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What's Wrong With This Picture III

Discussion in 'Question of the Day' started by ship, Dec 13, 2004.

  1. ship

    ship Senior Team Emeritus Premium Member

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    Here's the next problem photo. The picture on the right was found within a Soco type multi-cable plug. What caused the little nicks in the insulation with the broken strands of wire coming out?

    Don't worry about the photo on the Left it's there just for awe factor in having rubbed against something sharp and careless tech people in not having noticed.

    [​IMG]
     
  2. Radman

    Radman Well-Known Member

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    There is missing insulation on the wires ;)
     
  3. JahJahwarrior

    JahJahwarrior Active Member

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    knife? I know sometimes at my youth group we ziptie extension cables to the battens, and everyonce in a while someone gets careless with teh boxcutter when removing the zipties, and slicees through the outer jacket, sometimes in to the wire insulation too.

    and um, Ship, the side that is just there for it's awesomeness, isn't that on the [Ship knows left from right because he is awesome]. :eek:
     
  4. ship

    ship Senior Team Emeritus Premium Member

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    Remember, or perhaps I should have mentioned that this section of the cable with 3" of the outer jacket removed was under a Socapex type multi-pin type of plug plug. You will note by the photo that now 4" worth of cable is exposed out side of the jacket.

    When I took the cable apart, I noted that the strain relief on the plug was not holding tight to the cable.

    Last hint, I'm not going to answer until Mayhem in already knowing the answer answers this time or tells me to. No more hints either.
     
  5. JahJahwarrior

    JahJahwarrior Active Member

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    one more thought, just since I didn't really want to edit my post again :) you said that the wires there were IN the plug? then it couldn't have been a knife or something. But, could it have been a cable under stress, which pushed the wires against a strain relief, or jsut a part inside the plug? that would damage some, but probably not all of the wires, and it doesn't look ilke they are all slit like that.
     
  6. SuperCow

    SuperCow Active Member

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    Friction? Could it have gotten tangled and dragged, thereby going through that portion of the insulation?
     
  7. JahJahwarrior

    JahJahwarrior Active Member

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    ha! Ship, you must have posted as I was typing, and i didn't bother to return to my message. Yes, I did note you said it was under a plug, and i was typing that as you were reminding me of it.

    Heres my guess: the spot where the insulation is cut is probably, if you look, at a point on the plug (I am not familiar with their design, a socapex, but I have a genreal idea,) where the strain relief starts. The cable was hung or something, and the insulation was moved a whole inch toward the other end, the cable stretched or something. Insulation can slide, I know, because i have had it slide on me alot of times when stripping small cables. So boom, there is a strain on the cable for a long time and the insulation on the outside of all the cables moves downa n inch. Now, instead of the nice thick insulation being held in by the strain relief, the cables (individualones) are resting on it, possibly being bent instead of having that nice curve to the that the strain relief makes possible. Because they are being pulled on, and are resting on the strain relief, they get sliced into by the strain relief by gravity.

    um, ,that appears to me to be the asnswer. I have observed slightly similar things, just not all at once. (I have observed insulation sliding on cables, and I have observed insulation on individual cables being sliced on cables where they are pulled really tight at a sharp angle)
     
  8. Peter

    Peter Well-Known Member

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    Ship: Did you mean the cable on the left is for awe factor? (I only see one pic)

    As far as the cable on the right, I am thinking, Like those who posted above, that a knife, or at least something quite sharp is to blame.

    The thing that comes to mind, althought it may be way out in left field, is if the insulation was old, dried and cracking, and the cable was bent arround too tight of a corner, causing the insulation to crack and bits of the wire to be pinched outward when the bend was undone. Although this strikes me as rather unlikely.

    Now the question is, is the answer to this really the obvious answer?
     
  9. JahJahwarrior

    JahJahwarrior Active Member

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    yeah, he means the cable on the rig...i mean left. Yeah, that one :) Ship, exactly what WAS it that cut that cable like that??

