310.15 (B)(7)

[A/A Fuel GTX]

Need some clarification on an overhead, 200 Amp service, feeding a 2 position meter socket on a duplex dwelling unit. Each unit has 100 Amp service entrance conductors from the load side of the meter socket. Copper conductors used. 2/0 service entrance conductors from the weather head to the line side of the meter socket. #4 service entrance conductors from the load side of the meter socket to the individual main breaker panels located nearest the point of entry in each dwelling. Correct?

 

[Smart $]

Yes. :happyyes:

 

[MasterTheNEC]

I disagree. I do not believe 310.15 (B)(7) can be applied to the conductors from the service point to the line side of the meters. I do agree 310.15 (B)(7) can be utilized from the meter(s) to the individual dwelling units.

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[Smart $]

I disagree. I do not believe 310.15 (B)(7) can be applied to the conductors from the service point to the line side of the meters. I do agree 310.15 (B)(7) can be utilized from the meter(s) to the individual dwelling units.

I agree Code does not cover, per se, the combined load service entrance conductor.

So let's apply a little logic to this scenario because I do not believe the intent is to require the combined load service entrance conductor to be sized otherwise. The normal ampacity of the permitted #4 is 70A @ 60°C. The normal ampacity of #2/0 @ 60°C is 145A, more than double the tapped conductors. Just a little common sense at play.

 

[MasterTheNEC]

So you wish to apply common sense to code language and get an inspector to agree? My statement is simply about the application itself...per the NEC. Can you not see an inspector requiring 3/0 CU from weatherhead to meter group.

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[rhovee]

I have got beat up on this before in the City of Seattle. They get really hung up on the "entire load of the dwelling" portion of the code. I can not run parallel 4/0-4/0-2/0 from a 320 meter to disconnects because it doesn't serve the entire load. Same with sub panels pulled off a main panel in a house, can't use the table because it doesn't serve the entire load. YES you can do a load calculation and pull service entrance conductors rated for that load not the max load of the meter or meter bank. BUT, i have been required to place a phenolic label for max ampacity of conductors. For instance, i had a 5 pack meter base and could only get it in 600 amp rated. Had a load for 81 amps per unit with a house panel. I didn't want to run 600 amps of service entrance, so ran 2 sets of 250 mcm to get 400 and called it a day.

 

[Smart $]

So you wish to apply common sense to code language and get an inspector to agree? My statement is simply about the application itself...per the NEC. Can you not see an inspector requiring 3/0 CU from weatherhead to meter group?

I can. I can also see an inspector allowing 2/0.

 

[curt swartz]

I would guess if the calculated load for each dwelling unit is 100 amps or less the combine load of the feeder supplying both units is less that the ampacity of 2/0 copper (175 amps).

 

[MasterTheNEC]

Point is....no calculated loads are provided in the question. We answer the question as presented. Most AHJ's are going to expect 3/0 CU in this example unless expressed otherwise.

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[kwired]

I would guess if the calculated load for each dwelling unit is 100 amps or less the combine load of the feeder supplying both units is less that the ampacity of 2/0 copper (175 amps).

There is the aspect that makes all the difference in the world.

If total load calculation is only 85 amps, then that common service conductor could be 4 AWG, though it seems wrong it is in compliance with NEC.