Extension Cord Testing

[Tony Wells]

OK smart guys, I need some ideas. I have a couple, but want to see what the group comes up with.

I have a nice, 100 foot long 12-3 conductor extension cord, with a triple tap on the female end. Somewhere in the cable, there is an open in either the neutral or hot conductor, making it useless in the current condition. It's probably near one end or the other, but they are molded and not readily accessible to test. What I am trying to determine is a way to determine where the break is. I don't mind losing some length on the cable, but I am loathe to just whack the ends off and replace the connectors just to see. Especially the triple tap. If I have to, I will put a new male end on, but would rather find out where the break is and fix just that end, if it happens to be near to the end. I may end up losing the triple anyway, but if that's the case, I'll just live with it. Got it free with some other stuff at a garage sale years ago, and just set it aside for the time. I know I can check between the gnd and both the hot and the neutral to see which one it is, but as far as how far down the cable, or which end it is closest to....I can't seem to figure a sure way. Not that I really need it, but I hate having stuff that doesn't work.

Any ideas?

 

[gr8legs]

95% of bad extension cords are bad at one end or the other - so the first test is to plug the cord into a known good outlet and plug a test lamp into the outlet end. Then vigorously flex the cable at each end and see if flexing either end gets the lamp to flash. If it does then you know which end to replace. This may also work for a break in the middle of the cord but takes much longer to locate because you have to massage every 3" section of the cord.

If that doesn't work then get a non-contact voltage sensor and run it from the source end along to the output end until it goes dark. Note that this only works if the break is in the hot lead (you can determine which lead is bad with an ohmmeter), and also note that the conductors in extension cords are spiraled around at about a 5" twist so the tester will flash as you move along the cord.

I have occasionally used a capacitance meter to determine the length of contiguous conductors but the method isn't all that reliable.
Also, if the break is mid-cable then the cord has probably been over-stressed either mechanically or electrically and another failure should be expected.

Good luck!

Stu

 

[RJSakowski]

If you can't find the open at one of the connections, you can always cut the cord in half. One half will be good. Wire a new plug or socket and you're good to go. You can cut the remaining length in half and wire the good half with new connections. You will have 75 ft. of good cord.

 

[RJSakowski]

If that doesn't work then get a non-contact voltage sensor and run it from the source end along to the output end until it goes dark. Note that this only works if the break is in the hot lead (you can determine which lead is bad with an ohmmeter), and also note that the conductors in extension cords are spiraled around at about a 5" twist so the tester will flash as you move along the cord.

Stu

If the break is in the neutral lead, you could temporarily jumper a hot wire to the neutral. The easiest way to do this is to use a duplex outlet and cross wire a power cable to it.

 

[Tony Wells]

Stu, pretty much done that with the shake test for each end, but have not massaged all 100 feet of it. No indication of a break near the ends, as I had hoped.

Also tried the ticker. Even went to 240 volts, since it seemed to be sort of hit or miss along the wire. Not much difference. And yes, knew about the spiral wind in the cord.

One promising idea I had does involve a Z meter. Being as there are 3 supposedly equal length wires in this cable, and they are twisted, they should make some sort of "gimmick" capacitor. The pair with the lowest measured capacitance would include the broken wire. I just am not convinced that there will be a measurable difference if the broken conductor is, for instance, only about 10 feet shorter than the others. If that is the case, however, and I identify a "bad pair", I can check from the other end and the measured value should be substantially lower. Ruling out the wires with lack of continuity is the easy part. I know which one is broken, I just need to know how long each "half" is. In the low voltage world, there are instruments that are designed to locate breaks in network wiring. My brother has an instrument that we use to certify the LAN cabling we run. It gives a length value for each of the 8 conductors in CAT 5 cabling, for example. I'm not positive how it does this, but I believe it bounces a pulse off the end of the conductor and times the return, sort of like radar and sonar. It's amazing how much difference there can be between the 8 conductors over a run of say, 800 feet. And of course, that can be detrimental to traffic over the cable. But I digress. I am thinking that I may get it and check this cord using one of the known conductors and the short one to see how short the machine see it as. I can do this from both ends and see if it all adds up close to the supposed 100 feet. It won't. Even the good conductor will be long, because of the twists, but if one is broken, it should show up as really short. (I hope)

As far as mechanical stress, this cord looks almost new. There is no damage to the jacket that I have found. I have a feeling the break is near the end, but this is also an educational opportunity.

