120v -w/no load, 0v w/load.

[Fred B]

That is poor placement of DB. Too many sharp rocks. I hope you checked for additional faults.

I agree, DB in large crush just seems like its asking for trouble. There was at least one other posible that showed up with the A-frame.

 

[zbang]

Nothing really left of the aluminum wire.

It's nice to guess the right answer (post #2).

 

[ptonsparky]

I agree, DB in large crush just seems like its asking for trouble. There was at least one other posible that showed up with the A-frame.

If it showed up, it is. Maybe not today but soon enough. It will find a pin hole.
While you're digging those up treat every shovel bump or nick as if it is a fault. Paint it with scotchkote or something similar. Or heatshrink it.

 

[GoldDigger]

...
...
It became an annual rite of spring to repair feeds to irrigation pivots. I think the most I ever patched was four breaks in one feed, but not all on the same trip. That was when it became clear that a megger was an essential part of the process.

Keeping in mind that what a megger detects is not an open or high resistance in the conductors themselves but rather a break in the sheath and insulation that causes a high impedance connection to earth and also exposes that part of the wire to corrosion (see Post # 38).

 

[ptonsparky]

The fault and cable locator were one of my favorite toys. Just sold the pair for $700. Beer money for my retirement. Maybe .17 cartridges.

 

[kwired]

Just an update on what I found.

View attachment 2560721 View attachment 2560722 View attachment 2560723
Found with a Greenlee thumper and A frame, and a locator. Was personally amazed at how close it got me to the actual fault location. That wire looks to have gotten damaged during a previous excavation by someone putting in the drainage line that is under the wire. Nothing really left of the aluminum wire. There was a slight tick farther up the cable indicating other possible damage to the conductors. There is some damage to the other conductor in this hole too, but not total failure. Looks like it got hooked by an excavator bucket tooth.
Never seen corrosion this extensive. The opening of the insulation is original, dirt immediately adjacent was full of the corrosion matter.

It is aluminum oxide. See it a lot. If you mishandle conductor during installation and nick it, it can lead to this eventually. Can't really recall ever having copper conductor burn open like that. Maybe small conductor UF cables will eventually burn open but not in similar fashion as aluminum, and usually takes longer for them to become open circuit as well.

If you are in sandy soil sometimes it gets hot enough the sand around it tries to turn into glass, even more so if a lightning strike contributed to the failure.

 

[Fred B]

So the pictures were of a different call, but similar circumstances. This was a service that suddenly lost half the power. Customer regardless of normal diagnostic test still couldn't understand how everything could work fine for years then suddenly after a power outage it would stop working. He had a couple of other guys out and nobody came up with why. Layed out for him the likely scenario but he wanted "proof". Now there is no doubt why there is no power on one leg.

Thanks for everyone's input on the locator and A-frame thumper use for this diagnostic. Without this it would be days of digging to finally find this fault. The guy that works with me is still days later talking about and amazed that this ("black magic" lol) found it without having to dig up the whole yard.

 

[ptonsparky]

So the pictures were of a different call, but similar circumstances. This was a service that suddenly lost half the power. Customer regardless of normal diagnostic test still couldn't understand how everything could work fine for years then suddenly after a power outage it would stop working. He had a couple of other guys out and nobody came up with why. Layed out for him the likely scenario but he wanted "proof". Now there is no doubt why there is no power on one leg.

Thanks for everyone's input on the locator and A-frame thumper use for this diagnostic. Without this it would be days of digging to finally find this fault. The guy that works with me is still days later talking about and amazed that this ("black magic" lol) found it without having to dig up the whole yard.

Like I said, it is a fun tool.
Remember you still need to call in for emergency locates just to CYA.

 

[kwired]

So the pictures were of a different call, but similar circumstances. This was a service that suddenly lost half the power. Customer regardless of normal diagnostic test still couldn't understand how everything could work fine for years then suddenly after a power outage it would stop working. He had a couple of other guys out and nobody came up with why. Layed out for him the likely scenario but he wanted "proof". Now there is no doubt why there is no power on one leg.

Thanks for everyone's input on the locator and A-frame thumper use for this diagnostic. Without this it would be days of digging to finally find this fault. The guy that works with me is still days later talking about and amazed that this ("black magic" lol) found it without having to dig up the whole yard.

As the conductor is consumed, it gets smaller, which makes for more resistance in the "bad spot". when you get down to not so much left and are running significant load through it, it very well may be "glowing" if you could observe it.

If it were still "working" but there was power outage, current stop and it will cool, maybe that sets it up for failure if it rapidly heats up when load suddenly returns? Just a thought. It might not handle multiple motors starting all at once though it had been handling one at a time before the outage?

Even if not for outage that was going to eventually fail at some time soon

 

[Fred B]

? Could this open conductor have been "dumping" enough current into the earth to be measured 1. On the grounding conductor, 2. Measured and create an issue on a inground pool? It seems it should have been detected on either depending on proximity.

What would be a shock potential if you have a grounded tool metal plugged into a grounded receptacle and walking over the shorted conductor? Would voltage be detectable by a meter if connected back to the panel and a probe into the earth?
Seem this could be possible. Also think would be dependent on depth and ground resistance at any given moment. Any way to calculate a worse case scenario at a given depth?

 

[ptonsparky]

? Could this open conductor have been "dumping" enough current into the earth to be measured 1. On the grounding conductor, 2. Measured and create an issue on a inground pool? It seems it should have been detected on either depending on proximity.

What would be a shock potential if you have a grounded tool metal plugged into a grounded receptacle and walking over the shorted conductor? Would voltage be detectable by a meter if connected back to the panel and a probe into the earth?
Seem this could be possible. Also think would be dependent on depth and ground resistance at any given moment. Any way to calculate a worse case scenario at a given depth?

IMO:
1. Yes 2. Yes What should have the detection caused? Pool GFCIs would not operate because they are looking for an imbalance of the circuits to the pool that it monitors.

The closer to the fault the more likely you would feel it. A line fault vs a grounded conductor fault would more likely be measurable, but that is what is done at dairies for stray current issues.

What scenario are you asking about? In the years we did fault locates we never experience any shocks walking above faulted conductors. 480 and down. Note, we were not barefoot. . Usually we did a voltage check at each end, confirmed an issue, and disconnected power.

We've seen anywhere from your picture, which is quite common, on up to glass.

 

[Fred B]

IMO:
1. Yes 2. Yes What should have the detection caused? Pool GFCIs would not operate because they are looking for an imbalance of the circuits to the pool that it monitors.

The closer to the fault the more likely you would feel it. A line fault vs a grounded conductor fault would more likely be measurable, but that is what is done at dairies for stray current issues.

What scenario are you asking about? In the years we did fault locates we never experience any shocks walking above faulted conductors. 480 and down. Note, we were not barefoot. . Usually we did a voltage check at each end, confirmed an issue, and disconnected power.

We've seen anywhere from your picture, which is quite common, on up to glass.

A way to calculate expected voltage at surface of ground for a set available voltage at source. Is there an assumed resistance of earth, wet, dry, soil type, that would say a fault might be at a given depth?

 

[ptonsparky]

A way to calculate expected voltage at surface of ground for a set available voltage at source. Is there an assumed resistance of earth, wet, dry, soil type, that would say a fault might be at a given depth?

I don't think it is possible to assume any of it. Way too many variables. We had no substantial moisture since August of last year and our soil was ground cracking dry clay a month ago. Now, after 4" of good soaking rains all has changed.