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Thread: Internal cable clamps and old wiring

  1. #1

    Default Internal cable clamps and old wiring

    I am replacing an existing fiberglass double-gang electrical box with a PVC triple-gang old-work box (a Carlon B355R box: http://carlon.com/Brochures/7F61.pdf). The new triple-gang box has internal plastic cable clamps of the type that apply constant pressure to the NM cable sheathing to hold the cable in place. You can see these clamps pretty clearly in Carlon's brochure.

    With new cable, these clamps seem to work pretty well. It's easy to pull the cable through the clamp, and it holds the sheathing tightly and safely (to my eye). However, I have to bring the existing NM cables (which are 14/2 of circa 1986 vintage, in good shape) into this box, and of course they already have the sheathing stripped back. The sheathing just barely reached into the old box, and the new box is deeper. The different geometry means that the sheathing on the old wires doesn't reach the new box's cable clamps (by about an inch). Instead, the clamps would clamp on each individual wire's insulation, even biting into the insulation a bit (the plastic clamps have sharp edges). And of course the individual wires don't want to come through the clamp properly centered, they want to sneak around the sides and generally misbehave. This seems like bad news to me.

    Any advice on dealing with this?

  2. #2
    Electrician Chris75's Avatar
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    If the sheathing is not long enough, then I would just add some sheathing from a new piece of wire.

  3. #3
    In the Trades Bob NH's Avatar
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    If the sheathing is too ragged to get new sheathing in place you might add some tape held in place by shrink-tubing.

    I would like to see the new sheathing overlap the old. If you can slip sheathing over the wire then it probably is a bit loose and those plastic tabs don't really clamp effectively. Even with new sheathing over the cable I would add shrink tubing to keep it in place.

  4. #4

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    90% of the time in rework I tear out the clamps with needlenose.

    The cable is stapled to the stud. Unless a leprechaun gets in there and pulls the cable out, it's not going anywhere.

    As long as the sheath is in the box, you're good.

  5. #5

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    Alectrician, I think you have an excellent point. And that suggestion certainly is easy to implement! I can use the clamps where new cable comes into the box, and remove the clamps on the old wiring openings.

    One follow-up question: Once the clamp is removed, it leaves a pretty big opening. Would it be better to bring two of the old cables in through the same (nearest) opening, thus maximizing the amount of sheathing in the box, or is it better to use separate openings for each cable? (I wouldn't clamp two cables in the same clamp, but now we're talking about unclamped openings.)

  6. #6
    Electrical Contractor/Instructor jwelectric's Avatar
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    Just what is the purpose of having the box in the first place?

    Could it have anything to do with confinement of any type of arc that could occur?

    What is being told to an untrained person is to just forget about the confinement requirement that the box is installed for in the first place or to just jury rig something that might fool someone looking in but does nothing for containment of an arc or the protection of the conductors contained therein.

    Then we wonder just how some of the installations were achieved the way they were.

    Please people if you are not going to tell someone how to do something correctly then just donít tell them anything.

  7. #7

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    jwelectric, that's a great point about confinement. In light of that, how best to bring the old wiring (with the sheathing already stripped) into the box, while maintaining the integrity of the box? Replace the missing sheathing with shrink tubing, as suggested earlier?

    This is why these forums are so helpful!

  8. #8
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by RandomS View Post
    jwelectric, that's a great point about confinement. In light of that, how best to bring the old wiring (with the sheathing already stripped) into the box, while maintaining the integrity of the box? Replace the missing sheathing with shrink tubing, as suggested earlier?

    This is why these forums are so helpful!
    You have only two code compliant options.

    1- replace the nonmetallic cable
    2- move the box to where the existing cable enters the box

    The idea of trying to replace the sheathing is bogus as anything I have ever heard in my entire life. The sheathing is required to be continuous from start to finish and repair is not allowed in any circumstance.

    Anything short of these two methods is nothing short of dumb, stupid, crazy or any other adjective one would like to describe the installation. One that comes to mind to describe those things that have been stated so far sounds like some type of male to female bonding that is aimed toward the sky or some other upward direction.

  9. #9

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    I hear you.

    With that in mind, how do you replace a box with one of these old-work boxes? I'm assuming that most of the time, replacing all of the cables entering the box is not a practical option, and neither is moving the box (which wouldn't help anyway -- cables enter from both top and bottom).

  10. #10
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by RandomS View Post
    I hear you.

    With that in mind, how do you replace a box with one of these old-work boxes? I'm assuming that most of the time, replacing all of the cables entering the box is not a practical option, and neither is moving the box (which wouldn't help anyway -- cables enter from both top and bottom).
    Again experience comes into play here. A different type of box could solve your problem or even the installation of another box either above or below could solve your problem.

    What you CANĒT do is add sheathing to the cable or any other type of junk such as heat shrink or tape to make it look a little better.

    When I bid this type of work I will include the proper method of installation in the bid then it is up to the person paying the bill to decide if they want me doing their work or not.

    What I will not do is some of the junk that has been posted here and neither should you.

    If there is conductors entering the bottom of the box then simply add a receptacle under the switch and use that box for some of the joints with a new cable from the receptacle up.

  11. #11
    Electrician Chris75's Avatar
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    Quote Originally Posted by jwelectric View Post

    The idea of trying to replace the sheathing is bogus as anything I have ever heard in my entire life. The sheathing is required to be continuous from start to finish and repair is not allowed in any circumstance.
    No its not, I called southwire on this, they say its not required and tape is perfectly fine, so at least I did my part of the homework.

  12. #12
    Electrical Contractor/Instructor jwelectric's Avatar
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    Quote Originally Posted by Chris75 View Post
    No its not, I called southwire on this, they say its not required and tape is perfectly fine, so at least I did my part of the homework.
    Hey I called the fellow down at the local service station and he said...............

    I think that you would be better to call someone responsible for testing the cable than someone that manufactures the stuff. All that Southwire is interested in is sales.

    Do some more homework and see what UL or NEMA has to say about damaged cable.

  13. #13

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    I can bring the old cable into the new box with the sheathing intact. I just can't do it through the new box's internal cable clamp -- it won't reach. What I can do is make a hole just big enough for the sheathing to pass through, right next to the clamp. There won't be any more of an opening in the box than there would be if I used the cable clamp (which after all, is far from airtight).

    The obvious downside is that the old cable won't be secured to the box. Given that it's stapled to the stud a few inches outside the box, how big a deal is this actually? What is the scenario where this would cause a problem?

  14. #14
    In the Trades maintenanceguy's Avatar
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    NEC requires 1" of sheathing to be inside the box. Frankly, any sheathing showing within the box would satisfy me.

    How about ignoring the integral cable clamps, making a 1/2" knockout and using a standard romex connector. That gets you an extra 1/2".

    Or, the right way would be to install a box above and below this box and use them as splice boxes to get new wire to your replacement box. A box near the ceiling and one near the baseboard painted or wallpapered to match (but not covered over and concealed) wouldn't even be noticed.

  15. #15
    Electrician Chris75's Avatar
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    Quote Originally Posted by jwelectric View Post

    Do some more homework and see what UL or NEMA has to say about damaged cable.
    Since you mentioned it, show me the text where its a problem.

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