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Underground Wire Short

underground wire short

Underground Wire Short | Here's the section of wire that caused my problem. You can see how the dead short caused a small fire underground burning away the plastic wire insulation. Underground wire, in my opinion, should be placed in conduit. That said, read what Mike Cyr, one of my newsletter subscribers, sent to me below. Copyright 2019 Tim Carter

Underground Wire Short - Conduit and Sand Are the Answers

I didn't build the house I'm living in. Each month I discover something new where the builder and his subcontractors took a shortcut.

A few months ago I had an underground wire short. This wire extends from the corner of my house up to the base of an oak tree. From there it split off to a spotlight and then to a post lamp at the end of the driveway.

Was the Wire Rated For Underground Burial?

Yes, the wire was rated for direct burial.

Was the Wire Put in Conduit to Protect It?

There was one piece of 3/4-inch PVC conduit that ran under the blacktop driveway. On either side of the conduit, the wire was buried in the rocky soil without a conduit.

What Caused the Underground Wire Short?

Frost movement in my soil caused the wire short. It's important to realize I live in New Hampshire and the ground freezes each winter. It then thaws in the spring.

The freezing and thawing cause movement in the soil. Water in the soil expands by 9 percent in volume when it turns to ice. This movement wore away the insulation on the wire where it exited the end of a piece of PVC conduit.

Would the Short Have Happened if the Wire was in Conduit?

Maybe. In my case, you can see in the photo below what was the primary cause of the short. The wire exited the conduit and made a sharp 90-degree bend. That bend in the wire contributed the friction along the edge of the conduit.

underground wire short

The conduit is at the top of the photo. You can see the original underground gray wire in the trench. Look at the closeup photo below to see the wire make the sharp 90-degree bend. Copyright 2019 Tim Carter

underground wire short

The red arrow points to the exact location of the underground wire short before I pulled the wire out of the ground. May the electrician who put in this wire have black flies around his face for months on end every year. Copyright 2019 Tim Carter

I feel conduit is a great idea because it protects underground wires from gardening shovels and spades.

I cut the wire and made an above-ground splice in a waterproof code-approved junction box. I installed all new wire from this junction box to the oak tree on the other side of the driveway. This wire was placed inside new PVC NEC-approved conduit. I connected my new conduit to that which existed under the driveway.

waterproof electric junction box

Here's where I made the splice connecting a new underground cable to the old buried one. The conduit on the left travels up under the drive to the oak tree. The conduit on the right has the original wire that extends back to the corner of the garage. Copyright 2019 Tim Carter

Is There Another Way to Prevent an Underground Wire Short?

Mike Cyr is one of my newsletter subscribers. He's a great man that I hope to meet one day. He routinely responds to my comments in my newsletter and had this to say when I bemoaned my shorted wire in the spring of 2019:

"I have a friend who just retired as a master electrician and has done a lot of my work and we have buried some wires underground over the years.

He is against burying wire in conduit, and his reasoning is this: He claims that frost up here in northern Maine can go deep and can bring rocks up out of the ground and lift and stretch the conduit and actually break a joint or splice in the conduit, thus breaking the wire or opening a small gap in the conduit enough to fill with water and freeze the next freeze-thaw cycle and break the wire.
When he and I buried wire many times and many years ago, he would use direct burial wire which is designed for underground and we would put about 1-2 feet of sand under the wire and then make the trench 1 to 2 ft. wide and zig-zag the wire in the trench thus allowing the wire some slack to move with the frost.  We would then bury it with sand or crusher dust.
He told me he has never had a wire break doing it this way but has had many come apart in the conduits. This is just some food for thought."

Mike's electrician friend is right. Frost does push rocks up through the soil. Just ask any New England farmer! I don't dispute anything Mike's electrician said and protecting the wire with lots of sand is an excellent idea.

If you're going to bury your wire the way Mike's electrician does it and you're passing through a garden area, be sure to bury the wire quite deep so no shovel, spade, or roto-tiller can cut the wire.

What Does Wire Buried in Conduit Look Like?

It looks like victory. Can you see how this would prevent the wire from rubbing against anything? Sure, in extreme conditions as described by Mike you could get a failure. But if you live where the soil doesn't freeze, the conduit is the only way to go.

underground wire short

This is 3/4-inch PVC electrical conduit. The 90-degree fitting at the tree will connect to an additional piece of conduit that extends up into a new 4x4 waterproof box. The conduit is in a shallow trench about 6 inches deep. Be sure to follow the National Electric Code when installing yours. Note that local inspectors can modify some codes. Copyright 2019 Tim Carter


23 Responses to Underground Wire Short

  1. There's just one problem with that photo: Running conduit up the tree! We tried this at my place to mount a driveway light and within a few years the screws were pulling out and the mounting parts breaking. The tree was growing and twisting!

    I ultimately put in a freestanding pole designed for direct burial in dirt (no concrete required). We're working on getting vines to grow up the pole so it looks more natural.

  2. Would galvanized steel conduit fare better or worse, taking into consideration the risk of long term corrosion? What about flexible aluminum conduit?

    • I'm not a fan of galvanized conduit underground. What do you seem to have against PVC? What did you discover when you asked this question on eletrical forums where these topics are discussed? Go do that and come back with your findings.

