using NM cable with single gang metal box

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Old 04-04-07, 11:37 AM
ddr
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using NM cable with single gang metal box

This is going to be a really newbie question, so let me offset some of my embarrassment by saying that Iíve always used AC cable here in New York City either because it was required until recently, or because everything else was AC / metal boxes so I just kept everything uniform; the only time Iíve worked with NM cable was at a friendís house in New Jersey and he had plastic boxes. Okay, that said:

I had always thought that when using NM with single gang metal boxes, you needed to use an NM cable clamp and locknut through a 1/2Ē knockout because the rear knockouts with internal clamps had rough edges that could damage NM cable. Is this the case? If not, do you need to file down were the knockout snaps from the box or use some kind of bushing when using NM?

No ribbing please; Iím embarrassed enough to have to ask this...

Thanks in advance.
 
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Old 04-04-07, 11:42 AM
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Plastic boxes either have a built in cable "clamp" or do not need one.
 
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Old 04-04-07, 11:52 AM
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Those little plastic flaps on the plastic boxes should not be removed, but only bent slightly to allow the cable to pass through. You can just push the cable through and it will push aside the flaps just the right amount.

Because the cable does not clamp to the box, code requires you to staple it within 8 inches of of the box (rather than within 12 inches as for metal boxes with clamps).
 
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Old 04-04-07, 11:55 AM
ddr
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Bob,

Thanks for the quick reply, but I was asking about the proper way of using NM cable with a metal box. Would appreciate any help.
 
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Old 04-04-07, 12:08 PM
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Sorry, I misread your post.

Metal boxes require a cable clamp. Some metal boxes have an internal cable clamp that can be used, others need one added. The ones you add are sometimes called Romex connectors.
 
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Old 04-04-07, 01:16 PM
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Bob,

Thanks for the reply. The boxes I got at the big box store have the type of clamp that works with either armored or non-metalic cable (you snip off the part of the clamp that has rings to hold the anti-short bushings in the armored cable) which leaves a simple pressure plate to hold the NM cable. I was just concerned if the edges of the knockout holes are considered abrasive and needed any special bushing.

Thanks again.
 
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Old 04-04-07, 08:27 PM
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You may trim them. (I didn't say that) There are special clamps for NM boxes (2 types of boxes at the store, Look at the clamps).
If You use metal boxes they MUST be grounded. They also sell the grounding pig tails, These connect from the box to the ground wire and the device (switch,rec,etc).
 
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Old 04-05-07, 03:03 AM
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Just be carefull to not overtighten the connector.
 
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