    L
     
  10. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Ok - well it really seems like JahJahwarrior was on the right track. However, it was not the strain relief that cut the inner connectors. In fact, Ship gave away a major hint when he said:

     
  11. JahJahwarrior

    JahJahwarrior Active Member

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    am I interpreting Ship wrong? I took it to mean that before, 3 inches of cable were uncovered by the jacket, and now there are 4. I assumed that the extra inch was the jacket sliding back, like I said, and letting the cables bep ulled onto the strain relief/some other sharp edge in the plug.
     
  12. sound_nerd

    sound_nerd Active Member

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    from what i understand, someone cut off that extra inch of outer jacket, and in carelessly doing so, they cut into the seperate strands of wire as well. I've seen this happen many times when jackets are removed either too fast, or too careless.
     
  13. JahJahwarrior

    JahJahwarrior Active Member

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    well, I don't thnk that too likely, look at the jacket, see that part with the little like indented curve thingy? about an inch back, it does that, then it angles away. ALOT of the jacket must have been under the socapex plug for it to have the wierd indention/angle thingy that far back. Ship? someone? that's how it seems to me but i have been wrong before :) Lots before! ;)
     
  14. Radman

    Radman Well-Known Member

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    :(
     
  15. soundman

    soundman Well-Known Member

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    looks like it got hlaf throwen into a cable trunk then some on threw another case on it.
    Or did some one spin the end sepert from the cable and the strain was too tight, kind of like a 'snake bite'
     
  16. Mayhem

    Mayhem Senior Team Emeritus Premium Member

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    Ok - as I commented yesterday, JahJahWarrior was on the right track and since that message, Sound_nerd identified the source of those cuts in the insulation of the individual strands, but did put the two together.

    So here is what happened:

    When you look at the picture, the cuts on the inner connectors are about 3/4 of the way up the cable. This places the cuts at the original location of where the outer jacket was removed, indicating that they occured when this particular cable was constructed (hence Ship saying 3" removed when making the cable but now 4" exposed).

    The person who made the cable used a knife to cut the jacket to remove it. In doing so he/she dug the blade in a little too far and cut into the insulation on some (not all) of the inner connectors.

    Once the cable was placed under strain and the strain relief failed, not only did the outer jacket retract, the insulation on the inner conductors was also stretched. Where the insulation was cut, the strands have started to break and if you look carefully, you can see some broken strands of copper wire.

    This obviously presents a fire hazard as given the proximity of the bare wires and/or some moisture either through humidity or condensation or even fluid spill/submersion then you are going to get a nice little lighting show within the plug.

    Not all that familiar with the plug, so I cannot really comment upon the risk of electrocution.

    So - well done - you pretty much covered it all in your various posts.
     
  17. Cat

    Cat Member

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    hmmm

    It appears to me that it was a careless cut as my personal expeariance that it takes a large amout of friction to slice through the jacket then through the coating on the wire to expose them. Unless of course the wires were dry rotted. The rubber making up the jacket is made to withstand the heat and power going through the wires a large quantities so melting is out of the question and the only way friction would work is if there was a sharp edge pressing in at a certin angle. Again this would have to be quite sharp and a very heavy pressure. Also the cuts would only be on one side. Since 3 in of wire were exposed and 4 in are now something must have removed the jacket. After this train of thought I came to the idea that it would have to be a cut. Prob that of a razor blade being that only a few wires were cut open and if you press point down with a razor blade you will slice both the jacket and the coating. A wire stripper may have also done it but from the random wires cut a razor blade seems more likely. If its not I would really like to know what did it. :)
     
  18. ship

    ship Senior Team Emeritus Premium Member

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    The inner conductors were nicked by the utility knife as it was used to cut the outer jacket. Even if only slightly nicked, once the cable was pulled and the strain relief was not sufficient to prevent the outer jacket and really any rubber or plastic coatings over the copper that won’t stretch or un-twist in becoming longer as much from shrinking, the nicks on the conductors than in being pulled split.

