What would be the proper way to ground this new Legrand Starter Box (BW5) if the ground cable inside the previous box and it's too short to reach the new box or receptacle?

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The original cabinet makers misjudged how high the cabinet would be and made a box opening right at the bottom of the shelf and never placed a wall plate there. I decided to install a metal Wall Box instead on top. Since the 2 metal boxes are not touching, no ground. Whoops!

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  1. What options do I have here to ground the new wall box with the old grounding cable?
  2. Can I simply cut my own ground copper cable and connect it the old box to the new with a new screw?
  3. Can/Should I use a waco connector?
  4. Would that be an acceptable way of extending the old cable to the new box or receptacle?
  5. Do it matter if I connect the new ground cable to the Legrand box or the receptacle?
  • 1
    Is that box grounded via metal conduit...? It sure looks like there's conduit coming into it... May 16, 2022 at 4:01
  • Are you talking about the original box that's inside of the drywall? From what I understand, all the electrical that ran through our house was metal conduit. But this specific drywall metal box might have been installed 10 years ago or when the house was built. I'm not sure. Does it actually matter how the internal box was grounded? Would that alter the answer? All I know is, my receptacle is showing open ground. And it's obviously due to the fact that the new box is not ground. There is no connection between the original metal box and the new metal wall box. They are separated by wood. May 16, 2022 at 4:13
  • It matters how the original box was grounded, because it means that that "ground wire" may not even need to reach into the new box at all -- you'll need to use a pigtail or ground jumper to bond the old box to the new box in that case May 16, 2022 at 4:17
  • Okay, I was also wondering if that was going to be possible. So just use a pigtail to the original box and connect it to the receptacle, then retest. And if it gives me a "correct wiring" display. I'm good to go, right? May 16, 2022 at 4:27
  • 1
    The 3rd ground to the device isn't necessary if the device is "self grounding".
    – FreeMan
    May 16, 2022 at 12:09

1 Answer 1


Your wiring is in conduit (as evidenced by the blue wire which isn't a standard cable color).

  • IF your conduit is properly grounded (as it should be), your metal box will already be grounded. Simply bond the two boxes by running a jumper from one of the 10-32 holes in the deeper box to one of the 10-32 holes in the new box and it will be properly grounded.

  • If the conduit is not acting as ground (as potentially indicated by the green wire), you still only need to bond the two boxes as in the point above.

    • Note that the green wire could go down a run that's partially metal and partially plastic conduit, or feeds into a plastic box. This would likely mean that your metal conduit is the ground, but that this one run is going somewhere where there isn't a complete metal conduit feed so the ground wire is necessary.

The device itself shouldn't need a ground to it. It should be self-grounding if you remove the paper square that holds the mounting screws in place but also insulates the device from the box. Removing that paper square ensures a good grounding connection to the box.

  • If I ground only the receptacle, does that mean the box also gets grounded? Like when you ground only a receptacle, does the entire unit get grounded? or only specific parts in the receptacle? Or does it depend on the receptacle? May 17, 2022 at 20:54
  • @OutdatedComputerTech -- the box in the wall is already grounded. the extension box needs a ground pigtail. the receptacle should be able to pick up ground from a surface-mount extension thru hard-flush metal-on-metal contact. May 17, 2022 at 22:57
  • @threephaseeel - I'm only talking about the exterior box. The two of you are saying to ground the Legrand box from the conduit box, which will also ground the outlet. I get that. But what about grounding the receptacle. Does that also ground the Legrand box as well? Or does that depend on the type of outlet? May 17, 2022 at 23:29
  • @OutdatedComputerTech -- does the starter box not provide a place to land a grounding screw on it? May 18, 2022 at 2:47
  • 1
    I would imagine so, @OutdatedComputerTech. However, code requires that the box be grounded and transfer to the device so that if the device is removed the box doesn't become ungrounded. In your scenario, the Legrand box would be ungrounded as soon as you remove the device from it. A minor, subtle difference that may or may not matter in practice, but is a code violation
    – FreeMan
    May 18, 2022 at 10:57

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