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yarrumretep 04-30-2012 09:14 AM

Workshop sub-panel in barn

I am looking to wire a sub-panel in my barn to support a general workshop. Loads would include standard woodworking tools (including 220V table saw), welding, air compressor, etc.

The house has 200AMP main breaker and minimal in-house loads. Dryer is gas, Oven and cooktop are gas. Water heater is off the oil furnace. I think the biggest single load is the well-pump and/or fridge compressor. We do have sporadic toaster oven, hairdryers etc. Otherwise its just lights, ceiling fans, flat-panel tv, stereo...

We had 4" conduit installed to the barn, so there is plenty of room to pull a big cable. The entire run from the house panel to the barn totals around 155' (probably less, but rounding up)

My questions are:
  1. Can I pull a 100AMP sub-panel from my main house panel as described?
  2. Would 4/0,4/0,4/0,2/0 aluminum service entrance cable be a good choice for this run? Could I do it with something lighter?
  3. Could I put an additional sub-panel in the garage (about halfway to the barn) by interrupting the run? The garage subpanel would have a 220V plug for possible welding and/or electric car charging. Would this require a separate run?
  4. Are there any other considerations I should be thinking about in planning this?

Thanks for any thoughts you can share on this!



itsnotrequired 04-30-2012 10:08 AM

it all depends on the actual equipment loads but with a 200A service and mostly gas appliances, 100A should be no problem. you have a 4" conduit running out there which is going to be big enough to handle anything you want out there.

4/0 aluminum USE is good for 180A at 75 degree C terminations (i presume you have 75 degree c circuit breakers) so you could put a 150A or 175A panel out there if you wanted to. if you only want 100A, #1 aluminum just makes it.

what type of conduit is it? i'm guessing PVC. no problem at all getting the 4/0 in there.

yarrumretep 04-30-2012 01:43 PM

Thanks for the thoughts itsnotrequired. 4" PVC conduit is right. I'd like the possibility of "upgrading" later, so maybe the 4/0 aluminum is good as it gives me a bit of stretch room if I want.

Do you have any thoughts on the additional sub-panel in the garage? Would I think of that as a sub-panel on the garage and then a sub-sub-panel off of that in the barn? Or is it just better to run 2 separate runs - one for the garage and one for the barn?


itsnotrequired 04-30-2012 02:09 PM

not sure of the exact layout of the house, garage and barn but it is permissible to have 'sub-sub' panels. just need to consider that the first sub needs to be sized large enough to carry both subs and that depending on the breakers, you may have coordination issues where a problem on the sub-sub causes the sub breaker to trip but that would be pretty unusual. if it were me, i would run them separate from the main panel.

yarrumretep 04-30-2012 02:18 PM

Thanks for the info, itsnotreq'd. The layout is such that the garage is literally right on the way to the barn. I'm leaning toward separate runs anyway - just to keep things clean-o.

Jim Port 04-30-2012 02:49 PM

You can have sub subpanels, but you can only have one feeder to the building. You cannot have a feeder to each subpanel in the building from another building.

yarrumretep 04-30-2012 03:05 PM

Thanks, Jim. The garage is in the house so in either configuration the barn will have only one feeder.

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