400 amp service

[charlie]

Re: 400 amp service

OK, now I am cheating. The following is from the NEC Handbook.

"If a single set of 3-wire, single-phase, service-entrance conductors in raceway or cable supplies a one-family, two-family, or multifamily dwelling, the reduced conductor size permitted by 310.15(B)(6) is applicable to the service-entrance conductors, service-lateral conductors, or any feeder conductors that supply the main power feeder to a dwelling unit.

This section permits the main feeder to a dwelling unit to be sized according to the conductor sizes in Table 310.15(B)(6) even if other loads, such as ac units and pool loads, are fed from the same service. The feeder conductors to a dwelling unit are not required to be larger than its service-entrance conductors.

Exhibits 310.7 and 310.8 illustrate the application of 310.15(B)(6). In Exhibit 310.7, the reduced conductor size permitted is applicable to the service-entrance conductors run to each apartment from the meters. In Exhibit 310.8, the reduced conductor size permitted is also applicable to the feeder conductors run to each apartment from the service disconnecting means, because these feeders carry the entire load to each apartment."

 

[dbj]

Re: 400 amp service

My understanding is any wire after the first main is considered sub-feeders which in turn refers you to 310-16.

 

[hurk27]

Re: 400 amp service

So Charlie since it does say that each SE to each apt. is allowed the reduction of 310.15(B)(6) why wouldn't it be allowed for the feeders from the 400 amp service since the load at the end of the feeders are the same as if there was only a 200 amp service and one disconnect? or are you now agreeing with it?


Dbj read 310.15(B)(6) and you will see that it says even the feeders from the disconnect to the main lighting/appliance panel are allowed the reduced sized wire of table 310.15(B)(6)

the main power feeder shall be the feeder(s) between the main disconnect and the lighting and appliance branch-circuit panelboard(s)

This is an exact quote from the article.

 

[charlie]

Re: 400 amp service

Wayne, I agree that if the main power feeder were to feed the same types of loads that are intended, it would meet the intent of the Code. However, if each panelboard were picking up different types of loads, only one could be the main power feeder.

Example:
In my home, I have 2 - 200 ampere panelboards fed from a 320 ampere meter fitting. One of these has the heat pump, all the backup coils and fan in the electric furnace, and the water heater. The other panelboard has everything else.

IMHO, the main power feeder goes to the second panelboard and the first one should be sized with Table 310.16. My opinion is based on the normal loads that would be seen by a home that was not total electric.

 

[roger]

Re: 400 amp service

Charlie, as you say, your second panel would not meet the definition of "lighting appliance branch-circuit panel" therfore it would be a "Power Panelboard" (408.14(B)) and it's feeder would need to be sized per 310.16.

If both panels met the definition per 408.14(A) they would both be allowed to use 310.15(B)(6)

Roger

 

[don_resqcapt19]

Re: 400 amp service

The problem I have with this section is the definition of "main power feeder". There is nothing in the definition that says that the main power feeder(s) must supply the "main power" to the dwelling unit. The only requirement is that this feeder be between the main disconnect and the lighting and appliance branch circuit panelboard(s). If the code intends that this "main power feeder" actually be the "main feed" to the dwelling unit, why doesn't the definition support this?.
Don