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I use a small cutter made for max 14 gauge wires, but I'm bad at removing insulation, it takes me a bit of time to get it right, so I end up cutting and repeating, because I see scratches on copper wire were I cut the insulation. Should I ignore it? How bad are these scratches or marks? These are power works behind sockets.

Blurry photo that doesn't show scratchmarks

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    You know that's not a very useful photo, right?
    – RedGrittyBrick
    Dec 5, 2017 at 17:40
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    @RedGrittyBrick it's clearly a match melting a straw. Not sure what that has to do with nicked wires.
    – Brad
    Dec 5, 2017 at 20:22
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    @WayneConrad OK but you need to explain why that's relevant. I doubt the asker is proposing to bend the wire back and forth many times after installing it.
    – David Richerby
    Dec 6, 2017 at 14:00
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    @DavidRicherby Well, that would turn my comment into an answer :) When installing wiring, it gets pushed, folded, and bent, either now, or later when someone else goes back into the wiring box to do something. It doesn't take many bends to break a nicked wire.
    – Wayne Conrad
    Dec 6, 2017 at 14:11
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    Unless it's really deep, a scratch along the length of the wire is of no consequence. What is a potential problem is a fairly deep nick across the width of the wire, as that will create a stress point if the wire is subsequently bent (as when you are shoving the outlet back into the box)
    – Hot Licks
    Dec 7, 2017 at 1:16

6 Answers 6

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Minor superficial marking is just that. Unimportant. Deep nicks around the circumference create weaknesses. Those would cause problems. Redo.

With the right tools, careful use and a little practice, you will be able to strip insulation without nicking or scratching the copper.

Blurry photo
Suitable tools, in the same spirit as photo in Q :-)

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    This is amazing.
    – JPhi1618
    Dec 5, 2017 at 19:03
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    Well played, sir. Well played...
    – Machavity
    Dec 5, 2017 at 19:40
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    Since this photo has nothing in focus (as opposed to focusing on the background like OP), I thought something was wrong with my browser or connection. Well done.
    – Engineer Toast
    Dec 6, 2017 at 19:10
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    I had to join this community just so I could upvote this. Bravo.
    – sirjonsnow
    Dec 7, 2017 at 13:38
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    You win StackExchange for today...
    – Graham
    Dec 7, 2017 at 13:44
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Obligatory X answer: If you have to ask if the nick is bad enough, it's bad enough.

It's not you. It's the piece of junk wire stripper. There are a LOT of really terrible wire strippers out there, either in the $5 tool bin, or they come with variety packs of crimp terminals.

If you only have occasional work to do, take WGroleau's advice and roll an exacto knife around the edge of the wire, pressing just barely enough to penetrate the insulation, not nick the wire appreciably.

Otherwise, go out and buy a really good one. We're talking $12-15. Irwin is the lowest quality I would consider, and not their bottom-end unit either.

It should have a mystery hole about 1/4" from the edge of a side. Bolt shears are nice but not necessary. Having a terminal crimper is usually the mark of a junky cheapie, though it's perfectly possible for a fine tool to have it.

I know it's easy to sit here and spend your money. Rest assured I don't do it lightly. You'll thank me...

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    You, in all honesty, do not answer the question.
    – yo'
    Dec 5, 2017 at 18:23
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    I disagree. You are saying every answer must answer the original question. That is crazy. It results in redundant answers and no added value. Usually people like you add further conditions like "straight up as asked" no matter how crazy or XY the question is. Here, we want answers that are helpful and we would rather an answer complement another answer than replicate it. It's not fine, you made my answer and our collection of answers worse.
    – Harper - Reinstate Monica
    Dec 5, 2017 at 19:00
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    The real problem with nicks is not localised heating, it's that that they concentrate mechanical stresses making it far more likely for the wire to snap.
    – Peter Green
    Dec 5, 2017 at 20:09
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    @CortAmmon you and Sam are both setting up a straw-man, where the damage to the wire is insubstantial. For instance Cort, I never said "reasonably small scratch mark". I didn't claim it, so I don't need to prove it. Sam, on the other hand, has claimed that 19% wire damage for 0.3mm will not cause heating. THAT is a bold claim, bold proofs are called for.
    – Harper - Reinstate Monica
    Dec 6, 2017 at 1:41
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    When I didn't have a stripper, I would roll the wire along the edge of a razor blade and then pull that piece of insulation off with fingers.
    – WGroleau
    Dec 6, 2017 at 3:16
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It depends on the frequency. If you nick a wire carrying 60 Hz, no problem. Nick one carrying 10 GHz you've got a big problem.

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    @HankyPanky These sort of frequencies can come into play on standard network cables. I have manually made CAT7 network cables for 40 Gb/s connections. These operate at frequencies (the higher harmonics at least) well in the 10 GHz range. 5 GHZ is also nothing special on coax cables used to connect an antenna to a Wifi access-point.
    – Tonny
    Dec 6, 2017 at 11:58
  • @HankyPanky yes, certainly, with hand-tools. You don't get nicks in unfortunate places assembling the connectors though. You just cut the insulated cores to the right length, pop them in the right places, and then crimp on the insulation-displacement connector (or with some sockets, push them into Krone IDC receptacles). 10GBase-T is not 10GHz on the wires: there's some clever multi-voltage-level encoding for multiple bits per clock, and two pairs to transmit in parallel. Caveat: I've never yet had to make a 10GBase-T cable.
    – nigel222
    Dec 6, 2017 at 14:12
  • Stress concentrators, work hardening effects etc can cause you grief in DC wiring just as well.
    – rackandboneman
    Dec 6, 2017 at 16:02
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    @Tonny Isn't cat 7 rated for like 600 mhz?
    – user9248
    Dec 7, 2017 at 2:30
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    @Tonny, To my knowledge, there are no or very few transistors that have a gain bandwidth product above ~6GHz, so I highly doubt that you are working on cables that carry 10GHz signals directly.
    – Sam
    Dec 8, 2017 at 16:35
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Since it isn't clearly specified what the wire will be used for, i will enumerate a few scenarios when copper wires are used, and analyse the impact of the scratches in each case.

