Plastic NM clamp in a metal box?

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Old 01-07-11, 04:33 PM
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Arrow Plastic NM clamp in a metal box?

Hi,

I have metal boxes in my house and am keeping any new boxes I add metal too, for simplicity. I've always used the traditional 2 screw metal NM cable clamps that tighten into the box knock-out when securing Romex (NM).

I came across some plastic snap-in NM clamps that looked interesting and less of a hassle to use. I've never seen them before so I want to be sure that they do get used in metal boxes - the package says nothing. Also, anyone heard of inspectors having issues w/them? Is there any downside?

Thanks guys.
 
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Old 01-07-11, 04:37 PM
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What you're describing is perfectly legal and safe. Just an FYI, when using metal boxes, the box must be bonded. Actually, that's what those connectors are designed for.
 
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Old 01-07-11, 04:49 PM
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Isn't tying a ground pig tail to the grounding screw bonding the box?
 
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Old 01-07-11, 05:23 PM
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Yes, you pigtail the grounding wire to the box via the green grounding screw OR use self grounding receptacles and switches and attach the grounding wire to them only. Like you said, it may be up to the inspector on that method, but not on the use of the snap in strain reliefs.
 
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Old 01-07-11, 06:45 PM
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Just to be certain since they're new to me...

The package says each clamp holds 2#14-2 - 10-2 cables. I am using one 12-3 in each clamp. To me that is fine, but since the 12-3 is rounder and 14-2 is flatter, any issue w/these clamps?

And...

If I have to back a cable out, can I just spread the plastic prongs and do that or has the outer shielding been pinched too much w/these?
 
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Old 01-08-11, 06:21 AM
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No issues with the clamps and they are designed to keep you from backing the cable out. Not sure why you would ever have to back your cable out once it is installed. There are no provisions for failure, since they don't fail.
 
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Old 01-08-11, 07:29 AM
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Typically the package will say something like good for use with 2 14-2, 12-2 or 1 14/3 or 12/3.

You can remove the connector from the box with some prying. You can also remove the cable from the connector if you slide a screwdriver between the cable jacket and one of the prongs that grips.
 

Last edited by pcboss; 01-08-11 at 02:13 PM.
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Old 01-08-11, 08:29 AM
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Thanks for the help guys!
 
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Old 01-09-11, 11:00 AM
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Originally Posted by chandler View Post
Yes, you pigtail the grounding wire to the box via the green grounding screw OR use self grounding receptacles and switches and attach the grounding wire to them only. Like you said, it may be up to the inspector on that method, but not on the use of the snap in strain reliefs.
What about running the romex ground wire to the 10-32 screw in the metal box, and then using the self-grounding devices? Is what you mention the only option allowed under the NEC? Is the way I mentioned a code violation?
 
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Old 01-09-11, 11:08 AM
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No, you are correct when using NM. The box must be grounded, whether it be via grounding wire to the grounding screw or via conduit back to the panel. i reread my post and it is confusing to me.
 
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