Let's try to stay focused on the question. Yes it is for a single family home of 8000 square feet and they have alot going on like hot tubs and steamers and....... Load calc would be around 335 but the owner wants more. The big question is whether 4/0 AL XHHW 75 dgree C in 4 runs through a CT, bonded together in the CT as required by the local electic company is sized appropriately?
800 amp Residential Service
- Thread starter gigawatt
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Jim W in Tampa
Senior Member
- Location
- Tampa Florida
Is the CT on the house ? If yes then you have parallel conducters being they are bonded at both ends. So now 4/0 would not give you 800 amps and you also must look at if they are bundled for more than 2 feet. If they are then derating applies
You can use the 90 degree rating for derating
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
230.2 and its reference to Exception 2 of 230.40 together see this as one service.
If it were not for this sentence in 230.2 the install would not be permitted at all.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
they are not parallel from the CT to each disconnect. If total calculated load is not 800 amps the conductor does not need to be 800 amp conductor.
Why do the lines need connected together at the CT? I don't think I have ever seen this done. Also in CT cabinets around here this is POCO equipment and they do whatever they want in there. NEC and electrical inspector do not matter inside that cabinet. POCO usually installs supply side conductors I install load side conductors POCO makes all connections within cabinet. If this were installed where I live I would have the 4-4/0 from CT to service disconnects, and the POCO would likely install single 350 aluminum to supply it, unless there was over 400 amps continuous load then they would likely parallel two 350's or possibly install a single 500. Not real easy to get continuous 400 or more on a single family dwelling though, and there are very few multi million dollar homes around here which could be an exception to that.
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
"The big question is whether 4/0 AL XHHW 75 dgree C in 4 runs through a CT, bonded together in the CT as required by the local electic company is sized appropriately? "
I do not know why they are connected.
As to the CT here we would supply the CT cabinet and run all the wires to transformer.
I see no way to get out of derating because of the CT would group them close for 2 feet.
Now if the install belongs and installed by POCO then might be ok.
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
It is not possible to maintain spacing between conductors inside cabinets?
- Location
- Massachusetts
Derating does not apply inside cabinets and enclosures.
Jim W in Tampa
Senior Member
- Location
- Tampa Florida
Not saying your wrong but how about a code number.
And if that fixes that issue then i think he is good to go with 4 seperate feeds. Seems way over kill for a house but then just perhaps there are loads being added that we do not know about. Perhaps he has a grow house. Lot of extra money for service twice his needs.
- Location
- Massachusetts
Check out 310.15(B)(2) and notice it only applies to raceways and cables.
I don't think so since they are being feed from a CT cabinet. I have done one home that had a 1200 amp service.Ridiculous but that's what it took.
what was the sq ft of the house?
- Location
- Chapel Hill, NC
- Occupation
- Retired Electrical Contractor
hillbilly1
Senior Member
- Location
- North Georgia mountains
- Occupation
- Owner/electrical contractor
We did one in Albany, Ga. that had a 480 volt three phase service, if I remember correctly there was a 75 kva transformer on each floor, three storys, This was his personal hunting lodge, I think it was 3-4 very large bedrooms with a full commercial kitchen in the basement. It was modeled after a southern mansion, and yes this guy had more money than he knew what to do with, you should have seen his fishing boat!
kwired
Electron manager
- Location
- NE Nebraska
- Occupation
- EC
I did a home once with 4 - 200 amp feeds from a padmount transformer 75 to 100 feet of lateral conductors. Don't remember calculated load but 400 amps may have been enough there was a lot of electric heat so maybe 600. Still needed enough circuits that 4 panels were going to be needed (elimination of the 42 circuit rule in 2008 could change this if it were done to 2008 code). At that time I figured that it cost less to run the four 200 amp feeds than it would cost to run a 400 amp feed - install a 400 amp fused switch or breaker - install wireways to connect it all together and still would need the same 4 main breaker panels or main lug panels with 400 amp busses.
As it is installed now there is plenty of extra capacity for future loads also.
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