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I am looking at replacing a shed on my property with a larger combination shed/greenhouse, and I would like to have the new structure powered. Between the house and the shed, I have a septic drain field that the power line would need to cross. Can I tunnel the power under the drain field without running into any NEC conflicts? Can I tunnel part way, run the conduit along my fence line (which already crosses the drain field) above ground, then tunnel the rest of the way to the new building?

I'm not asking for jurisdictional specific rules - I'll ask the county about that when I file for the necessary permits - I'm just asking about general accepted practices.

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  • 2
    Is there no way to go around the leach field? Yes, it would make the run longer, but impractically so? Commented Jul 23 at 16:31
  • The tank is on the other side of the house, so I have to go under (or over) either the leach field or the line to the leach field. The field extends all the way to the property line; going around with turn a 100 foot run into a 350-plus foot run. Commented Jul 23 at 17:01
  • Another question seems to say it is possible, but I imagine your depth measurements would need to be right. Not deep enough and you might drill/tunnel into the pipes. Commented Jul 23 at 17:09
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    Though unsightly, and requiring additional lightning protection, I'd go for putting a line above ground, on poles. Commented Jul 23 at 19:46
  • Running a self-supporting wire above, maybe adding poles if the distance requires it? Commented Oct 20 at 10:58

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The NEC intentionally doesn't cover other complex systems like residential septic systems due to the huge amount of variance in how they must be designed. So, local jurisdiction requirements notwithstanding, you can tunnel under it so long as you're able to follow the NEC's rules.

I'm no expert on drain fields, but I do know that some of them have a partial gravel backfill. So, in cases like this, you'd need to prioritize the NEC (Rocks are bad, man) over the drain field health unless your local code requirements explicitly say otherwise. Not that I think a few cubic feet of missing gravel is going to hurt anything, just pointing it out as an example.

Beyond the NEC, I personally see no issues with running it under the drain field. The only thing you have to worry about is if either ever needs maintenance that would require digging. So, if you use good conduit, install it correctly, and properly maintain your septic system, you shouldn't ever run into a problem.

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  • the NEC "Rocks are bad"? Yet every new transformer in the neighborhood was recently installed/connected by digging 3 feet, putting in conduit then instead of recovering the ditch with the dirt dug up, rock and gravel was brought in as fill. Commented Oct 20 at 13:53
  • @quill One of the many ambiguous, confounding, and paradoxical practices brought to you by the NFPA lol. Commented Oct 20 at 15:58

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