Repair improper rough wiring

Discussion in 'Electrical Forum discussion & Blog' started by Jrland, Feb 19, 2018.

  1. Jrland

    Jrland New Member

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    Working on an electrical rough in my home. I put some 90 degree bends in the wire. I have since discovered my error. To repair the wire does it need to be replaced? Don't know if putting a 90 degree bend in the wire would weaken it in those spots.
     
  2. kreemoweet

    kreemoweet In the Trades

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    I don't know of any kind of "wire" that cannot take 90 degree bends, and more. However, there are minimum
    bend radius specifications for each type of product.
     
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  4. WorthFlorida

    WorthFlorida Panama Canal’s new locks!

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    In house wiring there are no bend specification for NM cables but good practices are alway in order. A radius should be that such a cable is not pinched, some slack allowed for movement and prevent chafing to the cable insulation throught a hole, entrance to a box, etc.. Homes with conduit there are minimum bending radiuses depending on the size of the conduit.

    Attaching Electrical Cables to Framing Members:
    https://www.thespruce.com/securing-electrical-cables-1152891

    Similar question but the chapter section mentions may be different. The latest version is 2017.
    http://forums.mikeholt.com/showthread.php?t=67629

    In these charts AWG 10-14 are not specified but these are at a terminal connection.
    http://www.cooperindustries.com/con...-type_metering/ed-minimumwirebendingspace.pdf
     
    Last edited: Feb 19, 2018
  5. Jrland

    Jrland New Member

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    Thanks, so can I shape the cable into a radius in lieu of the 90 degree bend and the cable will be just fine? Thanks for the help, I do appreciate it. WorthFlorida thanks for the links. They are very informative.
     
    Last edited: Feb 20, 2018
  6. Reach4

    Reach4 Well-Known Member

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    If it is already in the 90 degree bend, bending it to a smoother bend will not help. Minimizing further bending will be good.

    If, on the other hand, you are talking about future wiring, then yes, radiusing the bends would be better.
     
  7. kreemoweet

    kreemoweet In the Trades

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    Here's what a (not-up-to-date) copy of the National Electrical Code has to say about bending Nommetallic Sheathed Cable
    (AKA "Romex"): "Bends in Types NM, NMC, and NMS cable shall be made so that the cable will not be damaged. The radius
    of the curve of the inner edge of any bend during or after installation shall not be less than five times the diameter of the cable."
     
  8. Jrland

    Jrland New Member

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    Thanks Kreemoweet. Got it. Reach4 that is exactly what I was wondering. Can I reshape the 90 degree bend to be compliant without worry that there was a weak spot created in the wire? From what you said I assume that I cannot and would need to replace the cable.
     

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  9. Reach4

    Reach4 Well-Known Member

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    I intentionally did not cover that. What I said was that it would be best for the wire to not bend it more. I don't mean to imply that re-forming the bend would be likely to damage the wire. Bending damage is cumulative, and you are probably a long way away from that. If there is not an inspection coming that would cause problems, I would leave it.

    Now lets say that your inspector is looking hard for something to gig you on. The old trick for that is to leave something wrong that is easy to fix. I am not saying that would work with your inspector, but it does with some sadly. But anyway, let's say you want that bend smooth for whatever reason (even OCD) and it is accessible. In that case, you would compute the 5x and find something to use as a mandrel. That could be a small juice can, a big socket, a pipe segment, or whatnot. You would hold your mandrel on the inside corner, and would shape the outside with your fingers or blunt tool.

    For fun, you could experiment with a scrap piece of cable. Bend and try to make a conductor fail. It will be hard to do.
     
  10. Jrland

    Jrland New Member

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    Gotcha Reach4. Really trying to get this right. It will be inspected. I've done so much research but its work practices like this that I would never think to ask about that have been getting the better of me. I've redone work more than 1 time and I would much rather catch any error before I complete the work and call for an inspection. I really do appreciate your help. I put a few pictures in the last post to show examples of what I was asking about. I know I have to make it right or the inspector will look everywhere and I don't want the added stress. Just didn't know if I need to replace the cable or not. Thanks so much for your help! Have a great day!
     
