Wiring – How should I attach the grounding conductor for a replacement switch

dimmer-switchlightingswitchwiring

I'm attempting to replace an old Leviton light switch with a new Lutron dimmer switch that connects to our house's Wink system. The old switch had 3 black wires attached to the light switch and no ground wire.

Old switch:
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New switch:
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Other reference picture:
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Upon further investigation, the box appears to be grounded itself. There is a bare copper wire screwed to the back of the box.

Pictures:
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Since it appears the old switch was grounded via the box, can I just ignore the grounding wire on the new switch and let it work the same way?

All the pics are hosted in an album here for easy viewing as well.

Best Answer

You would be best advised to shut off all live power feed to this box. Then pull the existing bare copper GND wires out of the back of the box and add an additional bare copper wire pigtail to the bunch. Then reattach to the box with the proper green grounding screw.

The new pigtail will get wire nutted to the green wire on your new dimmer switch using an appropriate green twist on wire nut.

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