This picture is from a new building. It is not a 3-way light.

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there are three black wires coming out from the wall. One runs directly to the light switch. Two get connected in the blue connector, and then one runs to the switch.

I can see the white neutral at the back.

Where is the ground? And why are there three black wires?

I would like to replace this switch with a smart switch that requires neutral and ground connections.

1 Answer 1


I see two ground screws on the metal junction box, and grond wires being affixed to both of them. Since there are three MC cables entering the box, either those screws support 2 ground wires per screw, or there is an invisible wire nut.

  • So I should be okay connecting my MC cables from the smart switch in the same way they are currently connected with the existing switch, adding my neutral to others in the connector.. and connecting my ground to any of the copper wires screwed to the box?
    – ASH
    Jan 6, 2018 at 16:31
  • Why would they have three MC cables instead of two? (all three actually have a ground wire connected to the box at the back)
    – ASH
    Jan 6, 2018 at 16:31
  • @ASH "MC cable" refers to a specific type of multiconductor cabling used inside walls, Google it. You'll be using none of that today. The third cable is common, most likely it carries power onward to some other point of use. Attach your ground wire in the same fashion as the other ground wires are attached. If your ground wire is a different size, then go get 8" of ground wire that same size (if uncertain assume #12) and a wire nut, fit it normally, and pigtail it to your wire using a wire nut. Jan 6, 2018 at 16:54
  • This may not be MC. If it's old enough wiring it might be BX , which was outlawed because of its poor grounding abilities among a few other things. BX used to have a small integral aluminum ground in the metal wrap, and you pulled that ground back and squeezed it with the connector clip at the back of the box. You can ground the switch to the box with a grounding pigtail we commonly call a stringer. Jan 6, 2018 at 17:38

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