I am building a pole barn about 200 feet from my house. I would like to run 90amp or so 240VAC to a subpanel, as well as ~400VDC from solar panels, and a pull or perhaps two of Cat5e ethernet cable.

The 240VAC will go to a subpanel in the pole barn, and will be 4 conductor (L1, L2, N and G). The subpanel will also be tied to a ground rod at the pole barn.

The 400VDC will likely be 3 pair, and will go from solar panels to inverters at the house, which tie into an existing grid connected solar system.

The ethernet will have two runs, mostly for redundancy. I only need one. I have considered running more, but a better solution might be to put a POE switch in the barn, and use POE to run cameras.

Each group of lines would run in their own conduit. I will try to keep the ethernet conduit away from the others in the trench.

I am considering using aluminum wire for the 240VAC and the solar, for cost. I would probably want to try to go with copper for the solar, since it would frequently cycle between maximum power and no power more often than the 240VAC.

Is 10" suitable separation for the Cat5e? Any other suggestions?

  • How many amps of solar are we talking? Commented Jan 14, 2021 at 22:33
  • Two 40A pairs at about 400VDC. May split into three pairs.
    – mongo
    Commented Jan 14, 2021 at 22:40
  • 1
    Is there a reason you don't site the inverters at the barn? Hauling 400VDC over the underground conduit poses some...interesting issues. Also, where are you on this planet? Commented Jan 15, 2021 at 0:09
  • Inverters in the barn would complicate the combiner/disconnect for existing solar and wind generation. Losses at 400VDC are less than at 240VAC. I already have longer runs for existing panels. What are the concerns about 400VDC in conduit? I have experienced no issues with existing 10yo system. Help me understand the concerns with DC which would want one to send AC from the barn?
    – mongo
    Commented Jan 15, 2021 at 0:50
  • @mongo -- you'd need to do some jiggery-pokery to accomplish rapid shutdown of the array on the polebarn (at least if you're under NEC jurisdiction -- your posts on Av.SE make me think you might be in Canada?) Commented Jan 15, 2021 at 2:17

1 Answer 1


For networking, use fiber optics, or point-to-point wireless.

By the time you provide adequate lightning suppression (UL497 Primary Protection) on copper ethernet, fiber is likely cheaper, and it's definitely more robust. I've never replaced a fiber for a nearby strike, but it's not uncommon to need to replace surge protectors after a storm.

If there's a clear shot, point to point wireless also works well, and may feel more accessible (fiber is not all that difficult, but it can feel daunting to get started with.)

There's really no advantage to using copper wires .vs. appropriately sized aluminum wires for the other two circuits. A thing you might want to consider would be skipping the DC circuit entirely by putting an inverter at the barn.

  • If you put the inverter at the barn, would there be code issues with putting both AC circuits in one sufficiently large conduit? Commented Jan 15, 2021 at 0:26
  • If it's grid tie inverter, you don't need two circuits for AC. You tie into the grid at the barn for the barn inverter. Bim, Bam, one AC cable, and perhaps a fiber, and you're done. Depending on the cost of each, it might cost less to have an inverter at the barn than to run an extra circuit.
    – Ecnerwal
    Commented Jan 15, 2021 at 0:31
  • Placing the inverters in the barn would necessitate changes with service, combiners and code required shutoffs. Additionally, the losses may be greater transporting 240VAC vs 400VDC. I will double check wires, but last time I ran service Al was nearly a quarter of the cost of copper. For ethernet, wireless will not work, but I will look at fiber. Last time I checked the cost was several hundred. Copper is substantially less as a Cat5e to the building would cost about $8.00.
    – mongo
    Commented Jan 15, 2021 at 0:45
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    A quick looks suggests that UL497 surge protection will add about $140 to your $8. And your $8 sounds suspiciously like a cable not suitable for wet locations, which will come back to bite you if that's the case.
    – Ecnerwal
    Commented Jan 15, 2021 at 0:54
  • 1
    All outdoor conduit IS WET. It's DEFINED as wet, and it lives up to that definition.
    – Ecnerwal
    Commented Jan 18, 2021 at 0:25

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