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crankcase 09-20-2010 11:29 PM

Really long secondary run to service detached garage
I am looking to run my own secondary line service to a detached garage. I need to go 275' direct burial from the transformer to my meter. If I use 4/0 4/0 2/0 aluminum will my voltage drop be too great to allow a 200A main service at the garage? Otherwise I would go 150A main service. If I need to go this way will 4/0 fit under the lugs on a 150A Square D QO panel, otherwise I can go copper from meter to panel?

crankcase 09-21-2010 12:02 AM

Just to clarify...
My service to the house is 200A but I am running the following: electric freestanding range, electric dryer, central AC, 15Kw off-peak electric boiler, future wall oven, future 2nd electric dryer

28'x34' Detached will have 9Kw off-peak electric boiler, window AC, 12-20gallon electric water heater, 220V air compressor, future welder. There will be some small appliances and such as 1/3 of the space will be office/living quarters.

frenchelectrican 09-21-2010 01:58 AM

Ok I have to get couple figure crushed together and is your meter box located at the house or what ??

275 feet from POCO transfomer to your meter genrally will be done by POCO unless you have CO-OP POCO they may wavier it a little.

Is your transfomer is overhead or padmounted transfomer?

And both house and garage will have seperated meter or one meter for both ?

If both you will end up some issue with metering size due the load it pretty much close to the limit due you have 15KW electric boiler and you will plan to have 9 KW electric boiler as well that is 100 amp right there alone.{ on 240 volt load }

If you want to stay with single meter set up you will have to increase from 200 amp to class 320 meter socket size { basically a 400 amp resdential verison } and you may want to give the POCO a head up in case they may have to change the transfomer size as well.

For the underground cable the 120mm˛ { 4/0 AWG } Alum URD should work ok with that distance and I think that is pretty close to the limit for the URD to run that far otherwise the POCO may want to put a transfomer closer to the garage you want to set up.

The 200 amp SqD breaker will take the 120mm˛ conductor without issue and I am pretty sure the 150 amp verison is the same but I will have to look at the catalog book to verify it.


crankcase 09-21-2010 01:38 PM

It's a pad mounted transformer. I told the staking engineer what my plans were when they set the transformer so it is properly sized for everything. I believe 37KV, i'd have to look again for sure. I could have went with the 320A, but I didn't want to pony up the extra $1800 right away for the upgrade. I figured that because it's not my only means of electricity at the property, I could do for now until I get this all sorted out.
CO-OP wants $1500 to bring out their trencher if they do the work. Not including the cable! They say they very rarely do it.

frenchelectrican 09-21-2010 08:44 PM

Is your electric meter is at your house ? if so which way is shorter from the house meter or from the transfomer pad ?

If you are shorter from the house it will easy to swap over to 320 service but nice gotha is the POCO have to change the lateral { underground run } to handle addtional load otherwise you can run second lateral to the garage which it will have it own meter.

The 37Kw is 37,000 watt transfomer that is plenty big for 400 amp service normally most home use either 15 or 25 Kw transfomer depending on 100 or 200 amp service.


crankcase 09-21-2010 09:29 PM

Yes the meter is on the house. It would be shorter to run to the transformer. I already ran 2" conduit under the blacktop driveway so I wouldn't have to bust it up running the line. I just didn't think about the possible voltage drop running 275' And even if I had to run a 150A because of voltage drop, I would think I still have more than enough capacity. The only way that I may be shorter would be if I was to run a 320A main at the house and run my garage service line through the house, then go underground to the detached garage.

frenchelectrican 09-21-2010 09:47 PM

I get your point with that issue and with 275 feet I did came up a figure or two with 150 amp main breaker size you will be fine with 120mm˛ { 4/0 AWG } alum verison but it will get very iffy when you go with 200 amp you will have to bump up to 150mm˛{250KCM} with that distance.

and the load you have in detached garage the 150A verison will meet that without issue

But check with your CO-OP to see if they allowed second meter on your property if not the other suggest is use the CT { current transfomer } metering at the transfomer and deal from there.


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