    • This photo was taken BEFORE the job was complete. There's a new 4x4 waterproof box in place of the one you see in the photo. A piece of conduit extends from the upturned 90 into the bottom of the new box.

  3. hello tim, i found bx cable in my backyard!!!!!!!!!!!!
    from the house to the offset garage!!!!!!!!!! nice huh!!!!! ty, jay

  4. Hi Tim,
    If I’m not mistaken, in our area of Ontario, I have been told that the code dictates that the wire needs to be 18” deep if it is in conduit and 24” deep if it is just direct burial wire. It has to be in a need of sand and have a red plastic caution tape laid over the sand before you backfill with dirt. Is our electrical code here a little better than the NEC down there?
    Oshawa, Ontario, Canada

  5. The last time I buried wire in Central New Jersey they required underground wiring to be a minimum 18 inches deep

  6. Tim,
    I read all of your newsletters and really appreciate all of your knowledge, ideas and tips.
    Thanks, Ernie

  7. Some years ago, I had to move water service from the water pump, involving cutting into an 1/2" water pipe, white in color. 'Magine my surprise when the pipe content was some 12/2 electrical wire. Lucky for me that it was not energized. Take NOTHING for granted in working around previously installed pipes/conduit!

  8. Conduit buried only 6” deep! No wonder you have problems. I would put it in conduit but would bury it at least 12 to 18 inches deep. I’m not a ME but I’m no dummy either.

    • Al,

      Are you sitting down? The ORIGINAL builder and/or his electrician is the one who buried the UG wire only 6 inches deep. The only conduit was under the blacktop.

      That wire looked perfect along the entire length except where it exited the east end of the conduit and made the sharp 90-degree bend. In other words, for the past 19 years the shallow burial posed no issues - unless someone started to dig.

      As we all know, before you ever dig, you're supposed to check for all underground utilities to prevent cutting a line of any type.

      I said down at the bottom of the column that you should follow the NEC - or whatever the LOCAL inspector says is fine.

      I took the time to put the new wire in a conduit the entire way and did just put it back in the 6-inch-deep trench. You'll have to work damn hard to sever the new wire.

      Would it be better to have it 18 or 24 inches deep? Sure, but then even a backhoe operator would grab it and cut it unless they followed the above advice and had all underground utilities marked and the depth verified.

  9. Tim:
    Recently we installed 18 solar panels on top of my 4 car garage, which is separated from the house by an encircling driveway about 20 feet wide.
    We were going to bury the service line from the garage to the house at about the same time that I needed to replace the old blacktop. I was able to get the contractors to time it so the wiring could be laid in a trench from the garage to the house. At that time, I removed the overhead wiring which supplied the original electric service to the garage, & had that placed in the trench as well.
    The final trick was to take & add an "additional" run of "PVC" to the mix, which I then used to run a garden hose thru, from the house to the back yard garden.
    Once everything was in place the paving contractor filled it all in prior to repaving the driveway. Lucky timing for once!

  10. Hi Tim - could you address how you made the wire splice? I’ve had to do two of them here at my home. Both instances included direct burial cable (one was three separate strands and the other was A 4-wire Romex product, if you will). The 3-strand was spliced individually (both mechanical and heat shrink) and thrown back in the hole. The other was spliced with wire connectors and coated with some magic goop. That whole mess was then placed into a buried sprinkler valve box that would allow access to the splice in the future. Just wonder how you did yours.

    • Simple. See the giant piece of granite in the second photo showing the old wire in the trench?

      I cut the wire about 4 inches from where it was exiting the conduit and then put in an above-ground PVC junction box on the vertical granite face. I put the new wire headed to the oak tree in conduit that connected to the box and extended conduit down out of the box for the old wire to be in as it traveled back to the house. Finding the conduit, and exposing the trench for the new conduit represented 85% of the total work on the job. Making the splice was no different than making any joint up with twisting the wires and using excellent wire nuts with wings on them.

  11. you could have had the situation I had when I moved into my house. The previous owner ran wire from the house to the storage barn. When it came out of the house it was in conduit. When it got to the storage barn it came out of the ground in conduit. The thing is it was regular 12-2 with ground romex cable and it was buried less than 2 inches deep in the yard. I replaced it with a run in conduit. I pulled the old wire out of the ground by hand with no effort. If someone had hit it with a shovel.....

  12. Is it code to have the wires spliced in the underground conduit? I ask because I know that within a residence, splices need to be accessible and within an approved box. Thanks!

      • Sounds good. I see that you provided more detail about the splice in reply to a different comment. I asked my question because not much was mentioned about the splice in the article itself. Great work.

  13. Tim - I enjoyed your article on why conduit should be used for buried cable and would like to add my story. Where we live in rural southwest Virginia and our internet access is wireless via line of sight to the transmission tower. Due to where the house is located, the antenna is 400 feet away from the house to "see" the tower. This spring a lighting strike took out the antenna, the POE signal booster and the data cable between the signal booster and the antenna. The repair went very quickly because I had insisted that the direct burial data cable be placed in conduit during the installation. The old cable was used to pull the new cable through the conduit, the new antenna and POE signal booster were installed, and we were back up and running without having to trench and bury a new data cable. The moral of the story is that conduit is your friend and is worth the incremental expense during an installation.

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