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I was just replacing a faceplate, and noticed that there was a large amount of unshielded copper wire twisted together in the back of the light switch electrical box. The light switch box is a larger box, containing a single and two three-way switches (3 switches in all). What is this wire in there for?

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You are probably looking at grounding wire, which is typically sheathed in green or is bare.

The bare wire serves as the equipment grounding conductor as a safety precaution. In the event of an electrical fault, the equipment ground will prevent you from becoming shocked and injured by coming in contact with bare metal in the box or on the metal casing of the switches or other receptacles (if there was an electrical fault).

It is perfectly normal and nothing to be alarmed about, it is a safety feature.

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And it makes sense for there to be a significant number of ground wires, as in a 3-gang box of switches, there are likely going to be a bunch of pigtails for the grounds to each switch, incoming line, and to each switched circuit. – MarkD Mar 18 at 3:32
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The ground wire is un-insulated. In metal electrical boxes, the ground wires should be connected to the green grounding screw in the back of the box so it is normal to see this.

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As well as the green grounding screw of the devices installed. – Skaperen Mar 17 at 12:28

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