Wire size for 250 amp service

[Southla]

This is for a small office. The engineer says it has to be a 250 amp service using 3-0 copper wire
The load calculations I did I came up with 150 amp load. Building is less than 2800 sq/ feet and it just offices for 5 people.
Inspector failed my 200 amp 240V single phase service with 3-0 wire, because the engineer said it needs 250 even though I showed him my load calculations.
So I installed a 6’ tall 400 amp capacity semens panel board with a down sized 250 amp main breaker.
He passed the service and panel all good this time. I used 4-0 copper and 2 10’ ground rods with #2 wire.

This panel is 35’ from the inside sub panel
I was going to run 4/0 copper for the hot 3/0 for the neutral and #2 for the ground. Wanted to get another opinion on this. There are no unbalanced loads
Inspection is not going to know any better because he said 3/0 was a good wire size.
Thank you for any help.

 

[zbang]

When the engineer and plans say 250 amp, install 250 amp and move on, there's nothing to be gained by redesigning things unless the engineer or client ask for it; it's their money to spend.

There are no unbalanced loads

If this is an office with 120v circuits there will be an unbalanced load unless you have a 240-240/120 volt transformers in there. May not be much, but it'll be there.

 

[infinity]

The engineer says it has to be a 250 amp service using 3-0 copper wire

You cannot use #3/0 for a 250 amp service for an office building.

250 amp main breaker.
I used 4-0 copper and 2 10’ ground rods with #2 wire.

#4/0 is rated for 230 amps so you can go up to the next standard size of 250 amps if the load calculation is 230 amps or less. Ground rods only require a #6 GEC but over-sizing with #2 is permitted.

 

[Southla]

When the engineer and plans say 250 amp, install 250 amp and move on, there's nothing to be gained by redesigning things unless the engineer or client ask for it; it's their money to spend.


If this is an office with 120v circuits there will be an unbalanced load unless you have a 240-240/120 volt transformers in there. May not be much, but it'll be there.

Thanks. I was trying to save money for the client that why I tried to go for the 200 amp.
Yes that is correct I will have some that is not balanced. Thank you.

 

[Southla]

You cannot use #3/0 for a 250 amp service for an office building.

#4/0 is rated for 230 amps so you can go up to the next standard size of 250 amps if the load calculation is 230 amps or less. Ground rods only require a #6 GEC but over-sizing with #2 is permitted.

Thanks I knew 3-0 would be too small. I went with the #2 because he had that and the 3/4 ground rods on the plan.

 

[Little Bill]

Engineer must be getting paid a % of the cost the way he oversized everything.