07:18PM | 03/10/01
Member Since: 04/17/00
10 lifetime posts
I am installing 5 dimmer switches in a 5-gang box. Under the NEC, do I pigtail all 6 12-gauge wires in one pigtail? If so, I will have to find a very large wire nut. Or is there some other way to connect so many wires? Or should I make 2 or 3 pigtails and connect them?


03:48AM | 03/12/01
Member Since: 01/18/99
47 lifetime posts
This came from another forum. Wg is an electrical inspector, author of a number of textbooks on interpetation of the NEC and teacher of same.

The number of conductors allowed in the box that is stamped inside the box refers to the total capactity of that box to contain that number of current carrying conductors. However that stamped number in that box does not allow for any reductions for devices, equipment grounding conductors, straps, hickeys, etc. that also must be counted as current carrying conductors.

NEC 370-16-b states approximately the following, more is said in that article but this is the basics.

14 Ga wires must be provided 2 cubic inch of box capacity for each current carrying conductor in that box. 2.25 cubic inch is required for 12 ga wire.

It goes further to say that you must deduct one current carrying conductor for all the bare or green wires in that box as a total of one conductor reduction to you capacity of that box.

A device must deduct 2 current carrying conductors for each yoke [mounting bracket of each recepacle, switch, etc.

A strap or clamp that enters the box 1/2" must also deduct 1 current carrying conductor for a total of all straps in that box counted as one deduction.

A pigtail that originates within that box but does not leave that box is not counted as a current carrying conductor.

Any wire that enters or leaves that box whether wire nutted together or not must be counted as one conductor for each entry or exit with the exception of the rule for green or bare wires.

Any wire that passes through that box but is not cut in that box is only counted as one.

A few other rules apply and are in 370-16 but those are the main rules of this subject.

The above calculation method applies to any conductors 14 ga through 6 ga.

Any box containing #4 or larger conductors must be counted by a different method due to there size.

Hope this helps



04:03AM | 03/12/01
Member Since: 03/13/00
1675 lifetime posts
Now that you know how to measure the box...
I would "make 2 or 3 pigtails and connect them" as you suggested.
One more thing... If you have nothing else on that circuit, you shouldn't need 12 guage wire - 14 would do, and it's much easier to work with.

[This message has been edited by rpxlpx (edited March 13, 2001).]


06:06PM | 03/14/01
Member Since: 07/21/00
76 lifetime posts
I agree with Rpxlpx, Do not put too many wires together even with a large wire nut, even though you might find a large one(usually blue or grey). A bad joint is more dangerous than several joints. Wire nuts also have a capacity rating which should be followed, check the box for their capacity. Yellows will hold 3 #12, reds 5 #12. As for how many Joints can be made, It can get difficult to determine this as you can see by the code quoted by Bink. Just be sure not to "cram" everything into the box, try to leave ample space to install the devices. Remember that dimmers require more space than switches. Try to fold the wires back into the box in a neat manner and make sure everything fits without force. Good Luck, Bill.
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