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I needed to replace an electrical wire with a longer one so I could move an electrical outlet. When I went to cut away the outer rubber cover of one of the wires with a utility knife (yes, dumb, I know), I accidentally shaved off a wee little sliver of copper from the wire. Everything works fine, but I am wondering if it's something serious that could affect the transfer of electricity or cause other problems.

It has since been installed, so I don't remember if it was the hot, neutral, or ground at this point. Should I redo it with a different wire? I can't cut off any more of the wire as I didn't allow myself that much slack.

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if wee little sliver is like a nick/ hairline.. then its fine.. if it was about a 1/4 or more of the diameter of the cable deep.. then you would replace it.. you might know about it.. but the next person does not.. If it gets close to the full load of the wire it could cause a fire.. (possibly also change the plug to a single socket and mark it clearly for use of 1 applciance only - eg kettle, or fridge.. no more) PS I like your beard –  ppumkin Jan 20 '12 at 21:36
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3 Answers 3

up vote 4 down vote accepted

If you are talking about something the size of a splinter then you have no problem. I doubt if you shaved enough off to change the ampacity of the wire. The main reason not to use a knife (other than safety) is scoring the electrical wire and making it easier to break off. Wire strippers normally go enough of the insulation to make it weak enough to come off with little effort.

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I agree with lqlarry in that if it's just a small splinter/nick then there is likely not much risk. However, if the wire had a deeper nick or multiple cuts you would want to cut off the damage and re-strip the wire. The reason being is that damage to the wire increases resistance. Increased resistance creates heat, and heat eventually can cause fire. There are safety margins built into the electrical codes, but considering the relatively small diameter of the wire, it doesn't take much damage to effect a couple percent of the diameter, and this can be a problem.

If you have any doubts, cut off the damaged part and strip it with a proper wire stripper.

If slack is a problem you can use a wirenut and a spare piece of wire to extend the length enough for the outlet.

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You can extend electrical wire with a simple wirenut? Don't you need a junction box for that, though? –  oscilatingcretin Jan 20 '12 at 12:41
    
I assumed he was working in a box already, but otherwise, yes you would be correct –  Steven Jan 20 '12 at 13:13
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I know of 3 reasons to be concerned about nicks when stripping a conductor:

  1. It increases heat at this point. Heat causes parts to expand & contract, loosening connections over time, producing yet more heat. Hot enough and it will start a fire.

  2. It's a weak spot, a "stress riser". If the wire flexes a lot, it is more likely to break at this point, which is potentially a dangerous condition (e.g. if the hot wire breaks, shifts, and makes contact with the body of an ungrounded appliance.) Of course, solid conductors are usually only used in installations that don't move, and stranded conductors don't fatigue as easily.

  3. A friend (at a party, no less!) told me that, since high voltage moves along the surface of a wire, a sudden decrease in thickness could be a problem. I don't have anything hard to back this up, so I don't know if it would apply in this situation.

If the nick is very small, you're probably fine. If there's nothing making the wires flex, they probably won't break. If you don't run at maximum amperage at maximum allowed temperature, then it may not overheat. Etc.

As indicated in other answers, you don't have to cut all the way through the insulation to remove it. If you get close, it will tear easily. Once you build up tension in the insulation, you can touch it with a sharp edge and it will part easily.

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Would downvote if I had the rep. Don't speculate on things you don't know and can't be bothered to research. #3 is wrong for so many reasons. The so-called skin effect operates on high-frequency signals. At 60 Hz, the skin depth is ~0.36 inches, which is obviously way thicker than a wire. Even if you didn't know that, it should be obvious that a shaved wire still has a surface. If skin effect were actually an issue, it would actually be an argument that a nicked wire is okay!... –  ThePopMachine Jan 20 '12 at 7:18
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...(contd) The problem with a nicked wire is that a smaller cross-section raises resistivity (sans skin effect). See here: daycounter.com/Calculators/SkinEffect/… –  ThePopMachine Jan 20 '12 at 7:18
    
@ThePopMachine: Thank-you for that useful additional information. I wasn't claiming to know anything about #3; I'll clarify my post. –  Jay Bazuzi Jan 20 '12 at 19:53
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