Damaged NM cable?

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  #1  
Old 02-03-14, 06:55 AM
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Damaged NM cable?

I have a LONG run of 10/3 with ground NM cable running from panel to electric dryer.

I found a small portion of the outter cable damaged, when I pulled back the sheath, one of the conductors is also damaged/nicked/burned.

Do I need to replace entire run, or can a junction box be installed?
 
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  #2  
Old 02-03-14, 06:58 AM
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Unless there is enough slack two junction boxes may be needed. So long as they remain permanently accessible they will be an acceptable solution.
 
  #3  
Old 02-03-14, 07:01 AM
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That's what I was going to just edit.... it appears there wont be enough slack. So how do I fix this?
 
  #4  
Old 02-03-14, 07:13 AM
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Its directly center between two ceiling joists. I would have enough slack perhaps if I can mount a box in the center of the two joists.

I need an idea of both a one box method and a two box method... the slack would be an issue if I mount a single box in the center of the joists?


I also noticed this is 8/3 (on a 30A breaker)... overkill, but is that an issue?
 

Last edited by rards; 02-03-14 at 07:36 AM.
  #5  
Old 02-03-14, 08:48 AM
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Its directly center between two ceiling joists
Put a box on the joists on each side of the damage and cut the cable in the center between the joists. Run new cable (8-3) between the joists and trim the old cable to eight inches in each box. 8-3 is fine on a 30 amp breaker.
 
  #6  
Old 02-03-14, 09:15 AM
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I have never made a splice with such large wire. Should I pretwist them or so something otherwise different than I would with 12or14?
 
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Old 02-03-14, 09:26 AM
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I would have enough slack perhaps if I can mount a box in the center of the two joists.
If you can cut the damaged piece out of the cable, install one box and have at least 6" of each cable end inside the box to work with, you can do this with one box. 8" of cable if using a 4" square box.

Should I pretwist them or so something otherwise different than I would with 12or14?
All solid electrical conductors are spliced by twisting them together. A wire nut protects the splice. In this case you'll want to use the big blue or gray wire nuts.
 
  #8  
Old 02-03-14, 09:33 AM
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Why the funny confused face nashkat?

Was wondering if something like a terminal block or split bolt is necessary....plus this is stranded big stuff and I wasn't sure if they pretwist correctly?
 
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Old 02-03-14, 10:24 AM
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Why the funny confused face nashkat?
My confusion was that I read
Should I pretwist them or so something otherwise different than I would with 12or14?
as saying that you believe that #12 and #14 conductors don't need to be twisted together. That's why I said "All solid electrical conductors..."

Was wondering if something like a terminal block or split bolt is necessary....
No, just the large wire nuts.

plus this is stranded big stuff and I wasn't sure if they pretwist correctly?
Well duh, of course it is. Thanks for the reminder.

To answer your question, many folks like to tighten the twist in stranded conductors and then twist them together the same way they would if they were solid conductors. I've found though - and this is just my own experience - that I get a better connection in the splice if I untwist the conductors so they look like brushes and then twist those two brushes together. The brushes will usually interweave and mesh into each other when it's done that way, IMX.
 
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Old 02-03-14, 10:28 AM
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No, no split bolts or other special connectors needed. Wire nuts are okay. If the box(es) are metal you do need to pigtail the ground to the box. Not sure of pigtail size. Pros can answer that one.
 
  #11  
Old 02-03-14, 10:36 AM
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As for the grounds Ray its NM so if I use metal box(es) I would just splice the grounds in the box as well (2 wires in and out)? Im taking it as your saying I need a 3rd wire pigtail to box too?
 
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Old 02-03-14, 12:10 PM
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Im taking it as your saying I need a 3rd wire pigtail to box too?
Yes. You can do that with #10 wire.
 
  #13  
Old 02-03-14, 12:31 PM
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I would imagine this type of damage was done during installation, judging by the date on the cable back in 2002. And judging from the burn, I would think the breaker would have tripped at that point. But Im wondering why the breaker never tripped when using the dryer all this time?

The red conductor has a nick in the insulation and there is scortching. But it doesn't look like the other wires insulation was damaged and there is still paper I think on the ground. So where does the scortch come from?

