# Multi-family service size question



## Southeast Power (Jan 18, 2009)

It isn't a SFH, therefore it should be an other type dwelling.
I had the same situation. the plans examiner made me use a 100 amp main and let me keep the small feeder going to the interior panel.


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## HackWork (Oct 2, 2009)

I need to state the electrical service size of a house for official reasons. 

As far as I understand, if there is no main breaker for the entire service in a multi-family dwelling, that the service size is the allowable ampacity of the service entrance conductors.


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## Signal1 (Feb 10, 2016)

In that case it would be a 75A service. (60deg column #2 AL=75A).

For it to be 100A you'd need 1/0. 310.15(B)(7) only applies to the conductors for each dwelling unit.


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## HackWork (Oct 2, 2009)

Signal1 said:


> In that case it would be a 75A service. (60deg column #2 AL=75A).
> 
> For it to be 100A you'd need 1/0. 310.15(B)(7) only applies to the conductors for each dwelling unit.


Hmmmm, that is something to think about.

So all the 200A 2-family services that I installed with the standard 4/0 AL were actually 180A services? Damn, I am going to have a lot of mad customers :laughing:


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## Signal1 (Feb 10, 2016)

From what I read yes, you porked them.

Reading from the 2011 it says "for individual dwelling units of one family, two family and multi family dwellings conductors, you can use the table 310.15(B)(6) In the 2014 handbook, the table disappears but the language it essentially the same only it uses that 83% calculation. It's wording now is "the entire load associated with an individual dwelling in a two or multifamily"

AFAIK for the service on a multi- conductors need to be full size, 60deg for 100 and below, 75 deg for over 100A.

Here's a good article on the subject:http://iaeimagazine.org/magazine/2013/05/16/whats-happening-to-table-310-15b7/


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## Signal1 (Feb 10, 2016)

One more thing, if you do a lot of work in urban areas, watch out for 120/208 single phase services. 
The reduction calculation is not allowed there, it must be 120/240v 3 wire.


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## telsa (May 22, 2015)

HackWork said:


> I'd just like to confirm this.
> 
> *A 2-family house*, a main panel for each unit, both panels have a 40A main breaker.
> The SEC's feeding the meter pan are #2 Al. Then #6 or #8 goes from each meter to the main panel.
> ...


*
A duplex ?*
*
Or is this a case where the families are allocated separate floors in an old BIG home -- that's been reworked, a LOT ?*


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## telsa (May 22, 2015)

HackWork said:


> Hmmmm, that is something to think about.
> *So all the 200A 2-family services that I installed with the standard 4/0 AL were actually 180A services? Damn, I am going to have a lot of mad customers* :laughing:


The Poco does not have to obey the NEC.

And they sure don't.

As a practical engineering matter, Pocos treat O/H drops as being in free air -- to include that last drop inside the riser.

Of course, we don't have that latitude.


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## HackWork (Oct 2, 2009)

This has nothing to do with the PoCo.


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