400A Service from Shop to Home

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bmaclaff

Member
Location
TN
Occupation
Licensed Electrician newby
I am breaking ground on a two story shop building. It will have 400A service via a POCO pad mounted transformer 15 ft from the building. I plan two 200A panels in the shop. I also plan two 200A panels in an adjacent home that will be built in a year. I have seen discussions close to this but not quite. With my newbie experience, I see a couple of options:
1. Meter > 400A fused exterior disconnect > trough, then taps to the two shop 200A interior panels and an exterior tap about 60 feet or so to the home > trough > two 200A exterior disconnects > two interior 200 Panels.
2. Meter > trough > tap to two shop exterior disconnects and exterior tap to house..... (not sure about the disconnects being after the trough and taps though?)
3. Meter lugs x3 to 2 shop disconnects and ext tap to home..... ( not sure about this one either)

Once I get that settled, I'll look at ways to connect generator to the whole system if possible, and solar (not POCO backfeeding).

I'm learning every day and looking forward to your collective wisdom!


FYI, We are operating under 2023 NEC.
 

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Thanks Kasey. One of my objectives is to carry 400A to the house. Around here, if it was a 400A service to house only, there'd be the meter base and two 200a discos next to it, each one covering one of the interior 200A panels. I can certainly do that for the shop, but for the wish to get 400A to the house.
 
If I understand correctly the 400A disconnect is the service disconnect and everything else is a feeder. I don't think the house feeder can be a tap if its 60 feet long but if the disconnect at the shop (service disconnect) is 400a and you run 400A wire to the house and split it to (2) 200A disconnects then it is not a tap and would be fine as the wire is 400 a fed from a 400A disconnect
 
Thanks Eddie. Somehow I thought the house feeder length was ok since it was exterior. Hmmm.

But with your 400A shop disco idea, I'm thinking that would work but I'd need to split from that disco to the house and also to the shop two panels. Is it possible to do a multiple lug from the disco, 1. shop, 2. shop, 3 600kcmil to house. or... 3 and 4 parallel direct bury conductors to house and split them at the house.
 
I feed my home from my shop, I hardly ever go much past a 30 amp 240 Volt single phase load. But then again my heat and hot water are from my shop boilers, my spare fridge and deep freeze are in the shop, and so are my washer and dryer. Plus my stove is on propane.

I know it's nice to have, but do you have any kinds of loads approaching 400 amps in the house?
 
I think option 1 is OK as long as the tap is an outside tap of unlimited length. Could even be 2 taps of 200A wires and not one large 400A tap.

I think option 2 works too and would be cheaper. A 400A disconnect is $$$ compared to two 200A ones. Doing all the splicing on the line side of the disconnects allows you to run 3 wires (per set) to the house instead of 4. You may not even need a trough at the house, just bury 2 pipes from the shop to the house. The main discriminator is whether you want to be able to kill power to the wires running to the house (feeder versus service). Could also be a complication for a generator depending on where you connect it.

Option 3 may not work. Most 400A meter bases come with lugs that allow one large wire or two smaller ones. You want 4 wires per lug, or maybe 3 if one is larger. Hard to put 800A worth of lugs on one designed for 400 unless it is designed to allow different lugs and they have room for all the terminations you want. Same thing with the neutral bar, only so many holes.
 
Joe, the house is fairly large and load calc first pass was 201A and I probably undershot the HVAC. Agree with the fact that concurrent amperage will not be that high.

Suemarkp, yeah, the option 2, going from the meter base directly to a trough, tapping to two 200A disconnects for the shop, and also tapping parallel 4/0 or 250kcmil direct bury to the house. I'm not clear in my mind about the difference between having just 2 separate feeders to the house, each going to their own disconnect and interior panel or actual parallel conductors that are electrically joined at both ends and split out again at the house. I agree with wondering about the concern of having no disconnect for the entire run from the shop trough to the house. Seems like it meets code though, doesn't it?

Thanks to everyone already. please continue to share and help me sharpen my knowledge and plan here.
 
Joe.B, no I haven't. I have a large pad mounted transformer just outside the shop that is at the end of an 800ft run from the pull box at the street. I have no idea what's typical in them, whether it's 3phase to the end user transformer or not. Here, they get a transformer somewhere under 100ft from the end user, but no idea what's in the box. I'll have to look for clues. Here's one thing, the large box at the street I think is just a pull box, large fiberglas (I think) box that stands less than 2 ft tall. The transformer back at my house is more like 4 ft tall.

