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Old 12-03-2009, 11:09 PM   #1
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Is metallic ceiling box OK for Romex?


Hi;
I just installed a new light fixture on my back porch. The one that was there before had no box at all, and there is another cable leaving this fixture to an outdoor light.

So, I installed a metallic ceiling box (old work). I needed a metallic one because the cable feeding the light is old BX.
The cable to the outside light is Romex.

When I looked at the box, I found one standard knockout in the bottom, and two more on two sides of the box. On the sides that do not have a standard knockout, there are two sets (each side) of smaller knockouts which have a clamp inside the box.

My first thought was that I could use this inside clamp for the Romex; It would have been easier to install the box with the Romex coming into this clamp because it's at the bottom of the box, rather than higher up as the standard knockouts are.

But looking more carefully, I decided that these smaller knockouts were not intended for NM, but for BX (AC, or whatever).
So I used one of the standard knockouts and a standard metallic NM clamp.
It worked out fine, but I had to manipulate the box and the cable without pulling the clamp into the box until it was in the ceiling, or it never would have cleared the cutout.

I have seen metallic boxes with internal clamps that were intended for NM, but I believe the clamps looked different, and maybe the shape of the knockout as well.
But I needed the old-work box with ears, so this was the only one available.

Thanks for your help

FW

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Old 12-03-2009, 11:22 PM   #2
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Is metallic ceiling box OK for Romex?


Like you surmised there are different clamp available in metal boxes. You sound like you just picked up one with the wrong style clamps.

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Old 12-04-2009, 04:57 AM   #3
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Is metallic ceiling box OK for Romex?


Is this similar to what you used?



Those are clamps for BX or MC cable, and can be removed completely if not utilized. Using standard connectors in the other knockouts is fine.
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Old 12-04-2009, 06:29 AM   #4
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Is metallic ceiling box OK for Romex?


Quote:
Originally Posted by kbsparky View Post
Is this similar to what you used?



Those are clamps for BX or MC cable, and can be removed completely if not utilized. Using standard connectors in the other knockouts is fine.
Like the pic kb has, there are other type of clamps inside metal boxes that are approved for nm cable.
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Old 12-04-2009, 10:50 AM   #5
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Is metallic ceiling box OK for Romex?


The box had the clamps without the extension in front. They almost looked like Romex clamps, but not exactly.
I was concerned about the Romex jacket being cut on the edge of the knockout, but that is probably just my being a little over-cautious.

Here is a photo of the clamp.



It was those extra tabs on the bottom that made me think it was an MC clamp rather than an NM, figuring that the tabs were for grounding.

FW
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Old 12-04-2009, 11:09 AM   #6
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Is metallic ceiling box OK for Romex?


That clamp is fine for use with nm cable.
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Old 12-04-2009, 12:03 PM   #7
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Is metallic ceiling box OK for Romex?


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That clamp is fine for use with nm cable.
OK.
I'll keep that in mind for next job.

Thanks

FW

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