# 240.4 (B) (2) : Is a Sub-Panel Feeder 'not part of a branch'?



## onilozay (Jun 16, 2013)

Hello and happy T-Day

Ok, I know the difference between feeders & branches but...

I've got a question related to 240.4 (B), specifically 240.4 (B) (2). In this section it mentions you can use 'next standard overcurrent device rating' if all 3 conditions of 240.4 (B) are met.

My case is I'm feeding a Sub-Panel which carries 1 story of a houses load. It has a 2 THWN wire (115A @ 75deg).

-(1) Its under 800A, check
-(3) It doesn't correspond to standard size breaker, check

-(2)But, even though its not a branch circuit, it feeds an entire panel, so its not exactly a dedicated circuit.

Bottom line, from code perspective, can I use a 125A breaker on this, next size up?

Thanks all and enjoy the holiday!


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## Black Dog (Oct 16, 2011)

onilozay said:


> Hello and happy T-Day
> 
> Ok, I know the difference between feeders & branches but...
> 
> ...


Yes you can, look at the table 310.15(B)(7) in the 2011 NEC


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## macmikeman (Jan 23, 2007)

Black Dog said:


> Yes you can, look at the table 310.15(B)(7) in the 2011 NEC


Not so sure about that one Harry, sounds to me like it carries *one story* of a house, (meaning possibly another story to the story) in which case that feeder will not be supplying the *entire load *to the dwelling and will not qualify for that exception.


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## Dennis Alwon (May 9, 2009)

Few questions. If this wire is nm cable then you cannot use the 75C column so you would be limited to 100 amps on #2 copper unless it carried the entire load of the dwelling as Mac pointed out.

Table 310.15(B)(7) does allow #2 at 125 amps but it does not sound like the OP is asking about this.

BTW 2014 has done away with that Table. If you want 125 amps then you would take 83% OF 125 AMPS= 103.75 AMPs , that means you would need a conductor that is good for that amperage and then it can be used for 125 amps.-- Again this is for the entire load of the dwelling

If you want to use 240.4(B) can be used for a feeder but the calculated load must be less than the actual ampacity of the conductor. For example, a 6/3 nm run to a sub panel where the calculated load is 55 amps or less (amp of #6 at 60C) then you can install it on a 60 amp overcurrent protective device.


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## onilozay (Jun 16, 2013)

Thanks for the responses so fast! This makes sense now. I guess I'm limited to 100A, which will work fine. My load is under this.

Yes, this feeder does not feed the entire house, but just 1 floor out of 3. And looking at the definition of the old table T310.15(B)(7) I can see it does not fit the criteria of a "main feeder".

Also, Most of the feeder run is in EMT using THWN, but there is a 15' section that is in NM 2-3. So even if it did feed the whole house, there is the weak link.

Thanks!


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## Awg-Dawg (Jan 23, 2007)

Dennis Alwon said:


> If you want 125 amps then you would take 83% OF 125 AMPS= 103.75 AMPs



I dont see alot of this, so where did the 83% come from?


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## onilozay (Jun 16, 2013)

Hi Awg-Dawg,

They eliminated table the NEC 2011 T310.15(B)(7) in the new 2014 NEC. In its place we are told to use the figure of 83% of the entire load supplied to dwelling unit in section 310.15(B)(7)(1) of 2014 NEC to choose wire ampacity


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## onilozay (Jun 16, 2013)

Oops, I meant 83% of the *service rating* not load of dwelling unit. Correction.


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