Return to the Electrical Wiring Forum | Post a Follow-Up

 o
grounding old work plastic box to BX

Posted by homebound (My Page) on
Mon, Dec 7, 09 at 20:39

While swapping out a bathroom wall mount fixture, I see there's a plastic, round "old work" box that was used with the BX cable. Any advice on an easy way to ground the fixture without getting too involved with redoing everything? If I were to temporarily remove the box, I could reach the cable. Could I wrap/clamp some extra copper to the BX so I have something to connect with the fixture ground wire when the box is reinstalled? Thanks.


Follow-Up Postings:

 o
RE: grounding old work plastic box to BX

The term "BX" is sometime used a little loosely but I'm going to presume you have some kind of metal jacketed cable without a ground wire. For those kind of cables, the jacket is the equipment ground. With type AC cable there is also an aluminum bonding strap but that can't enter the box.

You need to either replace the box with a metal box or replace the cable with something with a "real" ground (NM-B [Romex] or metal clad cable, type MC).

I'm not sure an old work box is designed to support a fixture. Maybe someone could comment on that.


 o
RE: grounding old work plastic box to BX

Yes, I'm talking about the metal jacketed cable without a distinct ground wire. I was hoping to not replace the box, since the hole is round, I'd be patching drywall, etc. and the room just got painted. I was hoping to be able to attach a wire to the jacket and extend it into the box. No solution for that without swapping the box? BTW, the walls have metal and there is one adjacent to the box, for what it's worth.


 o
RE: grounding old work plastic box to BX

Plastic boxes are not listed for use with AC.

Without a cable clamp there is no way to obtain contact with the armor.


 o
RE: grounding old work plastic box to BX

I picked up a grounding wire clamp, size 3/8" to 1". Menat for pipe, of course, but think that will do it?


 o
RE: grounding old work plastic box to BX

There's no way that will meet code to accomplish what you want to do without replacing the box or cable. Plastic boxes are simply not approved for use with that kind of cable. Can you jury rig something? Of course, but it's not recommended.


 o
RE: grounding old work plastic box to BX

That might provide an electrical path to ground, but it won't be code-compliant. Please refer to Brickeyee's comment.


 o
RE: grounding old work plastic box to BX

Got it. Thanks much.


 o
RE: grounding old work plastic box to BX

If it were MC cable (with a ground in it) would the plascit box be ok? How would the cable be connected to the box?


 o
RE: grounding old work plastic box to BX

Fan box.

It's more than you need, but it will solve your problem.

Closest thing I can think of to what it is that you really need: a metal old-work box.

Here's an example


 o
RE: grounding old work plastic box to BX

"Fan box."

That would do the trick, and can be installed through the existing hole in the ceiling.

The clamps in the box are most likely for NM cable though, so you need to use a knockout with an AC cable clamp.

Hint: Attach the cable clamp to the cable and thread the wires through the knockout hole.
Place the box in the hole and pull the cable clamp into the hole and put the lock nut on and tighten.
Fasten the box to the bar.


 o Post a Follow-Up

Please Note: Only registered members are able to post messages to this forum.

    If you are a member, please log in.

    If you aren't yet a member, join now!


Return to the Electrical Wiring Forum

Information about Posting

  • You must be logged in to post a message. Once you are logged in, a posting window will appear at the bottom of the messages. If you are not a member, please register for an account.
  • Posting is a two-step process. Once you have composed your message, you will be taken to the preview page. You will then have a chance to review your post, make changes and upload photos.
  • After posting your message, you may need to refresh the forum page in order to see it.
  • Before posting copyrighted material, please read about Copyright and Fair Use.
  • We have a strict no-advertising policy!
  • If you would like to practice posting or uploading photos, please visit our Test forum.
  • If you need assistance, please Contact Us and we will be happy to help.


Learn more about in-text links on this page here