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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: enter image description here

New switch: enter image description here

Other reference picture: enter image description here

Upon further investigation, the box appears to be grounded itself. There is a bare copper wire screwed to the back of the box.

Pictures: enter image description here enter image description here

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.

  • Can you specify how the three black wires were attached to the switch? Hopefully there were not two of the black wires under one screw. From the looks of this box configuration power arrives at this box on an incoming wire set. The switch either turned power on/off to one or two exit wire sets from the box. If there is only one switched exit wire set then the other exit set is passing through a live power feed from this box to some other location. – Michael Karas Jan 24 '15 at 21:06
  • @MichaelKaras your second assumption appears to be correct. I think live power was running through to something else. I think a GFCI outlet in the bathroom. This entire light appears to be wired into the GFCI breaker. I shut off all power in the house while working on it. The new switch appears to be working without the ground. – Kyle Jan 24 '15 at 21:35
  • The functioning of the dimmer switch does not depend on the green grounding wire. By not hooking up the green grounding wire you have potentially compromised safety in the case the switch ever develops an internal fault. To be honest the manufacturer provides the green wire because depending on the screw through the frame of the switch can be unreliable. Also since a dimmer with electronic components inside is more prone to failure than a regular mechanical switch it gives even extra weight to the argument that you should be connecting up the green wire rather than ignoring it. – Michael Karas Jan 24 '15 at 21:42
  • Thanks for the tip, I'll get it pulled out completely and wire a ground leg into it. Appreciate it! – Kyle Jan 24 '15 at 21:56
  • You DO NOT need to attach the green tail to the grounding wire in the box. By properly attaching this device to a properly grounded metallic box you are inherently providing an adequate grounding path. – Speedy Petey Jan 25 '15 at 2:32
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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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You do not need to attach the green tail to the grounding wire in the box. By properly attaching this device to a properly grounded metallic box you are inherently providing an adequate grounding path.

NEC 2011

404.9 Provisions for General-Use Snap Switches

(B) Grounding.

Snap switches, including dimmer and similar control switches, shall be connected to an equipment grounding conductor and shall provide a means to connect metal faceplates to the equipment grounding conductor, whether or not a metal faceplate is installed. Snap switches shall be considered to be part of an effective ground-fault current path if either of the following conditions is met:

(1) The switch is mounted with metal screws to a metal box or metal cover that is connected to an equipment grounding conductor or to a nonmetallic box with integral means for connecting to an equipment grounding conductor.

(2) An equipment grounding conductor or equipment bonding jumper is connected to an equipment grounding termination of the snap switch.

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