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I replaced a light switch installed at the bottom of the basement steps with one that has a dimmer. When I opened the junction box i saw there are two Romex wires coming in. One is connected to the switch at the top of the stairs which makes sense as this is a three way switch. I don’t know what the other one is connected to. The copper is connected to the ground, but the black and white wires are exposed and not connected to anything. Is this some kind of standard practice I’m not aware of or should I disconnect the ground and cap off the wire? I’m assuming the mystery wire is not live. I’m picking up a voltage meter tomorrow to confirm. Even if it’s not live, I feel uneasy having exposed random wires in the box. Any advice or input would be greatly appreciated.

  • Examine the place where power is delivered to this lighting circuit, ie. at the other switch or at the lamp. I'll bet the circuit is not properly grounded there because no reliable fault ground is available. – A. I. Breveleri Sep 8 '18 at 3:04
  • Thanks for the feedback. The other box is grounded. – ATGoldy Sep 8 '18 at 15:01
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It's not unusual to see an unused wires folded up in a box with the ground connected and the other conductors capped. Unfortunately it's very rare to see anything marked or labelled to help the next guy figure out what's what.

This one's a little different in that it's clipped short on purpose - someone wanted to discourage trying to use the wire - and the wires are not capped.

I'd cap the wires and leave it alone. Turn off the breaker for the light circuit, test to see if the short wire is live, and if so find and turn off that breaker. I'd peel back the jacket 1/2", carefully strip 1/4" or so off the black and white, and twist on a small wire nut.

Tracing the wire to figure out where it goes and the rest of the story could be a bit of a project, and there's nothing to indicate any hazard, so I would not bother.

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    Great input. Thank you so much. I am going to try exactly what you suggested. Will update with findings. – ATGoldy Sep 8 '18 at 15:02
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    I tested the mystery wire and as expected it is not live. I guess the electrician used it to ground the box. I capped the wires and closed up the box. Glad to have that concern off my mind. Thanks to all who helped. – ATGoldy Sep 9 '18 at 4:36
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It looks like someone retrofitted ground and used a whole Romex to do it, possibly to avoid rules in the Electrical Code that restricted retrofitting ground. In 2014 Code those rules were abolished and it's now legal to run just a ground wire.

  • Yeah... I was the thinking the same. Thanks for the input. – ATGoldy Sep 8 '18 at 18:46

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