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.