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I'm rewiring my house, and keeping some circa 1920 light switches, which don't have ground screws. The switch cases are porcelain, and have a brass yoke. I originally planned to sandwich a ground pigtail between the yoke and the box, but since the metal box itself is grounded, I figure the yoke will already be grounded to the box via the mounting screw. Is it necessary to pigtail a ground wire directly to the yoke, or would they just add clutter to the box?

push button switches, front and back

push button switches, yoke angle

zwiebelspaetzle
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1 Answers1

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I would not worry about adding a “wire” to the switch either the box grounded those nice bright brass yokes being connected to the metal box will be more than enough grounding (in the US it is code compliant to use this same method with some devices). Your switches look to be in exceptional condition I hope the contacts are also if so they may last another 100 years.

JACK
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Ed Beal
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    So glad th OP's saving those switched.+ – JACK Jul 06 '20 at 20:24
  • Thanks! It took a bit of effort to get them clean :) – zwiebelspaetzle Jul 06 '20 at 20:42
  • Looks like the backs can be removed to service the switch. – Jim Stewart Jul 06 '20 at 21:32
  • I have read on this site that the screw threads-to-box paths are not rated for high current. For a good ground the metal tabs on the switch are supposed to make hard conducting contact with the metal box. Make sure there is no air gap or other interference with conduction. If a box is set too far in, use metal shim spacers to get the switch in the plane of the finished wall surface. – Jim Stewart Jul 06 '20 at 21:51
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    @jim Stewart this site is not always correct , consult the NEC, as my answer said the metal yoke in contact with the box , the 32 pitch screw normally self forming not self tapping is enough contact as defined by code. the yoke is over 100x that plus the screws – Ed Beal Jul 06 '20 at 22:39
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    Yoke-to-box is fine for switches, just not for receptacles (unless they're the self-grounding type, or have direct metal-to-metal contact with surface mounted metal boxes) – ThreePhaseEel Jul 06 '20 at 23:23
  • (FYI: the Code ref for grounding switches is 404.9(B)) – ThreePhaseEel Jul 06 '20 at 23:29