Status
Not open for further replies.

#### Electron_Sam78

##### Senior Member
Hey I just want some feedback on these calcs. for services

I'm thinking 400a services including 400a main breakers. USE/RHW dual rated, paralleled, 4/0 copper conductors with 460a total ampacity - adjusted for ambient temps of up to 104 degrees = 404.8 ampacity

#### cpal

##### Senior Member
why would you not parallel 3/0's??

#### Electron_Sam78

##### Senior Member
They didn't add up to enough ampacity after applying the correction factor for ambient temp. At least I thought they didn't. PLease correct if wrong.

#### cpal

##### Senior Member
Sorry, I didn't see the 104 F

#### dana1028

##### Senior Member

Here is a code section I've never really fully understood.

230.42(A) - The ampacity of the service entrance conductors before the application of any adjustment or correction factors shall not be less than:

(1) The sum of the noncontinuous loads + 125% of continuous loads.

As cpal had mentioned above - why not parallel 3/0s? Before the application of adjustment factors these conductors have a value of 400A in the 75-degree column.

I know after adjustment/correction factors they have only a 364A value - but that's not what 230.42(A) says -is it?

Thanx for any feedback.

##### Senior Member
Here is a code section I've never really fully understood.

230.42(A) - The ampacity of the service entrance conductors before the application of any adjustment or correction factors shall not be less than:

(1) The sum of the noncontinuous loads + 125% of continuous loads.
....

My response is "The sum of..." (IE minimum = met) then go back and apply some factors... see what one gets, or other...

#### Electron_Sam78

##### Senior Member
Here is a code section I've never really fully understood.

230.42(A) - The ampacity of the service entrance conductors before the application of any adjustment or correction factors shall not be less than:

(1) The sum of the noncontinuous loads + 125% of continuous loads.

As cpal had mentioned above - why not parallel 3/0s? Before the application of adjustment factors these conductors have a value of 400A in the 75-degree column.

I know after adjustment/correction factors they have only a 364A value - but that's not what 230.42(A) says -is it?

Thanx for any feedback.

#### Smart \$

##### Esteemed Member
Undersize is a subjective term when trying to nail it to NEC requirements :grin:

If the wire sizing is based on the sum of non-continuous plus 125% of continuous loads, you already have a built in margin, and a lenient one at that, for the sum is correlated to every load being on at the same time, all the time, which in most of our realities D) will never occur.

Staff member