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I was replacing a standard light switch and noticed that the current light switch’s ground wire (green) was not being connected to anything. It was connected to the switch on one end and to a wirenut on the opposite end, however no other wires were included in the wirenut. The wirenut was simply terminating the single grounding wire.

This goes against my understanding of how a grounding wire should be wired, but this building is brand new construction and so must have passed inspection recently. Is this a valid way to ground a light switch and if so, why?

light switch

Machavity
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Brian P. Hamachek
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  • That does not work. The ground connection must go to your house ground. The wirenut in this case is only covering the end of the wire, it does nothing electrically. – JRE Nov 15 '17 at 12:48
  • That’s what I thought as well. I wonder how it passed inspection. Considering that the building in question is a 650+ occupancy high rise, it’s a little scary! –  Nov 15 '17 at 13:04
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    A picture or diagram would be helpful here. –  Nov 15 '17 at 13:04
  • @Finbarr I updated the post with a photo. The switch I photographed doesn’t even have a wirenut on the other end... –  Nov 15 '17 at 13:16
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    This is an electrical code question- better in the DIY SE- and will be specific geographically. The dimmer switch in question will be grounded to the metal box when installed via the mounting screws. If it was installed in a plastic box, connecting the earth wire would be necessary for safety. – Spehro Pefhany Nov 15 '17 at 13:26
  • @JRE Just a reminder, comments is not an appropriate place for answers, even partial. You should create an Answer to that affect. –  Nov 15 '17 at 13:40
  • You say standard light switch, but that is a dimmer and a pretty nice one at that. Just making sure you realize... – JPhi1618 Nov 15 '17 at 16:27
  • @SpehroPefhany Pretty sure that relying on the mounting screws to connect to a metal box is not acceptable in the UK! – Martin Bonner supports Monica Nov 15 '17 at 19:19
  • @MartinBonner I believe it was once acceptable and is no longer acceptable in the US-- see reference (and probably Canada as well), but older installations are grandfathered. I remember such switches with no ground connection at all. Since the triac is invariable heat sinked to the metal frame and there are screws that go through the cover plate, the triac-faceplate insulation there had better be extremely good. – Spehro Pefhany Nov 15 '17 at 19:52

3 Answers3

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The ground wire should be properly connected back to the box ground connection, or back to the line ground if there is no ground connection in the box.

Some will argue that the metal screws provide the grounding to the plate and so the ground wire is superfluous.

However, there are two issues with that.

  1. The screws and the screw holes are very loose tolerance. The screws wobble around in them. The plate itself gets painted over, OFTEN. Any paint or other contaminant, eg. drywall dust, can get into the screw threads and break that electrical contact quite easily. That leaves your plate ungrounded.

  2. When working on the switches, it is not uncommon to have them hanging out of the box while the electrician, or would be electrician / E.R. bait, works on the circuit as a whole. If you do not connect the ground wire, the plate again is, obviously, ungrounded.

The code in your area may indicate it is not necessary, so not doing so may be legally "valid", but for complete safety, you should wire it up anyway.

BTW: Inspectors do not inspect every outlet, that would take too long. Instead they normally sample test a few and trust that the electrician followed the same standards everywhere. The electrician, not knowing which outlets the inspector is going to test, is therefore "enticed" to do them all the same way.

Trevor_G
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    Usually what I see done, and do myself, is to loop the incoming ground to the box screw and leave enough length to pigtail to each of the devices in the box, to any outgoing grounds, and to each ganged box screw if it's an assembled gang and not a one-piece. Unless the electricians were dreadful and snipped the incoming ground to just a stub of an inch needed to get to the box screw there should be a ground wire in there to pigtail to. – J... Nov 15 '17 at 16:42
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    @J...more likely the sparky wired it up screwed it together, then noticed the green wire hanging there, capped it, and shoved it in knowing inspectors hardly ever check grounding on light switch screws. – Trevor_G Nov 15 '17 at 18:30
  • It is legal to use the yoke as a grounding method with a grounded metal box. The wire nut is there to prevent contact with a hot, I usually cut them off when using metal boxes. – Ed Beal Nov 15 '17 at 19:45
  • i don't see how paint could get on those screws. the cover screws yes, but not the box ones... – dandavis Nov 15 '17 at 22:08
  • I don't agree with the "abundance of caution" argument. Do it correctly, the end. @dandavis screw thread (or to be more precise, the yoke-to-screw-head interface) is not a legal grounding path. However if the box is not contaminated with paint, rust or goop, the screw-capturing little paper squares are removed, and the yoke bottoms out hard on the box - that is a ground path both acceptable and reliable. To say otherwise is to accuse you of not being able to do it right. – Harper - Reinstate Monica Nov 16 '17 at 00:47
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The wire nut was to prevent the bare wire from contacting anything charged within the box. Since the box itself appears metal, it's probable that the box itself is grounded. It's not great, but not dangerous.

The preferred way to handle grounding to the box is to use a grounding clip

enter image description here

Machavity
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  • As an example, your stock photo features a box not acceptable for yoke grounding. The drywall surface is proud of it, so the yoke will not be able to hard-bottom. – Harper - Reinstate Monica Nov 16 '17 at 00:50
  • "it's probable that the box itself is grounded" Code isn't exactly written with "probably" in mind. Either it is or it isn't grounded, and if it isn't you cannot do this. Find out which and then make your decision. – GManNickG Nov 16 '17 at 21:28
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The green ground wire of that dimmer is not required for the dimmer to operate correctly. It IS required to meet safety regulations and FCC noise radiation rules. However, it probably is redundant because the photo shows a metal wall box that probably already is grounded. In this case, the metallic connection between the dimmer mounting ears and the box provides the safety ground and RF shield connections.

The single ground wire was covered with a wire nut so it doesn't make accidental contact with anything live within the box.

AnalogKid
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