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I am having a trench dug that passes through our asphalt driveway (previously a public county road). I am running power to a pump house on the far side and want to run two water lines and sprinkler wire back to the main power side. The feeder wires to the pump house will be run in conduit. Water and power lines will be separated horizontally in the 12" wide, 30" deep trench. The sprinkler cable is rated for direct burial. Is the conduit for the feeders sufficient to meet code for separation between the 600-volt-rated feeders and the 30-volt-rated sprinkler cable or does the low voltage cable have to be run in its own separate conduit? I know sprinkler wire doesn't have to be that deep, but it seems like vertical layering in the same trench could make future repairs more complicated. Plus, I want them deeper so they are not damaged by repairing the driveway.

If I put the sprinkler wire in conduit just under the driveway portion of the trench, do I just leave the conduit ends open?

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Toss one or two 4" sleeves in there (SDR-35 sewer, SCH40 PVC, ABS, etc) and extend them a few feet beyond both sides of the asphalt. They're much cheaper than excavating and repairing the asphalt ever again if another crossing is needed!

Some municipal water utilities require separation between water and other utilities, including electrical, as a matter of policy. I haven't been able to find any national-level building or electrical code (in the US) requiring any specific separation for private lines. Separation won't hurt anything, of course.

If the mains voltage conductors are in conduit then the minimum separation to the low-voltage, whether direct bury or in conduit, is zero (ie none required). I haven't been able to figure out whether any separation would be required if the mains voltage conductors are also direct bury -- maybe it doesn't matter because direct-burying those would have been a short-sighted plan anyway. ;-)

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  • Excellent idea about using a larger, cheaper sleeve under the driveway! I keep trying to think of everything the future might hold and size/type accordingly. Your suggestion allows more flexibilty!
    – cjc
    Aug 31 at 20:52
  • NEC requires a "fixed solid barrier" between different voltage cables in cable trays (indoor, commercial). So, the conduit for the 240V should be sufficient. (Like you, still unsure about if both were direct burial). References to protecting low voltage wires from EMI are mostly from manufacturers (distances of 8-18" separation suggested). There are various soft/stretchy EMI shields that are not very expensive. Planning to just put sprinkler wire on far side of water line unless I hear differently from AHJ.
    – cjc
    Aug 31 at 20:59
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Put the sprinkler wires in conduit the entire distance. By itself, I wouldn't necessarily bother. But you are running conduit for power anyway, so another conduit is not that big a deal. Make the conduit larger than you currently need. Then in the future if you decide to add networking or other low voltage cables you will have it easy.

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  • I failed to mention these are pretty long distances, so I am really trying to keep costs down.
    – cjc
    Aug 31 at 19:41
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As long as you separate electric and water by 12" (which you indicate you plan to) I believe you can share a trench. But you can't (or at least shouldn't!) run high voltage and low voltage in the same conduit. Since you're trenching, it only costs you a little extra conduit here, and since you have so much cover it can be cheap PVC conduit.

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