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Old 05-25-2011, 07:56 PM   #1
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3-way switch loop with thhn


So another question comes up as I plan my run for my 3-way switch in the house to operate a light in my detatched garage. The THHN will have to be in conduit from one end to the other, and will go into metal boxes on each end. I already know that bonding the metal boxes is something my inspector is going to be looking for...

So does that mean that I need to pull a ground conductor with the THHN, so I would probably ideally want to pull 2 black runs, 1 red run and a green run and use the green to pigtail so I can bond the metal junction box on each end and ground the switch?

Now that I talked it through it seems to make complete sense, but I'd appreciate confirmation that I have it right since I'm learning that wirint with individual conductors is a little different than the romex wiring I've mostly dealt with.

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Old 05-25-2011, 09:09 PM   #2
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3-way switch loop with thhn


A ground conductor is only required when installed in non-metallic conduit.

It's entirely optional with a metallic conduit system.

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Old 05-25-2011, 10:08 PM   #3
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3-way switch loop with thhn


When you use romex wire the ground wire is supplied within the cable. When you use individual wires as you are planning, the metal conduit supplies the ground. Of course if you use PVC conduit you would need a ground wire.
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Old 05-25-2011, 10:34 PM   #4
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3-way switch loop with thhn


I'm half way tempted to put the green wire in anyway just to be sure that he doesn't decide to interject his judgement that EMT conduit connections are unreliable connections for ground continuity. Good to know though that if I wanted to save the $12 for another 50' spool of green THHN that it wouldn't be a code violation, but if $12 can reduce the risk of him making me take another half day off work, I might take the extra precaution.

So let me point out again that my inspector seems to tend to take the most strict interpretation approach and go beyond. Requiring bracing based on the weatherhead height? There's no load at the weatherhead. Rejecting schedule 40 PVC conduit citing physical damage where it is surface mounted behind a utility sink that is bolted to the concrete floor?

Is there any tendency among the skepticle to have doubts about the reliability of ground continuity through set screw connections in EMT conduit? Or am I being too paranoid?
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Old 05-26-2011, 03:51 PM   #5
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3-way switch loop with thhn


Based on what you are saying about the inspector, go ahead and run the wire. Unfortunately the inspectors interpretation of the code will have the last word
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