New 2 family service

[Primarycontractinginc.]

Electrical Inspector is telling me I must use 350KCMIL for Parallel feeders to the 400amp meter feeding 2 -200amp services (2 family House) for the over head service? I have pulled 300's Aluminum in Parallel ?

 

[nizak]

Electrical Inspector is telling me I must use 350KCMIL for Parallel feeders to the 400amp meter feeding 2 -200amp services (2 family House) for the over head service? I have pulled 300's Aluminum in Parallel ?

What is his basis for this?

 

[Primarycontractinginc.]

He says I can’t use the 83% rule because there are more the 4 current carrying conductors

 

[don_resqcapt19]

Parallel 250 kcmil aluminum would be fine as long as they are not in the same raceway. Parallel 300 kcmil aluminum is fine in the same raceway as the adjusted ampacity for 4 current carrying conductors is 208 amps giving you 416 amps total. Is the inspector applying the ampacity adjustment to the wrong column?

You can never use the 83% ampacity for the service entrance conductors that supply more than one meter. That rule is only for service conductors or feeders that supply a single dwelling unit.

 

[Primarycontractinginc.]

Is that the 75 degree column?

 

[don_resqcapt19]

Is that the 75 degree column?

The ampacity adjustment for most conductors is based on the 90°C column. What is the insulation type of the conductors you are using?

 

[Primarycontractinginc.]

XHHW

 

[tortuga]

Electrical Inspector is telling me I must use 350KCMIL for Parallel feeders to the 400amp meter feeding 2 -200amp services (2 family House) for the over head service? I have pulled 300's Aluminum in Parallel ?

As don said 310.12 (83% rule) does not apply to the service for a two family dwelling.
If you dont mind sharing your load calculation we can see how the numbers work out for what you installed.
EDIT I missed the parallel part, so you have install two sets of 300's ? 6 conductors? That should be fine no matter what.

 

[don_resqcapt19]

XHHW

If it is just XHHW, then your inspector is correct as the ampacity adjustment would be from the 75°C column giving you an adjusted ampacity of 368 amps for paralleled 300 kcmil aluminum. Paralleled 350s would have an adjusted ampacity of 400 amps for 2 sets in parallel.
I did my original calculations based on the 90°C column because most conductors are so rated.
Are you sure your conductor is not XHHW-2?

 

[Primarycontractinginc.]

My insulation is XHHW-2
Thanks so
Much for your help!

 

[don_resqcapt19]

My insulation is XHHW-2
Thanks so
Much for your help!

Then the ampacity adjustment is based on the 90°C column and my calculations in post #4 are correct.

 

[tortuga]

If say it was XHHW and your calculated load was 368 amps or less it should also pass code, the service conductors need not meet the sum of the OCPD's if a proper load calc has been done. I'd bet a milkshake if we ran the numbers you could use a single set of 500 AL's with a reduced neutral, but whats installed is future proof which is good.

 

[infinity]

What's the calculated load? If it's 230 amps or less you can use one set of 300's.

 

[Primarycontractinginc.]

Inspector has conceded to the 90 degree column using 300’s XHHW-2
So we are all set, current installation has passed