    You will also note that this person in being less observant yet had nicked and cut into inner conductors thus the strands coming out of the cuts in the wires after stretching. This stripping of the wire was more than just a nick into the insulation, they cut all the way down and cut into conductors. Than were either less observant than required or too lazy to note they screwed up and not re-strip the wire once the conductors were cut.

    I know who did it and ought to send it out to him and all other similar "old school" crew chiefs of his ilk in an effort to stop their "repair" of cable practices they learned why back when when this specific cable was produced. Such things as this are not all that common for me to see it would seem. Not that re-eduction would do any good.

    As Mayhem says, it’s quite the shorting or fire risk and if even nicked, still proposes a major problem later on.

    Never but never use a utility knife to strip wire with. Tell the old timers that say they know what they are doing that they are being idiots. Nobody has that true of a control over how deep they are cutting into the outer jacket of a wire. Instead, use the nature of a cable’s jacket to it’s advantage in stripping outer jackets. You will note that once nicked, a conductor once stretched splits along it’s length will tend to separate perpendicular to the wire and all around the insulation.

    Now what if instead of using a knife blade, you were to grab the outer jacket with a pair of sharp Dikes - diagonal side cutting pliers in kind of squeezing but also pulling the outer jacket away from the inner conductors while you cut? You kind of rock or piviot the blade off the direct cut onto the jacket while the outer jacket is still pressed into the jaws of the dikes and cutting. Grab the wire, start cutting, pivot off while pulling the outer jacket away from the inner conductors and complete cutting. Grab a fresh section and do the same. Than flex the wire in a tight bend at your cut and the outer jacket will start to split in the direction of the slit you induced into it. Given it often will have some remaining segments of outer jacket that were not cut away enough to finish splitting off cleanily, simply touch the sharp but not knife sharp point of the dikes to the area you are folding and it's amazing how fast even it's tip will caused that stretched section of outer jacket to cut.

    In having the outer jacket stretched and pulled away from the inner conductors as you cut, you are than safe from nicking the inner conductors because they won’t be in the area of the cut. Otherwise in the case of a thermoplastic outer coating which does not stretch as easily such as in this case, you use the dikes to cut into as you are rotating the dikes off the cable so as to not go as deep in more scoring the jacket than cutting all of the way thru it. The intent is a few of these similar cuts into the circumference of the cable as it stretches when you bend it or in not going too deep - you nick the outer jacket and outer jacket only, than to bend the cable at these scored points so it by flexing and thus pulling, cuts around the nicks you induced into it.

    Works on 12/3 SO or in this case 1.5mmx18 conductor Oleflex cable. Nick the wire with the dikes, then bend the cable and let the jacket finish cutting it’s way thru the jacket.

    Sometimes with this practice you will especially on thermoplastic wire nick the conductor still. This will often be the case with SJT cord whips where the outer jacket is completely molded around the inner jacket.

    No matter what method you use to strip the wire, you always want to flex that cable in the area you stripped - either by way of the above in observing the inner conductors as you flex the cable to tear away the outer jacket or by way of flexing as a means of inspection after the utility knife cut into it which is very hard to control the depth of even for an expert. In any case, but observing and looking for these nicks into the inner conductors, you than will be able to prevent problems like this nine years after the Soco type plug was installed on the cable. Luckily I noted the failed strain relief in repairing it’s problem, otherwise, this cable very well could have caused a large short in conductors arcing. Much better to cut the cable and start over than to have a fire risk in your grid even if you make a mistake in nicking the insulation of a single conductor. I use dikes in stripping my cables. 98% of the time it’s the best method and does not nick the outer conductor. Those using a knife to strip off an outer jacket 50% of the time at very best won’t nick the inner conductors, but 50% of time will nick the jacket of them if just by some. Most “electricians” will live with just a nick in the conductor insulation. This photo shows what happens once the cable stretches out to those nicks in the wires.

    There is better ways to strip the outer insulation off a cable.
     

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