Residential wire size

[nizak]

I’m installing a 200 amp service on a new dwelling.
Conductors from meter base to service rated transfer switch are 3/0 CU.

Conductors from transfer switch to 200 amp feed through outdoor load center that will be supplying an 100 amp load center in the attached garage are 3/0 CU.
( I have 3/0 CU left over from a prior job, I realize 2/0 CU is compliant for this portion of wiring)

From the feed through load center I have just under 150’ to feed the 200 amp load center located in the basement of the dwelling.

My question is: Would I need 250 AL or could I use 4/0 AL for that?

I feel 250 is the correct answer.

I’m not saying 250 for VD reasons I’m saying it because it’s not supplying 100% of the dwelling.

Another contractor I know is adamant that 4/0 is compliant.

Am I incorrect?

Thanks

 

[augie47]

You are correct in that if you are not supplying the full load associated with the dwelling you can not use the 83% rule, however, your feeder only has to be rated to carry the load. A 4/0AL has a 180 amp rating and 240.4 will allow the 200 amp OCP. In rare instances you might need to show your calculated load does not exceed 180 amps.

 

[nizak]

Thank you. I’m estimating about 60 amps of load will be connected to the 100 amp garage load center.

So that will reduce the house panel load to around 120 max.

My initial calculation came in right around 180 amps . Owners are still kicking around possibly adding a small outdoor “ kitchen area”.

That could skew my number a bit.