I don't have any significant 3phase woodworking tool needs, so not sure how it would benefit me.
 
I don't know the answer to this myself, just asking.

Since the house is fed by a feeder do you have to satisfy the "Emergency Disconnect rule". Will the disconnect at the shop be in site of the house?
 
I would use 230.40 ex #3. Meter only, one set of service conductors to shop, another set of service conductors running to house. The 320 sockets we get here do not come with lugs, and we can put on whatever we want, even four conductors per phase would not be a problem. You could also just provide a splice box after the meter to connect everything.
 
Little Bill, we are just out of Chattanooga and the town just adopted 2023.
Thanks, Electrofelon, yeah, 230.40 ex3 sounds workable. then I'd use a couple of 200A disconnects per building, run 4/0 a few feet to the shop panels and then not mess with parallel conductors but run two separate 4/0 or 250's to each of the house panels. What 320 socket do you use?

IF I do solar, it would not be backfed to POCO so with this scenario, I'd need to keep the systems separate per building so they'd be downstream from the disconnect, same with generator I guess.
 
bmaclaff said:
Little Bill, we are just out of Chattanooga and the town just adopted 2023.
Thanks, Electrofelon, yeah, 230.40 ex3 sounds workable. then I'd use a couple of 200A disconnects per building, run 4/0 a few feet to the shop panels and then not mess with parallel conductors but run two separate 4/0 or 250's to each of the house panels. What 320 socket do you use?

IF I do solar, it would not be backfed to POCO so with this scenario, I'd need to keep the systems separate per building so they'd be downstream from the disconnect, same with generator I guess.
Click to expand...
We use milbanks in central NY. They have a lever bypass and 3/7 studs on the load side. I usually use crimp lugs in these, but you can bolt on multi port mechanical lugs too.
 
bmaclaff said:
Little Bill, we are just out of Chattanooga and the town just adopted 2023.
Thanks, Electrofelon, yeah, 230.40 ex3 sounds workable. then I'd use a couple of 200A disconnects per building, run 4/0 a few feet to the shop panels and then not mess with parallel conductors but run two separate 4/0 or 250's to each of the house panels. What 320 socket do you use?

IF I do solar, it would not be backfed to POCO so with this scenario, I'd need to keep the systems separate per building so they'd be downstream from the disconnect, same with generator I guess.
Click to expand...
You cannot use 4/0 to a shop, if you'reusing alum. That is not a dwelling and per NEC is not subject to the de rate option that a dwelling is. You will have to run 250alum for full 200amp feeder to the shop. Atleast thats how it works in oregon

Kasey
 
KaseyField01 said:
You cannot use 4/0 to a shop, if you'reusing alum. That is not a dwelling and per NEC is not subject to the de rate option that a dwelling is. You will have to run 250alum for full 200amp feeder to the shop. Atleast thats how it works in oregon

Kasey
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#4/0 is rated for 180 amps with the next size up rule you can protect the feeder at 200 amps. Is there is reason why this isn't code compliant?
 
infinity said:
#4/0 is rated for 180 amps with the next size up rule you can protect the feeder at 200 amps. Is there is reason why this isn't code compliant?
Click to expand...

In oregon you will get called on it all day. 4/0 alum is used for a service feeder to a dwelling for de rate. A shop is not a dwelling, its an auxiliary building which means it has to be fed with full load amperage, atleast thats how I read it in the code. And how the inspectors see it here. They are under the understanding that your reference for next size up with be for brand circuits, not a service entrance conductor.

Kasey
 
KaseyField01 said:
In oregon you will get called on it all day. 4/0 alum is used for a service feeder to a dwelling for de rate. A shop is not a dwelling, its an auxiliary building which means it has to be fed with full load amperage, atleast thats how I read it in the code. And how the inspectors see it here. They are under the understanding that your reference for next size up with be for brand circuits, not a service entrance conductor.

Kasey
Click to expand...
You can use 4/0 Al PER CODE on a 200A breaker as long as the load isn't more than 180A. There is no 180A breaker so the next size up rule that infinity mentioned comes into play.
 
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