  11. Reach4

    Reach4 Well-Known Member

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    That is much different than I was expecting. I have snipped an image from what looks like your tightest bend, and I think you have plenty of radius at the yellow circle. Maybe where the wire goes through a hole in the wood, you could dress that away from the wood a bit. I was expecting to see something much sharper. img_2.jpg
    If the hole in the wood is where the orange line is, then I would bend the wire away from the underside of that wood, at the green arrow, some to get the radius that the inspector might expect.

    One question that could come up is how do you measure the radius/diameter of an cable with a roughly rectangular cross section? It seems to me that you would use the smaller dimension if the wires are bent as the picture shows. But maybe things are interpreted differently than what I would think. I am not an electrician.
     
    Last edited: Feb 20, 2018
  12. Jrland

    Jrland New Member

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    From what I have read Reach4, The widest dimension is used when calculating the radius. I've been hoping that I could work with the cable a bit in order to have the appropriate radius with the run of the cable that is already installed. It wouldn't be the first time though that I've replaced work that I have completed. This learning curve is killing me!
     
  13. Reach4

    Reach4 Well-Known Member

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    You can work with the cable. Copper is pretty tolerant of extra bending compared to most metals.

    Got it. What is that dimension? If 1/2 inches, that would correspond to a 5 inch diameter mandrel. That sounds like an excessive requirement.

    4 inch PVC pipe is 4.5 inch OD.
     
  14. Jrland

    Jrland New Member

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    what I discovered was that the inner radius requirement was 5 times the diameter, which would be the widest section of a 14/2 wire. A good reference for the calculation would be to imagine a soda can. When I read that, I knew that what I had installed was incorrect and have been trying to figure out if I can rework the cable or if I need to replace it.
     
  15. Reach4

    Reach4 Well-Known Member

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    A soda can is 2.60 inches in diameter. That would be a 1.30 radius. 1.3/5 is 0.26 inches. That soda can idea only works if we are using the thinner dimension, right?
     
  16. Jrland

    Jrland New Member

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    You are right Reach4. It must mean the diameter because everything I read is 2 1/2" but the language always says radius. Weird.
     
    Last edited: Feb 23, 2018
  17. Jrland

    Jrland New Member

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    I thought I would mention why I ask this question about reworking the cable that had a previous 90 degree bend. An electrician said to be careful when installing the staples to secure the cable, that a staple that is driven too tight can cause a arc fault breaker to trip. With that I was wondering if too tight of a bend could cause an arc fault breaker to trip. If there was too tight a bend in the cable, could it be worked out so that it would not trip an arc fault breaker if in fact it could do so. I'm doing a lot of work roughing the entire house. If some of my work tripped an arc fault breaker, how would I find the location that was causing the problem? That's why I was asking about reworking wire. I would much rather avoid the problem if it could occur.
     
  18. Reach4

    Reach4 Well-Known Member

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    It would not.
    I am not an electrician. If I faced that, I would unplug all loads. If the breaker still tripped, I would look for continuity between the disconnect branch wires to each other or ground. There should not be such continuity, although it may be some very high resistance would be acceptable. I would expect normal not-wet wiring to give more than 20 megohm.

    If the ohmmeter on high range did not show a problem, I would get a megger, AKA "insulation tester" that uses 500 volts or more, and check for a problem with that.

    The problem you are worrying about is unusual.

    If the breaker only tripped when something is plugged in to the circuit, I would look to that device.
     
  19. jadnashua

    jadnashua Retired Defense Industry Engineer xxx

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    A staple or clamp applied too tight could actually cause the insulation to be damaged. In the extreme, you could also damage the conductors and/or create a short. IF there's a fault in a cable, it takes specialized tools to locate it unless you can see the entire run, then you have a chance of locating a problem. Arc faults are more common with loose connections verses insulation damage. A megger can test the insulation's integrity. It won't tell you where the problem is along the wire, though. Some of the specialized tools to locate the position by sending a signal down the line and timing the reflection back from the fault.
     
  20. Jrland

    Jrland New Member

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    Thanks for the information jadnashua.
     
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