Underground Wire Short
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.
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.
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.
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.