a) carry electricity (for the purpose of powering an electrical device)

b) carry electrical signal (which is the same as carrying electricity, but this time, either the intensity/voltage/frequency of the current vary in time, as to encode some digital/analogue signal)

c) generate magnetic field

d) generate heat

e) generate light

Analysis of the impact:

a) as long as there is physical contact between the wire and the next metal part in the circuit, electricity will flow. Scratches do not affect conductivity (this aspect has been previously mentioned in Jeffrey Boettger's answer). The fact that the current will flow is not even influenced by the contact surface between the two metal parts - so scratches don't have the least influence

c) this is the case when the wire is used to make a coil, which is a component widely used in electronics (load speakers are just an example where we use coils). This time, scratches will affect the magnetic field, making in irregular. If the coil has many turns, scratches over a short segment might not be critical, but, from a theoretical point of view, every geometrical irregularity of the wire will affect the magnetic field.

b) this is the case when the wire is used for internet/television/telephone. As i mentioned above, the signal is encoded as variations in the current's voltage/intensity/frequency. None are influenced by scratches in the wire. However, in telecommunications, it is often the case that a pair of cables are twisted together, for the purpose of cancelling each other's magnetic field. That's because magnetic field represents an interference that affects the signal. As i stated at point c) above, if the wire has any irregularities, its magnetic field will not be uniform, meaning that it can affect the neighboring wire's signal.

d) this is the case when the wire is used in electrical heaters. The heat property is only influenced by the current intensity. Scratches will not affect that

e) this is the case when the wire is used for a light bulb. Light, just the same as heat, is only influenced by the current's intensity

Considering the photo provided in the question, i am aware this wire will not be used for either heating or lighting. I just thought it was worth mentioning points d)and e) along with the other points.

There is also a mechanical aspect involved - how resistant will be the wire to repeated bending. Scratches can be of two types: longitudinal (along the wire) or transverse (across the wire). Bending has the potential to enlarge transverse scratches, but it will not influence longitudinal scratches. (This aspect has also been mentioned in a comment by Hot Licks).

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    Just a small nitpick: Why would you define an arbitrary ordering for your bullet points, then discuss them in an alternate order? If you wanted to discuss point c before point b, then you should have called it b.
    – Tim Seguine
    Dec 9, 2017 at 11:06
  • i thought someone would notice that; from a logical point of view, point b comes after point a, because it's a particular case of it. however, when i detailed the explanation, i needed to use at point b something from point c, that's why i chose to discuss point c before point b
    – Newton fan 01
    Dec 11, 2017 at 8:52
  • That much of your intent was clear from the text. What I am really saying is that it is unnecessarily confusing to read. In terms of electrodynamics, an electric field is in no way more fundamental than a magnetic field, so you could have just as easily put point c first, and kept the ordering linear, logical, and consistent. I consider it a loss, because this contains relevant information that the accepted answer lacks.
    – Tim Seguine
    Dec 17, 2017 at 15:01
  • My opinion here is different. I do regard the electric field as more fundamental, perhaps because of the order i have studied these subjects in school (the physics curricula in my country introduces the magnetic field 3 or 4 years after the electric field). I specifically put the electric field before the magnetic field. However, i must agree that for a professional physicist these topics are equally difficult; moreover, they are strongly correlated. But the average individual has higher chances of having heard about the electric field, and not about the magnetic field
    – Newton fan 01
    Dec 18, 2017 at 9:11
  • You essentially counted 1, 2, 3, 4, 5, then immediately counted 1, 3, 2, 4, 5. That is confusing. Period. My concern is completely editorial. By countering my suggestion for an alternative way of ordering it, all you did is demonstrate you are missing the point.
    – Tim Seguine
    Dec 19, 2017 at 17:38
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Small scratches should not affect conductivity of the copper wire at all. This is common when stripping wires bare with knives, side cutters and other misc tools. When one is preparing copper wire they should get into the habit of using wire strippersthis particular tool strips wire to gauge minimizing damage.

Don't be to worried about little nicks and scratches. Just be mindful of the plastic coating. Exposed wire could be a potential shock or fire hazard.

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Like @RedGrittyBrick already mentioned, if it's superficial surface markings, then no worries, they're only markings. Use a flashlight and magnifying glass, so you can try see to see if you would call them surface markings vs. a real nick. If you see something you'd call a "nick", then just redo the stripping.

I only occasionally do electrical work, but have broken wires at the insulation just by moving them slightly in the box. Since it's after the fact, I can only guess it was due to nicks. And if so, no way to measure how deep the nick was before the break. So better safe than sorry.

Also like @Harper says, make sure you have good wire strippers. Try about a dozen times on some extra wire, if you are not getting the hang of it, then maybe you should consider the tool then. If it's the red cutter tool with screw, make sure that the screw has been set properly for 14 gauge. If it's the yellow tool with multiple positions, then make sure a) you're actually doing 14 gauge wire and b) the wire is going into the 14 gauge position and not its 16 gauge neighbor. It is possible to strip with the 16 gauge position but will usually lead to bad results.

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