More conduit questions


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Old 10-14-09, 07:28 PM
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More conduit questions

More conduit questions re my PVC conduit interor wiring project in my converted carport (now a detached garage/workshop), which has to be to code for the final inspection. I'm reading (Black and Decker Complete Guide to Wiring p 185) that "PVC conduit should be attached only to PVC boxes, never to metal boxes."

But I'm finding that while I can find rectangular PVC boxes and round boxes, and switch covers and two-hole outlet covers fo them, I can't find a GFCI cover (single rectangular opening) that fits them - the screw locations on the boxes are in the wrong positions for standard GFCI covers. I also can't find a PVC box that will attach to the inner side of my siding to which I can mount an exterior light fixture - the only model I can find has the mounting tabs at the bottom of the box.

These problems would be solved if I wasn't obsessing on everything being plastic. Will I be up to code if I use the painted metal boxes that have threaded conduit holes with my PVC conduit? Isn't that why they make the threaded PVC connectors?
 
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Old 10-14-09, 07:34 PM
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I see no reason that you may not use ANY metal boxes (4" square, Painted metal, etc) in your wiring. Another reason not to trust Black and Decker. You just need to make sure that you pull a ground wire, which you need to do with PVC anyway, and bond each metal box to the ground wire with a grounding screw or lead.
 
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Old 10-14-09, 07:44 PM
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Thanks for the fast reply. What is the purpose of attaching the ground wire to the ground screw on the metal box if the metal box itself isn't grounded (doesn't go to ground via metal conduit)? I'm not very knowledgable about this and am probably wrong, but I thought that was the purpose of the screw on metal boxes.
 
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Old 10-14-09, 08:46 PM
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What is the purpose of attaching the ground wire to the ground screw on the metal box if the metal box itself isn't grounded (doesn't go to ground via metal conduit)?
And what if the hot wire shorts to the box and it is ungrounded? You won't know till you touch the box. Then it's zaparoo time.
 
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Old 10-15-09, 07:12 PM
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Originally Posted by suobs View Post
Thanks for the fast reply. What is the purpose of attaching the ground wire to the ground screw on the metal box if the metal box itself isn't grounded (doesn't go to ground via metal conduit)?
By attaching the ground wire to the metal box, with the screw, you have, in effect, grounded it. Since you are using PVC for your raceway, it is required to pull a ground wire instead of using the raceway (which is not conductive) as your grounding means.

Originally Posted by suobs View Post
I'm not very knowledgable about this and am probably wrong, but I thought that was the purpose of the screw on metal boxes.
The only screw you may use for grounding purposes is one the is colored green and in a threaded hole which will be 10-32 thread in most cases. You may not use the 8-32 screws on the corners of the box or self taper/sheet metal screws.
 
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Old 10-15-09, 07:14 PM
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Gotcha - thanks. Metal box OK but pull a ground wire and connect it to green screw at each metal box.
 

Last edited by suobs; 10-15-09 at 07:32 PM.
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Old 10-15-09, 07:28 PM
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Unfortunately I have more questions.

Can I run wire from two circuits in the same conduit so they can both be controlled from a 2-gang switch in the same box?

And can the wires from one of the two circuits run back from the switch in the same conduit run that brought it to the switch?

If so do I need two ground wires in those sections of conduit?
 
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Old 10-15-09, 07:35 PM
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Originally Posted by suobs View Post
Unfortunately I have more questions.

Can I run wire from two circuits in the same conduit so they can both be controlled from a 2-gang switch in the same box?
Yep it done all the time

And can the wires from one of the two circuits run back from the switch in the same conduit run that brought it to the switch?
It depending on the numbers of conductors in the conduit size so you may get by ok with half inch conduit otherwise get 3/4 inch verison if you are running with #12's

If so do I need two ground wires in those sections of conduit?
Naw only one will do it due you will tie it all together.

However let me pass a quick tip when you have two circuits what I do is grab a small ziptie and wrap up one set of circuit and other circuits I use double ziptie so I know it on seperated circuit if not you can use electrical tape to group it.

Merci.

Marc
 
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Old 10-15-09, 08:03 PM
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Originally Posted by french277V View Post
It depending on the numbers of conductors in the conduit size so you may get by ok with half inch conduit otherwise get 3/4 inch verison if you are running with #12's
Just to add to Marc's post, unless you have more than 9 #12 wires in the conduit, you will be fine with 1/2" flex.
 
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Old 10-16-09, 05:47 AM
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Flex? It's schedule 40 PVC. I think I'll need in some cases 8 or 9 AWG 12 stranded wires. Will it fit in 1/2" PVC?
 
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Old 10-16-09, 06:43 AM
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Oops sorry. PVC. Your only allowed 8 #12 in 1/2" Sch 40 PVC.
 
 

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