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Old 06-24-2008, 09:13 PM   #1
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New wire in old cable?


Hi;
Has anyone had any luck with pulling new THNN wires through an old BX?
It would be a way to avoid having to open walls/ceilings to replace the cable itself.
The existing BX is #14. I would try to pull three (black, white, green) THNN wires for the lights in the ceilings where access from upstairs is not possible.

I would imagine that this could work if there are no sharp (RA) bends in the cable. I often see RA BX clamps at the boxes, so these would be very difficult unless I can get the old box out.
Then, if I can get the box out, I might as well pull a whole new cable, right?

FW

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Old 06-24-2008, 09:34 PM   #2
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New wire in old cable?


Good luck. I've never before heard of anyone trying this so I wouldn't even know where to look in the NEC regarding its legality. You would have hells own time removing the old wires (esp. if they are cloth covered). It can be difficult to fish wires through a piece of 1/2" greenfield (which has a considerably larger ID) with a few bends in it. I think that you're better bet would be to try connecting new MC cable to the old BX (splicing the wires together) and using the BX to pull in the new armored cable. There is no way in "H" that this will work if there is even one strap on the old stuff though.

Best bet is to bite the bullet and pull in/fish new MC cable. If you have attic/basement access, this can be rather easy actually.

Take care,
Jimmy

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Old 06-24-2008, 09:49 PM   #3
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New wire in old cable?


it's not legal. BX is made as a cable and it is not legal to alter it. Altering it would make it not BX anymore.

On top of that, what you essentially are doing is using the metal sheath as flexible metallic conduit, which is not allowed in sizes under 1/2 except in a very few applications.
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Old 06-25-2008, 07:18 AM   #4
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New wire in old cable?


Thanks for your advice. I read about doing this somewhere, and was interested to find whether anyone had actually done it. I'm not really surprised that it's not legal.
I'll have to find where I read it, and send a comment to the author.

FW
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Old 06-25-2008, 10:24 AM   #5
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New wire in old cable?


Follow naps instructions and warnings. He is absolutely correct.
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