# Thread: Nails through plastic boxes - 314.23 (B)(1)

1. Junior Member
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## Nails through plastic boxes - 314.23 (B)(1)

Has anyone seen or heard of a situation where voltage has induced onto a nail that is driven through a box for means of support? It is allowed as long as the nails are within 1/4" of top/bottom or back of box.

My concern is that we have now introduced a piece of metal that is conductive and could create a hazard. We do this all the time in residential and I've never really thought about it until recently.

I would appreciate anyone's feedback.

2. I do it all the time and I don't see any issue with it.

This discussion has come up many times and we don't seem to get anywhere.

3. Welcome to the Forum!

OK. "Induced voltage" on a box support nail.

First, allow that the insulation on the current carrying conductors is intact and there is no conductor-to-nail electrical contact.

Second, induction happens in a changing magnetic field. In most normal wiring cases, the current into an electrical box is inside an insulated conductor and heads to a load. Having passed through the load, the current returns to the source inside an insulated conductor by going back to that same electrical box and on out the other side. That is, the current passing to the load through the electrical box is equal in magnitude to the current returning from the load through the electrical box, BUT, the return current is in the opposite direction and has an opposite magnetic field. The two magnetic fields cancel each other out. With no magnetic field, there is no induction on the nail.

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Originally Posted by al hildenbrand
Welcome to the Forum!

OK. "Induced voltage" on a box support nail.

First, allow that the insulation on the current carrying conductors is intact and there is no conductor-to-nail electrical contact.

Second, induction happens in a changing magnetic field. In most normal wiring cases, the current into an electrical box is inside an insulated conductor and heads to a load. Having passed through the load, the current returns to the source inside an insulated conductor by going back to that same electrical box and on out the other side. That is, the current passing to the load through the electrical box is equal in magnitude to the current returning from the load through the electrical box, BUT, the return current is in the opposite direction and has an opposite magnetic field. The two magnetic fields cancel each other out. With no magnetic field, there is no induction on the nail.
And even with induction on the nail, all that would happen is a difference in voltage between one end of the nail and the other, just like an ungrounded transformer secondary winding. No current would flow and without a fault to ground on one end the other end would not show anything but a phantom voltage to ground.

If you are using "induced" to refer to either inductive or capacitive coupling, then you have a simple phantom voltage of negligible current capacity.

If the nail is driven through the insulation of one or more wires, then you would have a problem!

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