large residential service questions

fisherelectric

Senior Member
Location
Northern Va
I have been asked to design the service for a big house. Service is to be 800 amps. The CT cabinet is to be located in a small building about 50' from the main house. There will also be a large detached garage/apartment about 100' away that will require 200 amps. They want to install the service equipment in the small building with the CT cabinet rather than in the house. My first thought was to use a 6 breaker I-Line panelboard as the service with 4 200 amp breakers and run 3 sets of 250 with #4 equipment ground into the house and one set to the garage. But after looking at 225.30 I have doubts this would be compliant and I would have to run 1 600 amp feeder to the house, set a trough and feed disconnects that way.
However, if I could talk them into putting the service in the house rather than out next to the CT cabinet, according to 230.4 excep #2 I could run 4 sets of 200 amp service entrance conductors directly from the CT cabinet into the house into disconnects and then feed the garage from there. That would seem to be a lot more cost effective.
So if they stick to their plan of putting the service equipment next to the CT cabinet I would have to install a 600 amp disconnect for the house and a 200 amp disconnect for the garage at the CT cabinet in addition to disconnects at both the house and garage.
Any thoughts would be appreciated.
 

augie47

Moderator
Staff member
Location
Tennessee
My first thought would be to see if you can mount the CT on the outside of that building, keep all you wiring on the outside, then you could run whatever services you desired to the house and garage.
 

fisherelectric

Senior Member
Location
Northern Va
The architect and homeowner have nixed putting the CT cabinet on or in the house. I think they don't realize that putting the service in the small building really doesn't gain them anything except a much bigger expense since they will still need disconnects, just like a service, in the house and garage. The only difference is that they will have to trench further to feed the garage, which is still way cheaper than adding service equipment next to the CT cabinet. I just want to make sure I am correct in how I am interpreting 225. versus 230. as regards running feeders to the house as opposed to service conductors. Running 4 2" or 21/2" conduits from the CT to the house terminating in disconnects is going to be way cheaper than building a service outside with a 600 amp disconnect and a 200 amp disconnect, then running a 600 amp feeder to the house and 200 amp feeder to the garage. Am I missing something?
 

Smart $

Esteemed Member
Location
Ohio
The architect and homeowner have nixed putting the CT cabinet on or in the house. I think they don't realize that putting the service in the small building really doesn't gain them anything except a much bigger expense since they will still need disconnects, just like a service, in the house and garage. The only difference is that they will have to trench further to feed the garage, which is still way cheaper than adding service equipment next to the CT cabinet. I just want to make sure I am correct in how I am interpreting 225. versus 230. as regards running feeders to the house as opposed to service conductors. Running 4 2" or 21/2" conduits from the CT to the house terminating in disconnects is going to be way cheaper than building a service outside with a 600 amp disconnect and a 200 amp disconnect, then running a 600 amp feeder to the house and 200 amp feeder to the garage. Am I missing something?
Why bother trying to save the customer money if they know what they want? Just give them what they want, as long as it is Code compliant, and charge accordingly.
 

fisherelectric

Senior Member
Location
Northern Va
Because I am bidding this job so it will pay me to find the least expensive way to give them what they want. They want the CT cabinet in a separate building, but the service location is negotiable. Apparently they have no EE and in the scope they just wrote "800 amp service" and asked for "suggestions". I'm not sure where they came up with the idea of putting the service in the out building, but I suspect it may have come from someone else who is bidding this job. I just want to make sure my interpretation of 225.30 versus 230.4 ex #2 is correct and I am not missing anything.
 
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kwired

Electron manager
Location
NE Nebraska
Because I am bidding this job so it will pay me to find the least expensive way to give them what they want. They want the CT cabinet in a separate building, but the service location is negotiable. Apparently they have no EE and in the scope they just wrote "800 amp service" and asked for "suggestions". I'm not sure where they came up with the idea of putting the service in the out building, but I suspect it may have come from someone else who is bidding this job. I just want to make sure my interpretation of 225.30 versus 230.4 ex #2 is correct and I am not missing anything.
Who came up with the "800 amps service"?

Did you do any load calculations?

I'm guessing they want CT cabinet inside for aesthetic reasons. Does POCO allow for metering equipment to be inside? Some do not.
 

texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I have been asked to design the service for a big house. Service is to be 800 amps. The CT cabinet is to be located in a small building about 50' from the main house. There will also be a large detached garage/apartment about 100' away that will require 200 amps. They want to install the service equipment in the small building with the CT cabinet rather than in the house. My first thought was to use a 6 breaker I-Line panelboard as the service with 4 200 amp breakers and run 3 sets of 250 with #4 equipment ground into the house and one set to the garage. But after looking at 225.30 I have doubts this would be compliant and I would have to run 1 600 amp feeder to the house, set a trough and feed disconnects that way.
However, if I could talk them into putting the service in the house rather than out next to the CT cabinet, according to 230.4 excep #2 I could run 4 sets of 200 amp service entrance conductors directly from the CT cabinet into the house into disconnects and then feed the garage from there. That would seem to be a lot more cost effective.
So if they stick to their plan of putting the service equipment next to the CT cabinet I would have to install a 600 amp disconnect for the house and a 200 amp disconnect for the garage at the CT cabinet in addition to disconnects at both the house and garage.
Any thoughts would be appreciated.
I think that your analysis is correct, this will not meet 225.32. I do think that if you go the the 600 amp disco. route you could locate it just inside, say, as in coming out of the floor of the basement directly into a disco. to keep it out of view and be compliant with 225.32. Even if you ignore the requirement for 1 feeder and use the 3 200's you would still have to have disco. for each on or just inside where the conductors enter. I have seen AHJ's overlook or permit the multiple feeders. On another note, as kwired pointed out, you better check with the POCO about locating the CT can inside the out building. I see many that won't allow this even though it is NEC compliant.
 

