# Table 310.15 B 7



## Gamit (Dec 30, 2009)

Today I failed a job because my feeder to my 100 amp sub panel was #2 AL . Inspector said I needed to change breaker to 90 amp? I understand that this table is no longer in current code cycle but can someone explain the new 83 percent deal ?


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## HackWork (Oct 2, 2009)

Gamit said:


> Today I failed a job because my feeder to my 100 amp sub panel was #2 AL . Inspector said I needed to change breaker to 90 amp? I understand that this table is no longer in current code cycle but can someone explain the new 83 percent deal ?


Whether you use the old table or the new 83% thing, it is only when the service/feeder is powering the entire dwelling unit.

So either the whole house or the entire apartment in a multi-family dwelling.

Adding a subpanel in a house that is only powering a portion of the house won't work.


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## CoolWill (Jan 5, 2019)

The old table is now in the Annex. The 83% still works out the same as the table. A table was just too easy to follow, so they mucked it up to make themselves feel smart.


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## Gamit (Dec 30, 2009)

HackWork said:


> Gamit said:
> 
> 
> > Today I failed a job because my feeder to my 100 amp sub panel was #2 AL . Inspector said I needed to change breaker to 90 amp? I understand that this table is no longer in current code cycle but can someone explain the new 83 percent deal ?
> ...


So are we saying thar feeders to sub panels does not qualify


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## CoolWill (Jan 5, 2019)

Gamit said:


> So are we saying thar feeders to sub panels does not qualify



Unless that subpanel carries the entire load of the dwelling, it has to be a full sized feeder.


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## Gamit (Dec 30, 2009)

CoolWill said:


> Gamit said:
> 
> 
> > So are we saying thar feeders to sub panels does not qualify
> ...


Understood thanks for clarification


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## Wiresmith (Feb 9, 2013)

CoolWill said:


> Unless that subpanel carries the entire load of the dwelling, it has to be a full sized feeder.



310.15(B)(7)


> (3) In no case shall a feeder for an individual dwelling unit be required to have an ampacity greater than that specified in 310.15(B)(7)(1) or (2).


if your service and main feeder are also 100 amp, then you could qualify

before you say, "when would that ever be the case?"

consider this, at the service point you have a meter main with two breakers in it, one 20amp that feeds a small single branch circuit and the other breaker is a 100 amp feeder (two breakers at the meter main). the small branch circuit could be something like a receptacle and light.

if (3) didn't exist in the scenario i described you would always have to use the larger wire. which would be larger than its upstream service counterpart, just because it doesn't feed the "entire associated load".


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## Wiresmith (Feb 9, 2013)

Gamit said:


> Today I failed a job because my feeder to my 100 amp sub panel was #2 AL . Inspector said I needed to change breaker to 90 amp? I understand that this table is no longer in current code cycle but can someone explain the new 83 percent deal ?


it depends, you didn't provide enough information, what size is your main feeder and service?


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## manchestersparky (Mar 25, 2007)

CoolWill said:


> The old table is now in the Annex. The 83% still works out the same as the table. A table was just too easy to follow, so they mucked it up to make themselves feel smart.


I made a copy of the table and taped into my code book where it used to be


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## Wiresmith (Feb 9, 2013)

Also, if you can use table 310.15(b)(2)(a), if say your ambient temp is 77f or less, like if it is in a conditioned space or deep enough in the ground(55f). Then your #2 al 75c is good for 94.5 and with 240.4(b) you can round your ocpd up to 100, all without 310.15(b)(7)

Although my personal reccomendation is never using the 240.4(b) allowance, but that wasn't your question


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