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I’m trying to run power to a well pump house/seed starting shed now, while also planning for a barn/shop several years in the future. I am wondering if I should have two separate circuits (a lot more wire) or daisy chain subpanels. The distance from the main panel to the pump house is 250’ and I don’t want too much voltage drop to the well pump, which needs 230 volts and 30 amps. Overall, expected usage in the building is probably 40 amps. So, originally, I was planning to put in a 60 amp subpanel, running #2 aluminum wires in conduit underground in the same trench as a water line out of the pump house (30” below grade). If I did that right, at 250’ the voltage drop should be under 3% and the pump should get its required 230 volts.

We plan to eventually put in a barn/shop that is about 70’ away from the pump house and would like a 240 volt, 100 amp subpanel there. The total distance from the main to the barn subpanel is somewhere around 275’ to 310’ depending on route and where the panel is in the barn. Assuming expected usage at the barn/shop is around 85 amps or less, and allowing for 5% voltage drop at the farthest branch circuit in the shop, I was planning to use 1/0 aluminum.

Questions:

  1. Does anything seem wrong so far?
  2. Would it be better to run 1/0 wires to a 150 amp subpanel in the pump house and daisy chain to the 100 amp panel in the barn or should I run two separate circuits?
  3. If two separate circuits, should I lay two separate conduit runs, or should I oversize a single conduit run, and later pull 1/0 wires through the same conduit carrying the #2 wires. I am assuming I can T off the single conduit line ahead of where it connects to the pump house subpanel, so I can route the 1/0 wires without entering the first subpanel.
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    It is recommended to go big with sub panels. The cost difference between a 60 amp and a 200 amp is not that much. The feed breaker for the panel/s can be any size at or below the sub panel size, so a 60 amp breaker is good as long as the wire is sized right(larger).
    – crip659
    Aug 25, 2023 at 20:01
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    I would go for separate cables in the same conduit with individaul breakers on the main panel. Aug 25, 2023 at 20:23
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    Would you show a picture of your main panel and its labeling? There may be limits as to the ampacity of breakers it can accommodate, and sometimes high-amp branch breakers are surprisingly expensive or difficult to obtain. It's not just about the wire unfortunately. You may want to make a spreadsheet to find the total costs or conduit, wire, and breakers for separate vs combined feeder.
    – Greg Hill
    Aug 25, 2023 at 21:09
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    You may also want to do a load calculation to ensure you have the overhead to support all the future expected loads.
    – FreeMan
    Aug 25, 2023 at 21:58
  • @GregHill We already have another project of updating our existing main panel. And that will be done way before the barn/shop. Right now we are just trying to get water out of the new well. So the only thing we will be adding before the main upgrade is the 30 amp circuit. But I want to make sure downstream infrastructure is sufficient, economical and easy to work with. A spreadsheet is a good idea. So far rough estimates are kind of a wash...$500 more for wire, $500 less for conduit. Though the larger breaker/1st subpanel probably tips it a couple hundred more for the daisy chain.
    – cjc
    Aug 26, 2023 at 0:47

3 Answers 3

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Daisy chain like a tree, (bigger branch supports smaller branches) not a flower-child (all links the same size)...

If you were planning to use 1/0 AWG [105531 cmils] for the barn alone, and 2AWG [66369 cmils] for the well alone, Using 1/0 for both combined seems not well thought through.

They sum to a bit more conductor cross-sectional area [171,900 cmils] than 3/0 AWG [167800 cmils], suggesting that a bump to at least 2/0 [133072 cmils] would be advisable to maintain the performance you want from the combined/shared service to that point.

Then you can look into how that affects the economics of breakers, sub-panels, alternate wiring schemes, etc.

Note that if you run both circuits in one conduit, but separately, you hit the 80% limitation (from the 90°C rating, assuming as is usual it's 90°C wire insulation) due to more than 4 current carrying conductors sharing the conduit. NEC 310.15(B)(3)(a) but that should not impact your planned use.

However, since plans may change, expensively provisioning now for a barn/shop that may not happen, or may move, is fraught with the potential to spend a lot of money on wire you don't actually use much.

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  • Thank you so much for pointing out my mistake!!! I think I've got it now. If I have less than 4 current carrying conductors I can use the 75C column because these are feeder wires running from main to subpanel with breakers and lugs rated "60C/75C". In the case of two circuits in the same conduit (6 current carrying conductors) I would use 80% of the 90C column, because this is less than the ampacity rating in the 75C column. In my downstream branch circuits (small 15-30 amp conductors) I will be using the 60C column based on NEC 240.4(D) (for <9 conductors in a conduit).
    – cjc
    Aug 28, 2023 at 5:04
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What's best is personal preference. This to me is a personal BTDT, big barn at end of daisy-chained feed that has garage, well, garden shed, RV shed, then barn. I used a single run because it actually gave me more options to deal with power outages. Had rotting poles with overhead feed that I replaced with underground.

None of this might apply to you, my issue is many power outages. Most of the time I just need a couple of hours of a quiet 3200w generator at the house. But extended outages my well needs serious inrush, so at the first outbuilding (garage with multiple freezers) I installed another transfer switch for a 5.5kw that just feeds the daisy chained outbuildings when I need it.

So for me a single feed to the outbuildings works well. After the first building with the second transfer switch I just installed a j-box on the exterior of the building and used the 25' tap rule to feed smaller wire to smaller panels.

This gives me options to run the small generator for just the house, or the big generator at the house, disable the well and freezer circuits, and feed stumble lighting everywhere. When I need big power for extended outage I can isolate the outbuildings feed and run both generators.

If I ran separate feeds to separate buildings my second transfer switch would just be able to feed one building.

This setup also gives me some redundancy, if one generator fails to start I can fire up he second one and have lights anywhere I want them while I figure out why the first isn't working.

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    That is probably the best reason I've heard to daisy chain. Thanks for sharing some very useful ideas! Gives me a lot to think about.
    – cjc
    Aug 28, 2023 at 5:14
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If this is a matter of questions on code compliance then either option should be considered safe and meet any building code. I've seen daisy chained electrical panels before so this should not cause headaches for you, inspectors, or electricians. It's a matter of cost and preference, and those are not the kinds of questions we can answer.

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    I was just hoping to hear people's thoughts so I could maybe consider pros and cons I hadn't thought of running to power to multiple outbuildings.
    – cjc
    Aug 28, 2023 at 5:10

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