Plastic boxes on concrete basement walls (?)

mdos · 08-25-2009, 03:17 PM

I'm running a couple of GFCI outlets in an unfinished basement. I'm using some tapcon screws to screw a 2x4 to the wall, and screw a plastic box to the 2x4, through the back of the box. The box is very stable, is this code compliant?

kbsparky · 08-25-2009, 03:39 PM

While this arrangement may work, it is a technical violation:

Quote:

314.43 Nonmetallic Boxes. Provisions for supports or other mounting means for nonmetallic boxes shall be outside of the box, or the box shall be constructed so as to prevent contact between the conductors in the box and the supporting screws.

adpanko · 08-25-2009, 04:25 PM

Yeah, you can't do that. Although it appears to work fine, the fastener has to be on outside of the box, such as the nails and guides that are attached to the tops and bottoms of most plastic boxes. You can't have the fasteners (in this case the heads of the screws you plan on using) potentially come in contact with the inner contents of the box (ie the wiring, outlet, switch, etc). Unlike metal boxes, plastic boxes aren't grounded, so if you get a hot wire coming loose and it were to touch the screw head, you'd have an ungrounded short.

**Termite** · 08-25-2009, 05:19 PM

Running the screws through the box or modifying the box in any way is a technical violation. This would be a good application for a metal box, since they have mounting holes in the back through which you can run screws.

mike242424 · 08-25-2009, 06:01 PM

i would do the same thing and just use a metal box

mdos · 08-25-2009, 08:36 PM

Thanks for the input, I'll pick up a metal box.

220/221 · 08-25-2009, 08:42 PM

Of course you can do this.

Quote:

Running the screws through the box or modifying the box in any way is a technical violation

Baloney. We "modify boxes in the feild on a daily basis by drilling and punching holes in them.

Quote:

i would do the same thing and just use a metal box

Plastic boxes are superior to metal because they are non conductive.

Quote:

314.43 Nonmetallic Boxes. Provisions for supports or other mounting means for nonmetallic boxes shall be outside of the box, or the box shall be constructed so as to prevent contact between the conductors in the box and the supporting screws.

The conductors aren't going to contact the screws in the back of the box unless you do something reall really stupid

Quote:

the fastener has to be on outside of the box

Somewhere, the NEC states within 1/4" from the back.

kbsparky · 08-25-2009, 09:52 PM

The OP didn't ask if he could do this or not, he asked if it was Code Compliant.

While many in the industry might engage in this practice, I maintain that it is not Code compliant, due to the section originally quoted.

The section you were referring to with the nails exposed on the inside of the box is 314.23(B)(1).

**Termite** · 08-25-2009, 11:27 PM

Quote:

Originally Posted by 220/221

Baloney. We "modify boxes in the feild on a daily basis by drilling and punching holes in them.

Can you cite an NEC reference that allows the modification of listed equipment by making holes where holes or knockouts weren't supplied? Since you called baloney I'm sure that you can find it.

There is a section requiring pass-through nails to be within 1/4" of the back of the box, but it doesn't say anything about making your own holes.

J. V. · 08-26-2009, 12:05 PM

Quote:

Originally Posted by mike242424

i would do the same thing and just use a metal box

Me too. Without the 2x4. Just mount it directly to the wall with Tapcons or nail drivers.
I would never use a plastic box exposed.

spark plug · 08-26-2009, 12:32 PM

To 220/221 (Poster #7) It's still a Technical violation. As stated by KB Sparky (#2)! But the NEC cites a specific reason; "That the conductors should not come in contact with the fasteners". True as you state. "Someone has to do something very stupid for the wires to come in contact with the mounting screws". But the NEC has to make provisions for all kinds of situations!(Now more than ever)

Don't Drink and Drive!!!

J. V. · 08-26-2009, 03:43 PM

Quote:

Originally Posted by thekctermite

Can you cite an NEC reference that allows the modification of listed equipment by making holes where holes or knockouts weren't supplied? Since you called baloney I'm sure that you can find it.

There is a section requiring pass-through nails to be within 1/4" of the back of the box, but it doesn't say anything about making your own holes.

Your post brings up something we were talking about on a pro forum a few weeks ago. Someone asked if anyone was using the mounting straps, the little metal tabs that allow you to mount the Bell boxes without having to punch or drill any holes in the box. I think like 99.9% said they do not use the tabs. I was the .1% who did use them. Most preferred to drill or punch the box.
Is it possible that the introduction of these mounting straps could be the result of the NEC requirement?

Stubbie · 08-26-2009, 04:27 PM

There is absolutely no reason to drill holes in a plastic box to mount it to anything. If your drilling holes in a plastic box then you are using it in the wrong application.

However in defense of what 220/221 says there wouldn't be a heck if a lot of difference than this box...which is code compliant. It is just "constructed that conductors cannot come in contact with the screws at least that is what they say...