Check my calculations please!

[Electron_Sam78]

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

388a load and 365a load.

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]

why would you not parallel 3/0's??

 

[Electron_Sam78]

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]

Sorry, I didn't see the 104 F

 

[dana1028]

Explanation please - 230.42(A)

Explanation please - 230.42(A)

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.

 

[cadpoint]

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]

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.

In other words don't undersize your your service entrance conductors or you'll be sorry

 

[Smart $]

In other words don't undersize your your service entrance conductors or you'll be sorry

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.

 

[iwire]

In other words don't undersize your your service entrance conductors or you'll be sorry

It will be tough to be sorry as the power company will figure the load to be about 50% of the NEC load calcs and the power company knows better than anyone what the actual load of a dwelling unit will be.

In other words I agree with Smart$ :smile: