310.15(B)(7)(3)

[LarryFine]

I don't think anyone is arguing that but where does it allow a feeder, in augies 100 amp example, #2 Al to be used at 100 amp ampacity unless it carries the full load

In my opinion, 310.15(B)(7)(3) does.

It may not say "100 amps" (or specify an ampacity) but it does effectively say it only needs to match the qualifying SECs.

 

[LarryFine]

Get the torches and pitch forks ready, but I’ ll disagree. If a feeder does not supply the entire load, all bets are off. I interpret it this way because why include this language of supplying the entire load. It either does or it doesn’t.?

Then, why include what 310.15(B)(7)(3) says?

 

[LarryFine]

The language in (B)(7)(3) very clearly permits that. Nothing in (3) talks about the feeder carrying the full load. (3) applies in all cases.

Exactamundo.

 

[LarryFine]

Yes sir , thats the way it could be interpreted ......... but 2020 NEC refers us to 310.12(C), then back to 310.12(A)&((B), and the only way you get to apply the 83% reduction, is if the service or feeder supplies the entire load? If not the entire load, no reduction?.

This is, in my opinion, a separate situation. The downstream feeder has already been sized to carry all or less of that 83%.

If the SECs are properly sized with that allowance, the feeder is considered properly protected by that same allowance.

It doesn't matter if the feeder carries 100% of that 83% or a lesser portion of it. It can never be subject to more current.

 

[Greentagger]

Then, why include what 310.15(B)(7)(3) says?

Agreed. Why?
Why also include the whole entire load thingamagiggy when it refers you back to 310.15(B)(7)(1)&(2). Definitely could use some better wording here.

 

[LarryFine]

Agreed. Why?

I meant "Why else?" To me, the intent is clear.

There are other code sections that are "overridden" by blanket permissions and exceptions.

 

[Greentagger]

Check out the graphic in 2020 Handbook 310.1

 

[LarryFine]

Check out the graphic in 2020 Handbook 310.1

Can you possibly post it or a link?

 

[Greentagger]

No sir, sorry. Don’t have the technology. My kids are already moved out.

 

[Greentagger]

Oh , and the Wife isn’t home yet.

 

[LarryFine]

Let me throw this into the discussion:

When it mentions a feeder carrying "the entire load," I believe it means as opposed to having more than one feeder, say where someone decided to wire a house with a sub-panel on each floor. If you had, say, a 200a outside panel with two or three 100a feeder breakers, clearly each feeder would have to be fully rated for 100 amps.

Unless, of course, the main panel only had a 100a main breaker, and #2 al was deemed suitable using the 83% allowance.

 

[texie]

I'm surprised there is so much discussion on this. There is no doubt that the feeder can use the 83% rule in this case. It should be obvious that one would not need a feeder larger that the SECs suppling it. The rule is very clear.

 

[LarryFine]

I'm surprised there is so much discussion on this.

In this forum? I'm not. It often seems the simpler the topic, the deeper the discussion.

 

[augie47]

erased