I did a home project this weekend envolving 12/3 w ground romex.After the installation I went to turn on the breakers,Which the breaker for the red conductor tripped immediately.After investigating I noticed the short was inside the cable between the red and the bare ground,where it was clamped by the romex connector.I did not tighten the clamp with force and makes me leery of the suitability of the insulation on modern day 12/3 w ground.I've had this happen once before to me and was wondering if anyone has had the same problem? As thin as the insulation is on the conductors I wouldnt be surprised if this damage is present in a lot of installs that doesnt show up for the simple fact that most residential boxes are plastic,Mine were metal 4 squares.
nm cable
- Thread starter jap2525
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bill addiss
Senior Member
Re: nm cable
I've noticed this for a few years with 14/3 NM. IMO cable clamps need to be redesigned somewhat to be more compatible with new cable construction.
BTW, the problem you describe would show up whether the box was made of plastic or metal because the clamp is causing a direct short in the cable itself.
Bill
I've noticed this for a few years with 14/3 NM. IMO cable clamps need to be redesigned somewhat to be more compatible with new cable construction.
BTW, the problem you describe would show up whether the box was made of plastic or metal because the clamp is causing a direct short in the cable itself.
Bill
jeff43222
Senior Member
- Location
- Minneapolis, Minnesota
Re: nm cable
Theoretically the cable should be able to withstand the metal cable clamp, but then there's the real world.
Last year I wired a dryer circuit with 8/3 into a metal receptacle box and ran into the same problem. When I turned the breaker on for the first time, I heard a boom near the dryer, found a nice new burn hole in the metal clamp, and the breaker tripped. Now my policy is to tighten NM clamps only until the cable doesn't move freely. Anything tighter runs the risk of causing a short from pinching.
Theoretically the cable should be able to withstand the metal cable clamp, but then there's the real world.
Last year I wired a dryer circuit with 8/3 into a metal receptacle box and ran into the same problem. When I turned the breaker on for the first time, I heard a boom near the dryer, found a nice new burn hole in the metal clamp, and the breaker tripped. Now my policy is to tighten NM clamps only until the cable doesn't move freely. Anything tighter runs the risk of causing a short from pinching.
Re: nm cable
It would be nice to be able to use a cordless and (put the screws to it) and a lot faster,I suppose most do, but I,like you, always tighten them by hand for fear of damaging the cable.I do the same on receptacle and switch terminations.I know a lot of guys who use cordless for this but I like to feel the torque myself.
It would be nice to be able to use a cordless and (put the screws to it) and a lot faster,I suppose most do, but I,like you, always tighten them by hand for fear of damaging the cable.I do the same on receptacle and switch terminations.I know a lot of guys who use cordless for this but I like to feel the torque myself.
buck33k
Senior Member
- Location
- Washington state and North Carolina
Re: nm cable
I have gotten away from the metal romex connectors and use ETD RC-50 plastic snap-in connectors for metal boxes and panels. They are UL approved for 2 cables or one 10/2. Much faster, better looking panel make-up, and they do not crush the cable.
I have gotten away from the metal romex connectors and use ETD RC-50 plastic snap-in connectors for metal boxes and panels. They are UL approved for 2 cables or one 10/2. Much faster, better looking panel make-up, and they do not crush the cable.
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: nm cable
Nothing wrong with them plastic connectors.
And set clutch on 10 for devices and everything should be fine.
Nothing wrong with them plastic connectors.
And set clutch on 10 for devices and everything should be fine.
electricman2
Senior Member
- Location
- North Carolina
- Occupation
- Retired Electrical Contractor
Re: nm cable
10 on my Dewalt would strip device screws. More like 4 or 5.
jimwalker
Senior Member
- Location
- TAMPA FLORIDA
Re: nm cable
so start with a low number and if you can hand tighten more after the cordless then raise it.I did break a switch yesterday with my cordless but that was my fault as i forgot to take it off of drill position.Even if not faster it is a lot easier on the installer
[ October 25, 2004, 04:53 PM: Message edited by: jimwalker ]
so start with a low number and if you can hand tighten more after the cordless then raise it.I did break a switch yesterday with my cordless but that was my fault as i forgot to take it off of drill position.Even if not faster it is a lot easier on the installer
[ October 25, 2004, 04:53 PM: Message edited by: jimwalker ]
macmikeman
Senior Member
- Location
- Planet macmikeman
Re: nm cable
I hand tighten device terminal screws and use my cordless for the device mounting screws. I prefer to know by feel that the screw is tight. This may take me 10 seconds more per device, but I sleep good at night.
I hand tighten device terminal screws and use my cordless for the device mounting screws. I prefer to know by feel that the screw is tight. This may take me 10 seconds more per device, but I sleep good at night.
petersonra
Senior Member
- Location
- Northern illinois
- Occupation
- Semi-retired engineer
Re: nm cable
is this a "legal" method?
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