Guest House tripping breaker

Question

I have a guest house that we use as storage. We have a second bathroom in there which gets used a lot. We’ve never had problems with losing power or tripping the breaker.

A few weeks ago the power to the guest house shut off, it tripped the breaker for the guest house as well as the main house breaker. They have put a new breaker for the guest house but after about 30 minutes of running electricity in the guest house the two breakers trip again. The day the power shut off we had a landscaper cleaning our yard and there was a small portion of the underground feed wire that pokes out of the ground and we think they may have hit it with a weed eater and made a hole, which we did find a hole in the wire.

It has rained for 3 weeks straight which is why we are barely fixing it and the power has been off since then. Would anyone know if because the under ground feed wire has a hole this would cause the problem of tripping both breakers?

Answer 1

Absolutely could be the cause. A hole in the cable could cause an intermittent short depending on rain, rodents, etc. That can draw so much current so fast that it can trip both the feed breaker and the main breaker.

There are rules for how deep wires or cable need to be buried, to avoid these types of problems. Simple cable has to be buried the deepest, with PVC conduit less and rigid metal conduit the least. But sometimes cable is not buried as deeply as it should be, and sometimes what was once deep enough is now near the surface due to landscaping changes over time.

You will likely need to replace the entire cable, but that depends on a number of factors. If so, consider conduit as it costs a little more initially but doesn't need to be buried as deep and is less vulnerable to weed whackers. Plus it allows for future upgrades.

Answer 2

The feeder cable to your guest house is required to be guarded by stout conduit all the way down to 24” burial depth.*

If you can see the wire, then the installation was a hillbilly job from the day it was installed, or has failed catastrophically i.e. by being hit with a dump truck.

The main breaker trip is not a surprise given the critical damage to the wire. The entire feeder needs to be de-energized and disconnected at the breaker, as it is currently a death trap. If someone stepped on it, it could burn their foot off or shock them to death.

For what it's worth, one thing that is NOT a death trap is aluminum wire at large feeder sizes. It is perfectly fine, and can save you a mint on the wire.

Also while it's pricey to buy, Rigid Metal Conduit can be trenched with a garden trowel.

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* + cable thickness, as it is 24" of cover. 18” of cover if conduit the entire way. 6" if the extremely tough Rigid Metal Conduit is used.

Answer 3

I had a landscaper hit the power line to my shed with his trencher (more accurately his assistants). It didn't pop the breaker in the subpanel it runs from, it popped the subpanel breaker in the main panel.

As manassehkatz suggests, I went with conduit and ran new THHN-2 (THWN-2), which you cannot direct bury. THHN is likely going to be cheaper than something serious in the direct bury category (given that it's a whole separate house, you're probably looking at something like SEU at that point) The conduit does a good job protecting the cable from damage. Just be sure to get it buried deep (12" conduit, 18" direct bury).