I have 5 wires in the back of the light switch. It looks like there are 2 ground wires (copper, no coating) one from the breaker and one to the light. They go into different holes and then are coiled together.

The switch that I have now just has 2 wires going into it. No ground. The two copper wires are just twisted together and capped.

How can I install the new switch? Which one of the grounds do I use? And how is this light functioning now without a ground?

incomplete image of junction box

  • Is the new switch a dimmer or smart switch? It must support 3-way operation if it has 5 wires so a few might be unused. Or maybe you have 5 wires in the box? Not on the switch? Question is a little unclear. – JPhi1618 May 23 '19 at 18:41
  • New switch is just going to be a standard light switch. Not 3 way and not a smart switch. Is it possible not to use the ground (it is in a plastic box)? And why are there 2? – Brian May 23 '19 at 18:55
  • Which one of the grounds do you use? Did you happen to notice the bit where they are connected together? That isn't nothing...wires connected together are not spares for you to use one of, they have an important job already, and splitting them will break that... – Harper - Reinstate Monica May 23 '19 at 21:11

Based on your wiring color and photo, I'm going to assume this is an older house in the US.

First a few things. Sometimes there are wires in a box that just pass through and go somewhere else, so all the wires might not be used by the switches or outlets in a given box. It's not unusual to have 5 wires in a switch box.

Also, the ground wire is there for safety. Lights and appliances don't really "use" the ground, and ideally it should never carry any current. All ground wires in boxes and fixtures just get connected to each other like a safety net that catches and stray electricity and makes sure it gets back to the main breaker box (to hopefully trip a breaker in a dangerous situation). Older wiring practices didn't always use the ground, but now almost everything is connected to ground including light switches.

So, for the new switch, hook up the same two wires that go to the old switch and then you will need to "pigtail" the ground and connect it as well. A pigtail is a short wire that runs from a bundle of wires and connects to a device. So, it's not a matter of "which" ground wire - it's both.

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I count 6 wires in the box - I have circled the extra black which immediately diverts out of frame.

enter image description here

Anyway, this connects like a normal switch:

  • Pigtail a ground to the switch then all grounds together under the same wirenut
  • If the switch needs a neutral, pigtail it, then all neutrals together
  • Each of the two remaining black wires to the switch
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