If I didn't happen upon it and see the damage, how would have likely been discovered? Do you think the damage wire would have burned thru the paper and shorted to ground or would that wire just failed and I would only be getting 120 at the dryer? Or worse, a fire? I was actually touching the energized bare spot before I realized what it was....

p.s.- I had a raco bracket on hand but it isn't the kind that has a threaded connector to go thru the center knockout.... it has a screw and a little u shaped washer and I am having a hard time figuring out if that works with a 4x4 box.

. If I go the route of mounting a box in the center of the joists, would a 2x4 screws driven at angle to hold it in place be sufficient?
 
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Old 02-03-14, 12:50 PM
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would a 2x4 screws driven at angle to hold it in place be sufficient?
Yes.

.
 
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Old 02-03-14, 01:01 PM
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judging from the burn, I would think the breaker would have tripped at that point. But Im wondering why the breaker never tripped when using the dryer all this time?
No condition existed to trip the breaker. There was no short and no overload.

The red conductor has a nick in the insulation and there is scortching. But it doesn't look like the other wires insulation was damaged and there is still paper I think on the ground. So where does the scortch come from?
Maybe that is part of the original damage. Maybe, if the conductors were damaged enough, There was more heat generated there than the insulation was made to handle.

If I didn't happen upon it and see the damage, how would have likely been discovered? Do you think the damage wire would have burned thru the paper and shorted to ground or would that wire just failed and I would only be getting 120 at the dryer? Or worse, a fire?
Probably not a fire.

I had a raco bracket on hand but it isn't the kind that has a threaded connector to go thru the center knockout.... it has a screw and a little u shaped washer and I am having a hard time figuring out if that works with a 4x4 box.
Can you post a picture of it, or search for it online - maybe on Raco's site? I sounds like a saddle connector for MC or Gernfield, except that you call it a bracket and say that you don't see how it might work with a 1900 box.

If I go the route of mounting a box in the center of the joists, would a 2x4 screws driven at angle to hold it in place be sufficient?
IDK. What's a 2x4 screw? What are your floor and subfloor made of and how thick are they?

How are you planning to get 8" of each cable end inside the box if you don't mount a second box?
 
  #16  
Old 02-03-14, 01:09 PM
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Its just like this one but doesn't have the male threaded piece you see in the photo (which I assume goes thru the top 1/2" knockout)... just the washer and like a pan head screw. The screw fits thru a hole in the box but I am not sure if that's the proper way to mount it.

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How are you planning to get 8" of each cable end inside the box if you don't mount a second box?
I can get 4 maybe 6 inches I think of slack in the box, working with some scrap #8 and I am realizing I will need more than that... this stuff is very hard for me to work with. The 2 box route looks to be the way to go but now I gotta sweat making 4 big joints.

Just to confirm, I will need to bring 8/3NM thru the 3/4" knockouts with 3/4" connectors.
 
  #17  
Old 02-03-14, 01:51 PM
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Its similar to this but the one I have doesn't have the male threaded piece... just the washer and like a pan head screw. The screw fits thru a hole in the box but I am not sure if that's the proper way to mount it.
That might work if you had either 2 or 4 of the mounting pieces on it.

I can get 4 maybe 6 inches I think of slack in the box, working with some scrap #8 and I am realizing I will need more than that...
You need at least 8" of cable showing on each cable inside each box. If your joists are 2xs 16" o.c. and you can cut the cable exactly halfway between them, that gives you + 7-1/4" of cable off the face of each joist to where the two ends will barely touch each other.

If I were doing this, I'd be thinking about mounting a box in the joist bay on each side of the damage and pulling the cable ends back to there to splice them to a repair piece.

this stuff is very hard for me to work with.
Yeah, it's kind of an awkward size. It's also like any other conductor - it's easier to work with if you have a bit more than you need.

The 2 box route looks to be the way to go but now I gotta sweat making 4 big joints.
Four splices of #8 and two of #10 doesn't sound too bad. Curling the #10 pigtails around the ground screws might be a bit of a challenge.
 
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Old 02-03-14, 02:04 PM
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Curling the #10 pigtails around the ground screws might be a bit of a challenge.
Solid will be easier or you can crimp on a open end ring connector.
 
  #19  
Old 02-03-14, 02:20 PM
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Another option I have is replace about 20' from panel to damage. Its about 30' ft in the other direction.

Obviously more costly but is that a significantly better idea than the two box idea?

How would a service electrician do it if called to the house?

8-3 is fine on a 30 amp breaker.
I know its OK to overfuse in this situation but another thing I was thinking. Are 30A breakers designed to use #8? I have 1" GE brand breakers.

