smkie

So a guy i know and I were debating back and forth of on the size wire for a 100 A sp i told him you have to you use the 75 celsius colum on 310.16 which would be 3 AWG copper or a 1 AWG, he said " i could use 310.15(B)(6) which is would be 2 AWG alum. or 4 AWG copper. Who is right?

BEAMEUP

Your both right, If it was for anything other than a dwelling , you are right, If it is for a dwelling he is right.

electricmanscott

This is not correct....

310.15 B 6 Applies ONLY IF the feeder is supplying the load to the entire dwelling. Otherwise there are other factors that come into play.

I don't quite understand why this one is so difficult but it sure seems that it is. Probably a top 10 violation I see on a regular basis. In fact on job I am working on now the last guy in, just a few months ago, incorrectly used 310.15 B 6 to size a panel feeder. I will be pointing this out when I have the inspector in for my work.

BEAMEUP

Show me in the code book the word ENTIRE.

electricmanscott

Since I did not quote the section the actual word entire may not be there. I suggest you read 310.15 B 6. You'll see it says "all loads". That IS a direct quote. You can not use that table to size a "sub panel" No sub panel isn't in their either.

John Valdes

310.15 does say feeders and services. But if I used 310.15 to size wire for a sub panel I would be re-pulling the feeder.
Great question, and I look forward to hearing from the others, as I always use 310.16 for subs.

electricmanscott

Did you read what it says? Does anybody read what it says?

Dennis Alwon

You are correct in that the word "entire" is not there, however Scott is saying that the feeder must be the main power feeder in order to use 310.15(B)(6).

It goes on to state...

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BEAMEUP

After re-reading that section I can see both sides of the argument. Let me give an example of my thinking. Lets say you have a 400 amp service for a single family home, the service is on the side of the house by the garage. I have one run out of the meter to a 200 amp MB panel in the garage. The other run out of the meter goes into a 200amp disconnect next to the MB panel. Out of the disconnet I run 4/0 SER AL to a 200 amp sub panel on the 2nd floor.

In this case I can use 310.15 (b)6 to size the feeder to the sub panel on the 2nd floor. It does not serve the entire load of the house. There is a new sentence in this section that states "that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit."

Now lets go one step futher, I run a 100amp sub panel off the 200 amp sub panel on the 2nd floor, I can still use 310.15 (b)6 to size that run of SER as well.

That sentence I quoted in this post says circuits or feeders, not a single circuit or a single feeder, it plurl as in mutible as long as it is associated with that home I'm code compliant.

NolaTigaBait

THis is such a stupid rule. #4 is ok if its the main power feeder, but if you run a 2nd panel off that main feed, I need to use #3....Doesn't make much sense to me.

Dennis Alwon

[quote=BEAMEUP;195127]
In this case I can use 310.15 (b)6 to size the feeder to the sub panel on the 2nd floor. It does not serve the entire load of the house.] I agree but only because the garage is not part of the dwelling.

I totally disagree with this and IMO, there is nothing in that article to support this claim.

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Speedy Petey

I 100% agree, and have YET to hear ANY valid argument against it.

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Time flies when you're goin' fast.

Speedy Petey

Now WHY would you do this??? Will you feel better after reporting this "serious" violation?

IMO is it NOT a violation as this section is not as cut and dry as you make it out to be. This is QUITE open to interpretation, as many of the posts here show.

I have always used 310.15(B)(6) for sub feeders in a dwelling and will continue to do so.

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Time flies when you're goin' fast.

NolaTigaBait

Me too. Glad to hear I'm not alone on this!

BEAMEUP

Well weather I'm right or wrong, I have never been called on this in the state of Washington and have had this very example go thru plan review and get signed off. Now it can be likely that the inspectors in the state of Washington and all of the places I have done this are miss understanding the code, but the inspectors are passing it this way. So who knows. I have been wrong before & I guarantee that I'll be wrong again, but it's passing inspections

BuzzKill

yeah thast would be the wis thing to do I think

B4T

These CMP guys need to slow down making code changes and try using it in the real world like the rest of us.

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There comes a time when people who volunteer their service need to step back and see if it is better for them to retire. A red flag is when they become "cranky" and lose all sense of reality by making decisions that really don't make any sense..

jwjrw

In 2008 you now have to use the 60 column with SER cable here so you couldn't use 4/0.

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The more I learn the less I seem to know......

Dennis Alwon

Pete the argument is this. The reason we are allowed to use T.310.15(B)(6) for dwellings is because of the diversity of the loads in a residence. When you add sub panels you are changing the diversity of the load. For instance, if the sub panel only had loads for heating, a/c, etc then the diversity that exists for dwellings is no longer there.

In reality, I agree with you that problems will probably never arise from this and perhaps it should be re written. I am not arguing that at all but I agree with Scotts interpretation of the rule as written.

There now you have the reason for the rule- it will not change anything for you but at least you know why. For me, I prefer to wire it by the code to keep my ass out of potential problems.

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waco

I fail to see the issue. Paragraph 310.15 (B) (6) isn't very well written, but the part that says, "...that supplies, either by branch circuits or by feeders, or both, all loads that are part or associated with the dwelling unit" only serves to confirm the applicability of Table 310(B)(6) which would appear to be "dwellings" without reservation or exception.