Def. of size of service and entrance conductors for a 400/320 main service panel

[Frank44]

I am currently retired (IBEW Local 3, AFSCME Local 444) and was asked to following question by my friend:

The panel is a Square D SU3040D400CB, with two 200 amp breakers. (Large house and woodworking shop with high demand, both under construction. I have not seen his load calcs.)

His electrician pulled 350 Kcmil AL service-entrance conductors, I would guess based on a calculation of 83 percent of the meter's continuous rating of 320 amps. The AHJ tagged the service-entrance conductors as too small, no further explanation. (I suspect he is defining the size of the service as 400 amp).

What is the correct definition of the service and size of the service-entrance conductors. I have seen conflicting responses on the forum.

Thanks all.

 

[jumper]

The size of the service conductors is according to the calculated load, 230.42(A).

The calculated load is determined by article 220.

There are minimum sizes required for certain occupancies/usage, 230.42(B).

 

[Dennis Alwon]

Are you saying he ran 350 kcm aluminum for 320 amps? The3 table shows 350's are only good for 250 amps at 75C

 

[Ingenieur]

who installed them?
his guy or the utility?

 

[electrofelon]

If there are multiple service disconnects, then the conductors only need to be sized to the load calc and have nothing to do with the OCPD's. Not sure what you have there, don't know that part number off the top of my head.

 

[Frank44]

To your points

To your points

As I said I don't know the calcs for load, just curious why the AHJ failed the install.

It is 350 Kmcil Al XHHW-2, 266 A.

His guy, not utility.

Panel is pretty common our here in the land of the mega mansions. 200 A with 30 spaces, extra 200 A to feed shop.

 

[electrofelon]

As I said I don't know the calcs for load, just curious why the AHJ failed the install.

It is 350 Kmcil Al XHHW-2, 266 A.

His guy, not utility.

Panel is pretty common our here in the land of the mega mansions. 200 A with 30 spaces, extra 200 A to feed shop.

Details are kinda sparse. I think you have a meter main with 2 mains (service disconnects). I also assume you are talking about the conductors on the line side of the meter. If so, the installation would be compliant if the load calc is 250 amps or under. See 230.90 exception 2.

 

[wwhitney]

Details are kinda sparse. I think you have a meter main with 2 mains (service disconnects). I also assume you are talking about the conductors on the line side of the meter. If so, the installation would be compliant if the load calc is 250 amps or under. See 230.90 exception 2.

Since it is a dwelling unit, wouldn't the 83% allowance still apply, so the load calc could be up to 250 / 83% = 310 amps?

Cheers, Wayne

 

[electrofelon]

Since it is a dwelling unit, wouldn't the 83% allowance still apply, so the load calc could be up to 250 / 83% = 310 amps?

Cheers, Wayne

Maybe. I was thinking the shop was a separate structure in which case the conductors would not be serving solely the entire load of a dwelling unit. However I reread the OP and it isnt really clear if the shop is part of the house or not.

 

[Dennis Alwon]

The 83% applies to the riser but I am uncertain if those are the conductors we are addressing. If so, then those conductors can use the 83% but must be sized for 332 amps.

You cannot use the 90C rating in the table as the termination on the meter or load center will limit the ampacity of the conductors to 75C

 

[kwired]

If there are multiple service disconnects, then the conductors only need to be sized to the load calc and have nothing to do with the OCPD's. Not sure what you have there, don't know that part number off the top of my head.

The code that allows that is 230.90(A) exception 3.

Single 400 amp breaker - OP must have 400 amp conductors, possibly 83% if 310.15(B)(7) can apply but the presence of the shop likely disqualifies using that for anything but the 200 amp feeder to the house.

Two 200 amp breakers - he could legally only install 1 AWG if load calculation were only 100 amps even though there is a total of 200 amps overcurent devices, yet conductors on load side of those must be 200 amp conductors (83% on the one supplying the dwelling).

 

[Frank44]

om

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To electrofelon: it is one structure

To Dennis: we are addressing the service-entrance conductors which terminate on the line side of the meter. I believe the electrician MISTAKENLY sized the conductors based on the following: 83 percent of 320 amps at 90 degree C. That would allow 350 XHHW-2.

Corrected would be 83 percent of 400 amps (332) at 75 degree C.

Dennis: could you please give me the code reference for adjusting the ampacity to the 75 degree rating because of the meter termination. It's not my job, but if I can point him in the right direction it will save my buddy some grief.

Thanks to all.

 

[kwired]

To electrofelon: it is one structure

To Dennis: we are addressing the service-entrance conductors which terminate on the line side of the meter. I believe the electrician MISTAKENLY sized the conductors based on the following: 83 percent of 320 amps at 90 degree C. That would allow 350 XHHW-2.

Corrected would be 83 percent of 400 amps (332) at 75 degree C.

Dennis: could you please give me the code reference for adjusting the ampacity to the 75 degree rating because of the meter termination. It's not my job, but if I can point him in the right direction it will save my buddy some grief.

Thanks to all.

See 110.14(C).

Most under 600 volt terminations are rated 75C these days.

 

[electrofelon]

To electrofelon: it is one structure

To Dennis: we are addressing the service-entrance conductors which terminate on the line side of the meter. I believe the electrician MISTAKENLY sized the conductors based on the following: 83 percent of 320 amps at 90 degree C. That would allow 350 XHHW-2.

Corrected would be 83 percent of 400 amps (332) at 75 degree C.

Dennis: could you please give me the code reference for adjusting the ampacity to the 75 degree rating because of the meter termination. It's not my job, but if I can point him in the right direction it will save my buddy some grief.

Thanks to all.

Ok so if it is one dwelling unit structure we can apply the 83% rule. That would be 301 amps so if the load was under than you could have a 350 amp breaker. You still havent clarified if there is 1 or 2 disconnects though.