Another confusion... 8/3 with ground used with a 30A dryer plug... I didn't take it apart to check but what is the white wire used for then? Or is that the third prong and the bare ground just grounds the box?
 

Last edited by rards; 02-03-14 at 03:07 PM.
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Old 02-03-14, 03:47 PM
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Are 30A breakers designed to use #8?
Yes and almost certainly #6 because the longer the distance of the run the larger the cable so breaker design takes that into consideration.
8/3 with ground used with a 30A dryer plug... what is the white wire used for
Most dryers are 120/240. Most manufacturers build basically the same dryer for gas or electric heat. All have the same 120 volt motor and 120 volt controls. The only difference is they stick a gas burner in one and a 240 volt heat coil in the other.
 

Last edited by ray2047; 02-03-14 at 05:33 PM.
  #21  
Old 02-03-14, 04:23 PM
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How are you planning to get 8" of each cable end inside the box
Generally I know it will be easier to work with, but why 8" as opposed to the standard 6"? (or less as I usually get dealt when repairing stuff).
 
  #22  
Old 02-03-14, 04:46 PM
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why 8" as opposed to the standard 6"?
The standard is actually 4" plus the measurement across the face of the box. Since a 1900 box is 4" x 4", that's 8". That's the minimum, of course. You can make it longer if you want to.
 
  #23  
Old 02-03-14, 06:24 PM
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The code requires 6" minimum of free conductor in the box from each cable. You are probably going to need 2 boxes or to run a new portion of the run.

To splice just line up the ends of the wires and add the splice cap.
 
  #24  
Old 02-04-14, 04:51 AM
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You are probably going to need 2 boxes or to run a new portion of the run.
If there was access to about 20 ft back to the panel, then the new portion of the run would be the preferred method right?

To splice just line up the ends of the wires and add the splice cap.
Theres no way those #8's are going to twist in a wirenut without some sort of prepping....

I was experimenting with Nashkats brush technique and it seems to work but I have never worked with nor have seen what a properly twisted large wire splice like this should look like.....
 
  #25  
Old 02-04-14, 10:04 AM
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Got it done this morning. Went smooth. I was able to undo the rest of the cable and create enough slack to mount a single box on one of the joists. I then had at least 6-8" of wire to work with. I used a 4x4x2 1/8 box with the stud bracket on the side and mounted it to the joist. I used the 1/2" knockouts and appropriate cable clamps.

I was getting 120 from each hot to the neutral and 120 from each hot to the ground and 240 between the hots. I connected the ground with a pigtail to the box as instructed and used large Gardner and Bender Blue wire nuts.

Hopefully I didn't loosen the device on the other end with my pulling and tugging.... but it appears to be functional now.
 
  #26  
Old 02-04-14, 10:17 AM
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Thank you for letting us know how it went.
 
  #27  
Old 02-04-14, 12:20 PM
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Glad you got it done, and thanks for the update.

Hopefully I didn't loosen the device on the other end with my pulling and tugging.... but it appears to be functional now.
??? All cables should be secured within 8" of any box that they enter. That's required in order to prevent their being pulled loose from a connection inside the box. Is your cable secured there?
 
  #28  
Old 02-04-14, 03:53 PM
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??? All cables should be secured within 8" of any box that they enter. That's required in order to prevent their being pulled loose from a connection inside the box. Is your cable secured there?
The insulated staples were removed to give slack while working and getting everything in place. I used a temporary one right at the outlet up stream while doing the work.

Pulling the old staple bent them to much for reuse so I used some new plastic Gardner and Bender straps to resecure the cable when I was done.
 
  #29  
Old 02-04-14, 04:45 PM
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OK, I'll hope along with you that you didn't mess up anything inside a box while you were working. It sounds like you left the cable secured to the box the whole time. If you can't see that it ever moved relative to the clamp at the box it's probably fine.
 
  #30  
Old 02-05-14, 04:37 AM
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Nashkat1


OK, I'll hope along with you that you didn't mess up anything inside a box while you were working. It sounds like you left the cable secured to the box the whole time. If you can't see that it ever moved relative to the clamp at the box it's probably fine.


Save your hope for the lottery Nashkat... again, I used a few temporary staples to secure it while working.....so I should be good to go.

Thanks for the help too Ray, I would have missed the pigtailing grounds if it wasn't for you mentioning it.
 

Last edited by ray2047; 02-05-14 at 06:38 AM. Reason: Remove un-needed tag.
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