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I am well aware that NEC allows the EMT conduit to be used as grounding conductor.

In my home, there is no dedicated grounding wire through the EMTs. I know this is fine.

When I recently got HP/HPWH installed, the electrician added a dedicated ground wire through the EMTs he newly installed (they go to another sub-panel, a junction box and the heat pump).

Is there any advantage of doing this? Is it considered "good practice"?

Is it worth pulling dedicated ground wires through my existing EMT conduits?

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  • 1
    Are those EMTs running atop a flat roof perchance? Nov 16, 2023 at 12:48
  • 1
    Belt and suspenders. And no need to economize, you paid for it. And as TPE alludes to, required where the EMT may be subject to abuse.
    – Ecnerwal
    Nov 16, 2023 at 14:02

3 Answers 3

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If the conduit might be damaged because it is run somewhere you might step on it for example then an explicit ground wire is required.

Otherwise the upside is that you then don't have to rely on the mechanical connection between the conduit and the electrical box at every point to be a sound electrical connection. This can be important in high current applications where ground fault along with a high resistance ground path can result in a fire rather than a breaker tripping.

The downside is that it fills up the conduit when it's not necessarily needed.

Pulling a additional ground through existing conduit with other wires already is going to be a chore and a half.

Instead if you find a loose conduit that doesn't make a sound electrical contact with the electrical box you can add a grounding clamp to the conduit where it enters the box and attach a ground wire to that to connect through.

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  • Could this be "insurance" on the contractor's part? If he ass.u.med the RMT was sound and relied on it, might he be liable if it turned out to be flakey?
    – TripeHound
    Nov 16, 2023 at 11:32
  • The requirement for this in the NEC comes from 440.9 (right now, it's only a requirement for rooftop HVAC units) Nov 17, 2023 at 3:23
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EMT for ground relies on

  1. Scratching the paint off, adequately, from breaker panels or other painted boxes to which it is attached,
  2. Set screws being tight, rust-free, etc.
  3. the system remaining intact over the long term,
  4. naive homeowners and handipersons not replacing it with PVC here and there,
  5. etc

For those reasons some electricians regard ground wires as more reliable. Others go by code and rely on the process by which code is written (X causes harm, stop doing X) to guide them. I think the smartest thing is to not get between these people. :)

Sometimes a ground wire will push conduit fill over the edge ... in those cases that should be the deciding factor, especially if the conduit is already in place. But again, some electricians would say this should be the trigger for bigger conduit.

As a DIY-er you might want to go with ground wires simply because paint-scratching is a bit of an art and there's no easy and reliable way to test it. Professionals know they are doing it right because they have practice. At least if one end of a conduit is in a painted box, you could run a wire there.

My guess is that in a house where the homeowner is aware of this question and thinking about it, the worries about EMT are already much less. You can mitigate the risks (if there really are any) a lot just by inspecting it.

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  • "Painted box". Is that a factory painted box for... (some purpose?), or a box that gets painted by careless painters who don't do a good job of masking?
    – FreeMan
    Nov 16, 2023 at 15:36
  • @freeman thanks, I clarified that in the answer, yes factory paint. Although "Etc" could include the effects of paint added to conduit later.
    – jay613
    Nov 16, 2023 at 15:53
  • Huh... you can get "decora" boxes to bury in a wall? What's the point... wonders aimlessly off into the distance? Oh, I guess "Handy boxes" are often surface mounted and I suppose getting one painted concrete color instead of zinc-plated steel would make it blend into the unfinished basement better... :)
    – FreeMan
    Nov 16, 2023 at 16:00
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    @FreeMan Code often requires life safety systems (fire alarms) have red conduit and boxes. Hospitals may also color critical power supplies green or orange. Black and white hardware is used for architectural purposes, think rooms with trendy open ceilings.
    – user71659
    Nov 16, 2023 at 21:18
  • Ah, good point, @user71659. Hadn't thought about that. However, unlikely to run across those when DIY around the house...
    – FreeMan
    Nov 16, 2023 at 21:39
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Does adding an explicit ground wire to EMT conduits provide any advantages? EMT conduit does not pass an absolute ground, since it's couplings are friction fit, so including a ground wire along with the other wires insures that whatever devices the EMT conduit feeds can be electrically grounded. A friction fit is subject to dirt, moisture and vibration all of which can destroy any possibility of grounding.

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