RJ, Yeah, I thought about that too. It may come to that if I can't resolve this wire break issue. Really rather not have to do that. But I will rather than toss it.
It's been a little while since I stretched it out to work on it, but if memory serves, it's the hot that broken, but good point on temp criss-cross wiring on the neutral and the hot.

Good thinking, guys......keep em coming!

 

[cvairwerks]

TDR....Time Domian Reflectometer. We use them to check coax on the airplane when we have problems. Not a cheap instrument at all, and it take some skill to read and interpret the display results.

New 12/3 triples are around 59$ at Amazon, so value your troubleshooting time as appropriate.

 

[Tony Wells]

Oh, I know......but like I said, this is partly a mental exercise and I like a challenge. And it's not the only 100 footer I have. I have 2 or 3 10-3 cords too, but they are home made with a quad box on one end. Versatile and heavy for when they are needed. This is mostly stubbornness lol.

I could always juice it up with a few KV or so and wire up one end shorted, then see if the arc that jumped would blow a hole in the insulation.

Speaking about coax.......I may have a tester that does measure coax length. Not often used, but I may have to dig it out and play with it.

 

[juiceclone]

The non contact volt sensor will work as described above. Get one of those old adapters that lets u plug in either way to test the neutral side. The triple taps, particularly the crowfoot type, are notorious for failing inside the molded rubber body .... possibly bad design or quality...or maybe just an abused life .?

 

[John Hasler]

My brother has an instrument that we use to certify the LAN cabling we run. It gives a length value for each of the 8 conductors in CAT 5 cabling, for example. I'm not positive how it does this, but I believe it bounces a pulse off the end of the conductor and times the return, sort of like radar and sonar. It's amazing how much difference there can be between the 8 conductors over a run of say, 800 feet. And of course, that can be detrimental to traffic over the cable. But I digress. I am thinking that I may get it and check this cord using one of the known conductors and the short one to see how short the machine see it as. I can do this from both ends and see if it all adds up close to the supposed 100 feet. It won't. Even the good conductor will be long, because of the twists, but if one is broken, it should show up as really short. (I hope)

The cord may be so lossy at those frequencies that the tester can't get enough signal back to get a measurement, but it's worth a try.

The tester will be way off as to actual length, but you just need relative measurements. Use it to measure the good pair and write down whatever it claims the length is. Then measure the bad pair and figure out the distance to the break as a percentage. Measure from both ends and average the results.

 

[Tony Wells]

Juice, the ground is fine. I have continuity on it and the hot. The neutral is broken, I just don't know where, exactly. The sniffer/ticker is apparently sensitive enough, and there is inductive coupling in the cable so that it picks up all the way, so that method is out. It doesn't matter which end I apply power to for the test, so apparently both connectors, including the crow's foot triple are ok.

John, yes, I realize there is no real comparison between an extension cord and CAT wiring . I am just hoping to find something that works. I don't know what frequency, or profile the tester uses, but it tests a little above CAT 6 for speed certification. It's one of those little Byte Brothers certifiers. I know it's not going to read correct on really anything, but I am relying on difference in what it "thinks" it sees. Just for curiosity, I may hook it up to a scope and or frequency counter to see what kind of signal is uses. I have noticed one odd thing about it after using it for a few years. A short cable, like a patch cable, takes a LOT longer to cert that say, a thousand foot run. Seems it runs many more iterations for the speed test, or delay, skew....who knows why. And there are different settings for solid vs stranded. None of that should matter for my needs though.