Not A Stone In The Backfill

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George Stolz

George Stolz

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Location
Windsor, CO NEC: 2017
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Hospital Master Electrician
Had an odd call today. Awhile back, I traced an underground fault on a #2 URD run from a POCO pedestal to a HOA panelboard. At the time, the pro lem was 60V at the panel. One leg had been abandoned in the past, and the two breakers in use were moved to the same leg. The previously abandoned leg could not be located, and I gave up on it entirely, and won't return to it.

I located a fault in the partially damaged leg, and the hole was finally dug this morning.

The conductors were corroded clear through, one phase and the neutral, about a foot apart from each other. One conductor was corroded along it's length for a foot, the other had a focused area of corrosion that went all the way through.

I know this may sound like a stupid question, but what caused this? This cable was probably between five and ten years old, tops.

After the repair, I still read only 106v at the panel (121v at service, 1.5A load) and a quick check with the 1507 showed a resistance to earth of .02 megaohms and a max voltage of 32 VDC.

There are no rocks in the backfill, and I have a hard time believing that a cable could get abused so badly in installation. Thoughts?

I have advised against further locates and digs, and have advised to plan on digging a new trench through the landscaping and installing conduit this go around.
 
Is it possible that area of the damage has a chemical or other corrosive component that is affecting that location of the cable? Is there some feature of the property where it is possible a corrosive component was buried in the past and no one noticed during the installation?

Maybe the cable was stored before or after delivery and some corrosive was spilled on it before installation?


I have seen the coffee some of the guys drink, and if they were to spill that on the cable, I would definitely say that was the cause. ;):)
 
Sometimes, the cables are damaged by rough handling prior to dropping in a trench.

Warehouse gorillas don't care about the insualtion, the deilivery driver drops the coil off the tailgate of the truck, the cubby installing it is only worried about having a brew with his buddies tonight......

....Next thing you know, there's a big gash in the cable. And no one notices it when it get buried.
 
Rough handling before & during installation. Gophers, ground squirrels, mice, rodents of any kind. Pinholes in the insulation at time of mfg. Faults at regular intervals means there was a snag on the spool as the wire was unwound.

We always dig up the bad spot, cut and clean up the ends then meg again before splicing. Depending on the length, after two bad spots it is time for new wire. Even those smallest nicks or bruises need a layer of scotchkote and tape before you cover things back up.
 
I've noticed PoCos seem to be installing conduit more these days than they did when they 1st started going underground decades ago. I think they have discovered the direct burial methodology is not cheaper in the long run.

Me, personally, I'm a conduit guy and will exhaust every ounce of breath discourging the use of direct buried cabling (except maybe UF in a residence).
 
ptonsparky said:
I give a "Taillight Warranty" on direct bury. Most opt for conduit.
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The only thing that gets direct burial around here is coffins. :D

It could have been a manufacturers defect in the cable. No one did anything wrong, just murphy's law. And, you got paid to undo it.

I wonder about those things too, its not just you.
 
As an aside to this discussion, at least a few poco's in my area only allow conduit for service laterals. Ultimately it rests on the ownership of the lateral. If the poco owns the lateral they they install conduit. If the rate payer owns the lateral then they allow DB. :grin:
 
Pierre C Belarge said:
Is it possible that area of the damage has a chemical or other corrosive component that is affecting that location of the cable? Is there some feature of the property where it is possible a corrosive component was buried in the past and no one noticed during the installation?

Maybe the cable was stored before or after delivery and some corrosive was spilled on it before installation?


I have seen the coffee some of the guys drink, and if they were to spill that on the cable, I would definitely say that was the cause. ;):)
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This sounds the most logical. Must be some sort of soil contamination or some really cheap, unlisted conduit.
 
I saw a direct bury 4/0 quad use al fail, it megged a dead short to ground, it was for a 50 hp motor, but was still working. I installed the cable, was inspected, not a rock in the backfill, as it was sand we brought in.
We found it with a cable fault locator, dug it up and the cable jacket was swelled and the AL conductor turned white.
We discussed replacing with conduit and copper, but its a 1/4 mile run and the cost was 20K at the time due to copper costs. It was repaired and has been fine.
Its a mystery why it failed..
 
hardworkingstiff said:
Me, personally, I'm a conduit guy and will exhaust every ounce of breath discourging the use of direct buried cabling (except maybe UF in a residence).
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I don't even like UF cable, seen to much that was damaged. I hate digging so if I have to trench any at all I like to get my money's worth and make sure I don't have to dig it up again.
 
It's hard to figure out why it failed and could be any one of the reasons stated above. I used to help out a local electrician here in town when there would be a problem at the local mobile home park. Seems like everytime it would rain we would be over there trying to get temp service to a coach or coaches until we could locate the fault(s). I was very surprised at how many times we were there.

Thats one of the reasons I'm a conduit guy myself.

Here the POCO runs what they call CIC (cable in conduit) not near as thick as PVC, but does offer some level of protection. On commercial they always require conduit.
 
What all you 'conduit only for me' folks don't think of is all the millions of miles of cable in the ground that still works just fine.

I did some work a few weeks ago on some UF cable installed in the early 60s, and it had a pull string in it to open the sheath. Not only was the cable perfectly fine, but the pulling the string still worked as well.
 
480sparky said:
What all you 'conduit only for me' folks don't think of is all the millions of miles of cable in the ground that still works just fine.

I did some work a few weeks ago on some UF cable installed in the early 60s, and it had a pull string in it to open the sheath. Not only was the cable perfectly fine, but the pulling the string still worked as well.
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When you find yourself digging up a lawn to replace cable under warranty i hope you remember how much you saved.

If you figure in the 6 inches less you need to dig it offsets the cost.

If i have any say in the job it will be in pipe, i simply do not enjoy digging twice
 
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