Internal cable clamps and old wiring

Discussion in 'Electrical Forum discussion & Blog' started by RandomS, Sep 2, 2008.

  1. RandomS

    RandomS New Member

    Messages:
    9
    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. Chris75

    Chris75 Electrician

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    608
    Location:
    Litchfield, CT
    If the sheathing is not long enough, then I would just add some sheathing from a new piece of wire.
  3. Bob NH

    Bob NH In the Trades

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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. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    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. RandomS

    RandomS New Member

    Messages:
    9
    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. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
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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 don’t tell them anything.
  7. RandomS

    RandomS New Member

    Messages:
    9
    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. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
    North Carolina
    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. RandomS

    RandomS New Member

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    9
    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. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
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    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 CANâ€T 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. Chris75

    Chris75 Electrician

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    608
    Location:
    Litchfield, CT
    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. :rolleyes:
  12. jwelectric

    jwelectric Electrical Contractor/Instructor

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    Location:
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    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. RandomS

    RandomS New Member

    Messages:
    9
    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. maintenanceguy

    maintenanceguy In the Trades

    Messages:
    107
    Location:
    Pennsylvania
    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. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    Since you mentioned it, show me the text where its a problem.
  16. Chris75

    Chris75 Electrician

    Messages:
    608
    Location:
    Litchfield, CT
    Its not 1", its 1/4"
  17. jwelectric

    jwelectric Electrical Contractor/Instructor

    Messages:
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    Location:
    North Carolina
    See UL Standard 719 for complete details to the action needed for the sheathing of NM cable

    NEMA 3.13.1 calls for replacement in their NEMA Standards Publication RV-2 which can be found on the NEMA site
  18. RandomS

    RandomS New Member

    Messages:
    9
    Thanks to everyone who has contributed to answering my question. Here's what I think I'll do:

    I believe the old cables are well supported by being stapled to the stud close to the box. Therefore, I'll put holes in the new box just large enough for the old cables' sheathing to pass, in a position where just as much sheathing will be inside the new box as was inside the old box (at least 1/4"). The clamp in that position will remain closed.

    The new cables will simply be installed via the internal clamps, as usual.
  19. maintenanceguy

    maintenanceguy In the Trades

    Messages:
    107
    Location:
    Pennsylvania
    I immediately went to the book to prove you wrong.

    After a little searching I found 314.17.

    Turns out I was wrong. I stand corrected.
  20. Alectrician

    Alectrician DIY Senior Member

    Messages:
    689
    If you think that clamp closes the gap, you are smoking crack. That clamp is about an inch long and the cable is about 3/8 thick. Draw a picture and do the math. The gap in the opening is exactly as big with or without the clamp. Have you ever actually worked in the field?

    And, there is NOTHING wrong with slipping sheathing over wires.

    Guys like JW are just wound way too tightly and do not allow themselves to think freely.

    Here is a compromise. Don't cut the clamp all the way out. Cut it short enough to function but still allow the sheath to be seen. This remanufacturing/altering of listed products of course is highly illegal and dangerous and will likely resuly in a firey death of your entire family.




    OP. I run as many wires as I can thru one opening. It makes the make up cleaner/neater.
    Last edited: Sep 4, 2008
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