Apartment panel feed

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Toros

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Tujunga, CA
Hi i am trying to figure out what size wire should I used to feed a sub panel in a apartment unit in 43-unit complex.

I would say:
if panel's load is 80A and located in third floor , 70 feet away from meter,
it would requires #3 thhn, cu @ 60 degree temp. per NEC/CEC: 110.14 (c1)

Am I correct???

Or Should I use 310-15 B7 instead of 310-15 B16 and forget about 110.14 c1



Thanx
 
You need to assure your job meets the criteria spelled out in 310.15(B)(7)
{240/120 single phase, one dwelling unit, etc) and if so you can use that multiplier.
Once you get a result you must still verify that your conductor is no smaller than required by 110.14.
 
augie47 said:
You need to assure your job meets the criteria spelled out in 310.15(B)(7)
{240/120 single phase, one dwelling unit, etc) and if so you can use that multiplier.
Once you get a result you must still verify that your conductor is no smaller than required by 110.14.
Click to expand...
i still do not get it
per 310-15 B7, #4 cu is good enough to feed for 80A- loaded panel
but they said #4 is undersized per 110.14
 
Toros said:
i still do not get it
per 310-15 B7, #4 cu is good enough to feed for 80A- loaded panel
but they said #4 is undersized per 110.14
Click to expand...
110.14 directs you to Table 310.15(B)(16) as modified by Table 310.15(B)(6)
But, if and only if you meet the criteria specified (service conductors or feeder conductors carrying the entire load of exactly one residence (more properly "For individual dwelling units of one- family, two-family, and multifamily dwellings") then 310.15(B)(7) overrides the other tables.
That is all there is too it. If the values in (B)(16) had to be used, there would be no point in the existence of (B)(7).
Perhaps the inspector is claiming that the conditions for using (B)(7) are not met?
 
What type of cable are you installing ?
I can't claim proficiency with the new '14 approach on ampacity but it would seem that once you applied the allowances allowed by 310.15(B)(6), your cable would need that ampacity (unlike the old 310.15(B)(6) where the Code listed the wire size).
If your adjusted ampacity is 83 amps, or any number above 70, then the 60? limitations of NM (and perhaps SE) come into play.
 
augie47 said:
What type of cable are you installing ?
I can't claim proficiency with the new '14 approach on ampacity but it would seem that once you applied the allowances allowed by 310.15(B)(6), your cable would need that ampacity (unlike the old 310.15(B)(6) where the Code listed the wire size).
If your adjusted ampacity is 83 amps, or any number above 70, then the 60? limitations of NM (and perhaps SE) come into play.
Click to expand...


I think this gets a little tricky. What size service do you have for the dwelling. If you assume 100 amps which seems to be the smallest allowed then you would take 83% of the ampacity of a conductor after de-rating. Thus 100 amps means after de rating the conductor must be at least capable of 83 amps.

What is not clear is if you have a 100 amp service but only need 80 amps at the apartment and that conductor carries the entire load of the dwelling then you should be able to take 83% of 80 amps and feed that apartment with a conductor of 66 amps after derating. Not sure that is the intent
 
Dennis Alwon said:
I think this gets a little tricky. What size service do you have for the dwelling. If you assume 100 amps which seems to be the smallest allowed then you would take 83% of the ampacity of a conductor after de-rating. Thus 100 amps means after de rating the conductor must be at least capable of 83 amps.

What is not clear is if you have a 100 amp service but only need 80 amps at the apartment and that conductor carries the entire load of the dwelling then you should be able to take 83% of 80 amps and feed that apartment with a conductor of 66 amps after derating. Not sure that is the intent
Click to expand...

I'm shocked that this thread died with that comment :happyno:
The proper method of looking at the 83% is of significant importance. Surely someone else has input.
 
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