fisherelectric

Senior Member
Location
Northern Va
No one has done a load calculation. They did give me HVAC loads and a detailed plan, but no real fixture schedule or equipment loads. Their scope says things like "80 amp sub-panel for pool equipment" which I assume they got from a pool contractor. I figured what I could and came up with less than 600 amps for the house. The garage/apartment doesn't really need 200 amps, but that's what is called for. I have made it clear that a load calc needs to be done before we can get serious and that I would do it for a fee if they give me all the info I need.
Can some one tell me if I am correct that a feeder from a service in an out building to this house would need to be a single feeder, with a disconnect on either end, whereas the service conductors could be several smaller conduits directly from the CT cabinet terminating in several 200 amp disconnects or main breaker loadcenters?

Thanks Texie...posted before I read your reply. Good idea about the POCO. I hadn't really thought about that. Not sure what they have discussed with VA Dominion at this point.
 
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texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
No one has done a load calculation. They did give me HVAC loads and a detailed plan, but no real fixture schedule or equipment loads. Their scope says things like "80 amp sub-panel for pool equipment" which I assume they got from a pool contractor. I figured what I could and came up with less than 600 amps for the house. The garage/apartment doesn't really need 200 amps, but that's what is called for. I have made it clear that a load calc needs to be done before we can get serious and that I would do it for a fee if they give me all the info I need.
Can some one tell me if I am correct that a feeder from a service in an out building to this house would need to be a single feeder, with a disconnect on either end, whereas the service conductors could be several smaller conduits directly from the CT cabinet terminating in several 200 amp disconnects or main breaker loadcenters?
Yes, running service conductors to each building directly from the CT can would be a possible NEC compliant method. But again the POCO may veto this as I see many that require the service disconnecting means to be located adjacent to the meter/CT.
 

fisherelectric

Senior Member
Location
Northern Va
Yes, running service conductors to each building directly from the CT can would be a possible NEC compliant method. But again the POCO may veto this as I see many that require the service disconnecting means to be located adjacent to the meter/CT.
I was thinking run 4 conduits to the house. Set 4 200 amp disconnects and then feed from one of them to the garage. So I need to find out where their discussions with the poco are at this point, and whether the poco will allow the service disconnect(s) to be in a separate building. That may be why they are suggesting service equipment in the out building. thanks.
 

kwired

Electron manager
Location
NE Nebraska
Can some one tell me if I am correct that a feeder from a service in an out building to this house would need to be a single feeder, with a disconnect on either end, whereas the service conductors could be several smaller conduits directly from the CT cabinet terminating in several 200 amp disconnects or main breaker loadcenters?
A building supplied by a feeder still needs a main disconnect. And of course there will be one on the supply end of the feeder otherwise it is a service and not a feeder. It would not have to be a disconnect dedicated specifically to one feeder conductor I guess. Also remember outside feeder taps can be unlimited in length, so you could have a 800 amp service disconnect and feeder taps running to all your buildings if you wanted.

I would still do a load calculation. Like you said they wanted 200 amp to the garage/apartment, which is fine to run a 200 amp supply to it but if you eliminate 100 amps needed here and 100 amps needed at the house and maybe eliminate more elsewhere you are looking at the possibility of only needing 600 amp service instead of 800, but maybe they want 800 anyway just in case.

Remember if the house is fed with a feeder you can only have one feeder, but nothing says you can't run a 400 amp (if that is all load calc calls for) or 600 amp feeder and still have up to six disconnecting means.
 
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texie

Senior Member
Location
Fort Collins, Colorado
Occupation
Electrician, Contractor, Inspector
I was thinking run 4 conduits to the house. Set 4 200 amp disconnects and then feed from one of them to the garage. So I need to find out where their discussions with the poco are at this point, and whether the poco will allow the service disconnect(s) to be in a separate building. That may be why they are suggesting service equipment in the out building. thanks.
The idea of using 1 meter with service conductors to multiple buildings has been discussed here before. This is NEC compliant as the NEC does not say you have to have a disco before, after or near a meter. As someone else here artfully pointed out, a meter is nothing but a "wide spot in the service conductors" and I agree. This issue here is many POCO's won't allow this. My understanding of this is from talking with some POCO's, is that they want to be able to remove the load on a meter for maintenance or repairs without having to go all over looking the discos.
 

kwired

Electron manager
Location
NE Nebraska
The idea of using 1 meter with service conductors to multiple buildings has been discussed here before. This is NEC compliant as the NEC does not say you have to have a disco before, after or near a meter. As someone else here artfully pointed out, a meter is nothing but a "wide spot in the service conductors" and I agree. This issue here is many POCO's won't allow this. My understanding of this is from talking with some POCO's, is that they want to be able to remove the load on a meter for maintenance or repairs without having to go all over looking the discos.
True, but such a service is typically the only service on the transformer also so they can kill the primary side of transformer and everything is dead if they wanted, some are pig headed about such things though. I know I would rather have the ability to cut primary power than plug in a meter and risk having an arc flash incident right in front of me. When they plug in those primary fuses they either have long extension and do so from the ground, or they have at least a 6 foot stick and are not right in immediate vicinity should it blow up.

Oh yeah, since this install is CT metered, pulling/installing the meter is not the same hazard as a self contained meter.
 
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