I just opened up the garbage disposal switch in my condo built in 1977 in the US. I believe this is the original switch, and therefore I will be replacing it right away with a new switch that has a ground screw. And of course, I will connect the grounding wire (see photo) to the ground screw. I consider it odd that the building has grounding wire, but that the switch has no ground screw. I have already replaced four light switches that had no ground screw in my condo.This is what begs the question.enter image description here

  • BTW: while the meat of the question's good, you're asking about UL 20 (the UL standard for typical wall switches), not the NEC itself... – ThreePhaseEel Mar 21 '18 at 1:22
  • OK, thanks. I was not aware of the “UL 20” standard before. But regardless of where the standard is found (be it the NEC or the UL), the question remains the same: in what year was all new construction in the US required to have light switches with ground screws (and also be grounded)? – MJCallinall Mar 21 '18 at 1:43

Technically it happened about the same time that UL started listing non-metallic boxes for residential use. When the boxes ("handy" boxes) were steel, any device body was grounded by virtue of the mounting screws. Once the boxes became non-conductive, the devices that REQUIRED grounding needed to have grounding screws. When I started as an electrician in the mid 70s, the code stated that for metallic boxes, you had to ground to the box but for non-metallic boxes (at that time they were still "bakelite"), you had to ground devices that "required grounding". That is still the way it reads to this day (250.148).

"One or more equipment grounding conductors brought into a nonmetallic outlet box shall be arranged such that a connection can be made to any fitting or device in that box requiring grounding."

The tricky part was, when did switches start "requiring" a grounding screw? That changed only when UL started requiring ground screws on switches, some time around 2010. When there was no ground screw, there was no "required" grounding.

  • The grounding screws are not (no longer?) a valid grounding path. For a metal yoke to ground to a metal box, the yoke must bottom out hard on the box (not held proud by drywall etc.), and there can't be rust, paint, schmootz or those little paper squares in the way. (paper squares holding the screw captive). – Harper Mar 21 '18 at 18:07
  • Thanx JR! Mystery PARTLY solved! All our boxes are plastic. Ergo, there is bare wire in the building so that a ground connection “CAN BE MADE” to any device that REQUIRED grounding. But if no ground screw, then no (legal) requirement for the light switch to be grounded. TRANSLATION: The NEC a/o UL caved to MBA lobby not to require light switches to have a ground screw, as connecting ground screws slows down constr. productivity! What still puzzles me is I have the 1975 NEC, and the “Guide to the 1975 NEC”. But neither has 250-148. BTW, I finished installing (incl grounding) the new switch. – MJCallinall Mar 21 '18 at 21:08
  • Thanks Harper! That may explain why they moved away from metal to plastic boxes. People with wet hands who touch the switch plate screws on garbage disposals can be electrocuted IF there is a short or GF in the appliance or switch, UNLESS, (1) the switch (w or wo ground screw) is properly grounded to the metal box(sans “proud drywall”/rust/paint/schmootz/paper squares), OR (2) the switch in a plastic box has a ground screw properly connected to the ground wire in the building. But for 41 yrs, NEITHER applied to my condo, ergo I put in a new switch w/connected ground, as I often had wet hands. – MJCallinall Mar 21 '18 at 21:52
  • Can one fit pigtail grounds to old switches by looping a pigtail around one yoke screw so that it contacts the yoke when the screw is tightened? – Jim Stewart Mar 22 '18 at 2:40
  • That’s a good question which ought to be submitted as an “original poster” (OP) question. I’m not an electrician. But I would think that even for an electrician, doing that would take so much skill and patience, that it would just simply be a lot easier to just buy a new switch (which are now required to have a ground screw) and use that instead. New switches are cheap to buy. Besides, I would rather doubt that that would meet code. But again, you need to repost this question as an OP question and get an answer from an electrician. – MJCallinall Mar 23 '18 at 6:10

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