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I know just the basics of electricity and am trying to replace an older dimmer switch that broke with a new very similar switch.

The old switch is not connected to ground. The new switch has the green ground wire. I also see a couple of additional connections inside the junction box but can't tell what they are for.

I would appreciate help with (see pictures below): 1. Any idea what the other connections are for (black is for the switch, what are the white and copper colored ones for)? 2. Do I need to connect the ground wire to anything? If yes, to what?

Thanks!

Old connections: Old connections

New switch:

New switch

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    Instead of connecting the new switch to the existing pigtails, you can remove the pigtails and connect the wires from the switch using the existing wire nuts, to avoid an extra pair of connections. – prl May 5 '19 at 18:29
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    Please tag with your country!! AC wiring varies by country! – Clonkex May 6 '19 at 3:46
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The bare copper wires are the ground (grounds are either green or bare wires). You need to add the green wire from the dimmer to this bundle in the wirenut.

The white wires are probably the neutral, providing a return from the lamp to your electrical panel. If you had a smart switch that needed a neutral connection, you would connect there.

Note: this comments assume you are in North America. Different countries use different insulation color conventions. Thanks, @Clonkex, for the reminder.

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    Be careful!! In Australia, black would be neutral and, by process of elimination, white would be active! – Clonkex May 6 '19 at 3:48
  • @Clonkex Looking at the photos, it’s pretty clear that the OP is in North America. None the less, it is a good warning. – DoxyLover May 6 '19 at 7:02
  • Do the cap colours matter at all in the US? In the UK, using red for earth wires would be failed on inspection. – Andrew Leach May 6 '19 at 16:01
  • @AndrewLeach The color simply indicates the size of the wirenut and wire capacity, except for green nuts that are only allowed on ground and purple which are designed for connecting aluminum wires to copper. – DoxyLover May 6 '19 at 17:04
  • @DoxyLover I know you agree with me, but I just want to reiterate. Sure, it seems like the OP's native language is English, they use US spellings and the wiring looks like US wiring, but unless we're experts on wiring in every country around the world we cannot safely assume they're definitely in the US and give advice as such. When working with high-voltage electricity, assuming is a Very Bad Idea™. – Clonkex May 6 '19 at 22:48
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Any idea what the other connections are for?

In most household voltage alternating current (AC) circuits the white is the grounded neutral conductor; these are current carrying conductors (normally attached to a load along with the "hot/black" wire) and there is no reason for you to disturb them...

The bare copper conductors are most likely grounding conductors; you should attach the green wire on the new dimmer to these.

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    Be careful!! In Australia, black would be neutral and, by process of elimination, white would be active! – Clonkex May 6 '19 at 3:49
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    Nit: Neutral is not ground. It is supposed to be at the same potential as ground, but it must not be connected to ground – Carl Witthoft May 6 '19 at 12:11
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The bare copper wires with the orange wire nut are the ground. You should remove the orange wire nut and add the green wire to that connection. You may need a larger wire nut to handle three wires.

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This is obviously a North American installation. This is nms cable. Connect blk to blk and tie the green to the bare copper wiring. PLEASE determine circuit breaker and turn off power. Nuff said!

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