Ask the Builder: Burying cable? It’s best to run it through conduit

Q. Tim, what are your thoughts on burying electric and cable TV lines? I can buy approved cable and wire that’s rated for direct burial, saving the cost of installing it in conduit. What’s been your experience with underground utilities like this? What would you do and why? – Glenn A., Columbia, S.C.

A. These questions are excellent. These issues come up for a lot of homeowners, even if it’s just a simple project of adding a new post lamp out on a back patio.

I didn’t build the home I currently live in. It has lots of underground buried cable. Last spring all of a sudden one of my circuit breakers started tripping, indicating a dead short. Had I been testing the electric monitoring system I’m now using, I would have been alerted to the dangerous arcing weeks before the breaker started tripping. But that’s a story for another day.

I traced the cause of the dead short to a small place where a buried cable passed through a plastic conduit that was installed under my driveway. The cable was rated for direct burial, but the annual frost heave in the soil here in New Hampshire had caused the cable to rub on the sharp cut edge at the end of the conduit. Eventually the up and down movement severed the insulation and the bare wires shorted out in the soil.

Had the cable been buried in conduit all the way from the house up to the post lamp at the end of my drive, I would not have had to waste a day replacing the cable and installing 70 feet of new conduit. I was shaking my head the entire time digging the new trench. How could the electrician or builder think saving $30 was a good idea? That’s all the conduit would have cost when the house was built.

I’m a huge fan of putting all underground cables and wires inside conduit. I’m an even bigger fan of putting these in trenches deeper than the National Electrical Code minimum depth. Take this one step further, I’m a monster fan of taking photos of the open trenches after the conduit is installed and visible. Shoot photos from many angles showing future homeowners where the conduits and cables are buried. I print out these photos, put them in a waterproof plastic bag and tape the bag to the electric panel for safekeeping.

If you’re not a fan of using conduit, you may change your mind when that gardener in your family pierces a buried cable while digging a hole for that new bush or tree. With that in mind, it’s a really good idea to think about where landscaping might be in your yard. You may want to route underground cables and wires away from these digging zones of death. I’ve seen aggressive diggers cut through conduit thinking they were chopping a rock or a root.