If you're in the US, see National Electrical Code (NEC) 300.3(B).

National Electrical Code 2011

ARTICLE 300 Wiring Methods

300.3(B) Conductors of the Same Circuit. All conductors of the same circuit and, where used, the grounded conductor and all equipment grounding conductors and bonding conductors shall be contained within the same raceway, auxiliary gutter, cable tray, cablebus assembly, trench, cable, or cord, unless otherwise permitted in accordance with 300.3(B)(1) through (B)(4).

This other answer explains one reason why this code rule exists.

  • In short not following code will cause all current through that wire to generate RF interference. – Nelson Oct 11 '16 at 10:12
  • I agree for neutral but 2017 code allows for the ground to be separate so a ground can be added to 2 wire systems. – Ed Beal Dec 6 '17 at 14:48
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No, you can't steal a neutral wire from another circuit.

Each neutral wire is the return for the corresponding hot. If you "steal" a neutral from another circuit you run the risk of overloading that neutral wire (overheat, fire risk).

Another issue might arise if the circuit later becomes a GFCI. GFCI measures the current difference between a circuit's hot and neutral. Using another circuit's neutral will make the GFCI detect a current difference and it might trip.

  • Thanks for the advice. I will try to add more details. – albator Dec 6 '17 at 7:01

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