help please

[dwellselectric]

Okay I dont know where to look in the code for this answer. But how would I find out what size the lateral would have to be "before the meter" for a 400 amp service with a total cal. load of 155 amps?

 

[charlie]

Basically, you are sizing the service entrance conductors. Just comply with 230.42. Then go to 240.4(B) for the overcurrent protection (the load will be protected on the load end of the service entrance conductors and there will be no short circuit or ground fault protection.

In my opinion, you can install a 175 ampere overcurrent device for the main or up-size the service entrance conductors to 500 kcmil.

 

[dwellselectric]

Basically, you are sizing the service entrance conductors. Just comply with 230.42. Then go to 240.4(B) for the overcurrent protection (the load will be protected on the load end of the service entrance conductors and there will be no short circuit or ground fault protection.

In my opinion, you can install a 175 ampere overcurrent device for the main or up-size the service entrance conductors to 500 kcmil.

I told my boss that he would have to install 500 KCMIL conductors because he is keeping the 400 amp main. But he is telling me no because the full load is 155 amps and he wants to rate the lateral for 155 amps but keep the 400 amp main? I told him that you can't do that unless you change the main breaker but he disagrees with me. So I told him I would ask.

 

[Dennis Alwon]

Well, I think your boss is correct however I would run conductors for the 400 amp size otherwise why install a 400 amp service.

230.31 Size and Rating.
(A) General. Service-lateral conductors shall have sufficient ampacity to carry the current for the load as calculated in accordance with Article 220 and shall have adequate mechanical strength.
(B) Minimum Size. The conductors shall not be smaller than 8 AWG copper or 6 AWG aluminum or copper-clad aluminum.