400 AMP service

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Bama_Electrical

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Alabama
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Electrician
I am working on a residential neighborhood wiring one house after the other. There are a couple of houses that will be 400amps. The project manager that I am working with said the inspector would require a larger wire than 4/0 AWG aluminum for the service. It is setup underground to the meter base from the poco. I am being told that we would have to run wire capable of carrying the full 400/320 amps from the meter to the service disconnect and 4/0 AWG could be used from there. Anybody else run into this before?IMG_0177.jpeg
 
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What are the calculated loads for each service and what size conductors are feeding the meter?
 
If it's underground here, the POCO runs the underground to the meter. We usually run 3/0 to each panel from the 320/400A meterbase. I believe the POCO runs 350 MCM Al., but if we had to run it from a single disconnect , we would have to parallel 4/0 or run a huge expensive larger conductor. If you have to have a disconnect before the panels, it's cheaper to set two disconnects @ 200A and run smaller conductors vs a 400A disconnect and larger conductors.
 
Our poco would run a 4/0 triplex for a 400 amp underground service, until they got so many complaints about voltage drop. Apparently they got sued, now they reduced the max length of the secondary, and run 350. I built a 1200 amp service, and they wanted to drop 3-sets of 4/0 to it! Had a meeting with the engineer and the building owner, so they agreed to parallel 4 sets of 350’s. They still didn’t upgrade the existing transformer, and it blew a month later! LOL!
 
Little Bill said:
If it's underground here, the POCO runs the underground to the meter. We usually run 3/0 to each panel from the 320/400A meterbase. I believe the POCO runs 350 MCM Al., but if we had to run it from a single disconnect , we would have to parallel 4/0 or run a huge expensive larger conductor. If you have to have a disconnect before the panels, it's cheaper to set two disconnects @ 200A and run smaller conductors vs a 400A disconnect and larger conductors.
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POCO is bringing 350 mcm to the meter. I will be splitting it to 2 different disconnects from the meter. 1 of the disconnect will be for the home. The other disconnect will run to a 100amp panel for electric vehicle charging and a 100amp utility building panel. It will be setup just like the screenshot above.
 
He's only asking about the conductors from the meter to each disconnect.

The manger is wrong. Those conductors only need to be rated for 200 amps.
 
The only oddball thing with a dual panel 400A service is you can't use the normal dwelling sizing of conductors because neither panel is "serving a dwelling" (each is serving a portion of a dwelling). So if you would normally run 2/0 copper to a 200A panel, you'd need 3/0 copper. 4/0 aluminum may work as its ampacity at 75C is 180A. If your calculated load is 180A or less, and there are no other bundling or derating factors that reduce this below 180A, 4/0 Al is OK. If the calculated load on a panel is over 180A, you'd need to move up a size.

Also watch your ground electrode conductor and water pipe bond size, it needs to be based on the sum of your service conductors or the size of the conductors feeding the meter, whichever is larger. If plastic piping, and Ufer or rods only, then it won't matter.
 
Both of the houses with 400 AMP services have copper piping throughout. The plans show for a Ufer ground with 4 AWG bare copper and a 1/0 copper from the water pipe bonding at each service disconnect
suemarkp said:
Also watch your ground electrode conductor and water pipe bond size, it needs to be based on the sum of your service conductors or the size of the conductors feeding the meter, whichever is larger. If plastic piping, and Ufer or rods only, then it won't matter.
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The inspector is incorrect. You can use 4/0 al, which is rated at 180 amps at 75C, but the calculated load must be 180amps or less then you can use the next size breaker rule 240.4(B)-- Suemarkp already mentioned this.

The water pipes only need #2 and it can be just 1 wire installed at the meter, if power company allows it. If not, then a #4 to each panel is all that is necessary. If specs say differently then you must do what the specs state.
 
@Dennis Alwon So this is the setup for the Ground/Ufer. There is a #4 copper that was clamped to the rebar and comes out from under the slab. It has to be bonded at the Meter per the POCO. Specs are calling for the water pipe to be bonded in both service disconnects. It is showing the water pipe bonding in both, but I thought bonding in one of the disconnects would be sufficient.
 
Bama_Electrical said:
@Dennis Alwon So this is the setup for the Ground/Ufer. There is a #4 copper that was clamped to the rebar and comes out from under the slab. It has to be bonded at the Meter per the POCO. Specs are calling for the water pipe to be bonded in both service disconnects. It is showing the water pipe bonding in both, but I thought bonding in one of the disconnects would be sufficient.
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Imo, one panel is all that is necessary if it is full sized (#2 in this case)but it appears the specs are overkill as they want 1/0 and both panels so you have to do what it calls for anyway.
 
I just helped a friend with his underground. had to run 500mcm AL to the meter. POCO requirements. 310.12 after the meter to the panels.
 
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