waco

Was talking to an inspector about changing a 100 amp service to get rid of a Federal Pacific panel and too much service cable in the structure. I said I would use 2-2-2-4 SER feeding a main lug panel from an outside main. He showed me something in the code (I don't know what version) indicating #2 AL was too small for 100 amp service feed.

But, my 2008 NEC, Table 310.15(B)(6) shows #2 AL for 100 amp, but includes the caveat, "three wire."

I've made myself half blind trying to find the place in my codebook that he showed me in his codebook which (as I recall) limited #2 to 95 amps.

Man, I sure don't want to get sideways with the inspector. Think I should just go ahead and use 1-1-1-4?

Problem is, I've always used 2-2-2-4 for sub-feeds on 100 amp services!

Magnettica

Have to agree with the inspector here.

Table 310.16 (B)(6) does say 120/ 240 volt 3-wire.

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InPhase277

What he showed you was table 310.16, in the aluminum column on the right. #2 aluminum in the 75C column is rated at 90 A.

310.16(B)(6) applies to the wiring between the meter and the first overcurrent device. And some may even interpret it for use on 3-wire feeders to detached buildings pre-2008 Code.

augie47

If you are under the '08 Code, he ,may be referring to 338.10(B)(4) which limits interior SE cable installs to 60° rating (#2 @ 75 amps).
There is a lot of controversy as to 338.10 taking precedence over 310.15(B)(6), but some inspectors enforce the 60°.

Jim Port

Wouldn't that just be the description of the service characteristics? How would you describe a 120/240 single phase system? Ie this would not apply to a 277/480 service or a 120/208.

Dennis Alwon

IMO if the se cable carries the entire load of the dwelling then T. 310.15(B)(6) applies. Read art. 310.15(B)(6) .

The 3 wire refers to the service as mentioned above by Jim.
Gus brought up 338.10(B)(4) but I disagree with him on that. That's another story but your inspector may be using that also.

I don't see anywhere in the code where 2 aluminum is rated 95 amps. #2 copper SEU at 60C would be but I think you are using alum.

Magnettica

No, of course a 120/ 208 service wouldn't apply because A) code specifically says 120/ 240, and B) because how many houses do you know of that have 480 volt services?

I just read the article, not the table, and it appears that I was wrong and so is the inspector. The article specifically allows the feeders as described in 310.15 (B)(6) with or without an EGC to be sized to Table 310.15 (B)(6).

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John Valdes

I agree. But. What the hell is 310.16 for? 310.15 (b)(6) indicates services and feeders.

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If your not getting old, you're dead.
Tom Petty

Dennis Alwon

John, I don't understand your question? 310.16 is for everything other than dwellings as mention in the Table. Not all feeders can use 310.15(B)(6). They must carry the entire dwelling load to be use that table.

Jim Port

The whole sizing debate of 310.16 vs 310.15B still does not make sense to me when I can run a smaller cable size if it carries the full load of the house than if it only carries a portion of the load.

Dennis Alwon

It is definitely a weird article and not well written.

If you have a 200 amp panel outside as service equipment that has feed thru lugs then I can run 2/0 copper to an interior panel that serves all the loads of a house. Now if I add an a/c circuit to that outdoor panel and take away some of the load of the house then I must use 3/0 copper.

This will obviously be challenged again for the 2011 and will no doubt still be unclear. There was some talk of allowing an a/c or a remote garage to be fed from the panel and still be able to use 310.15(B)(6). We will see how it plays out.

Magnettica

You got that right! For the most part that's all I do is old work residential so I use the 310.15 (B)(6) table all the time. It wasn't uncommon to see 2/0 cu used for 200 amp services at this old commercial building where the company I used to work for did work all the time.

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waco

I'm guessing the conclusion is to use 1-1-1-3 and stay okay with the inspector, but I still don't see the reasoning. However, the cost is similar and 1-1-1-3 is available.

I don't know, just about the time a guy can settle into a routine, somebody changes the rules. I read elsewhere that the change was made because of the temperature ratings of the lugs. I'm thinking THHN wire that is running at 194 degrees F (Table 310.16) is serving a dwelling that is on its way to burning down.

NolaTigaBait

Yeah, don't want to piss the inspector off. I've come across this stuff before. Had an inspector tell me the ground rods could NOT be m ore than 6 feet apart. When I install a 100 amp feeder thats the size I use. The chart says for Feeders as well. Like Dennis says, if its the main feed, then no prob using the #2.

frenchelectrican

Nola .,,

Let me underline that part I think you may mis type this one it should be not less than 6 feet(1.8m) apart if I read it right.

Merci,Marc

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Pas de problème,il marche n'est-ce pas?"(No problem, it works doesn't it?)

waco

Somebody suggested using a 90 amp breaker to get past the inspector, then swapping it for a 100 amp. Think I'll use 1-1-1-3 and walk away from it.

Dennis Alwon

marc I think the inspector was telling him the rods needed to be closer than 6" apart. The inspector is incorrect.

NolaTigaBait

What's the $$$$ difference?

NolaTigaBait

Right Dennis. This one is a little more black and white than the 310,15b6, but still.

Dennis Alwon

That's what I would do, and leave the 90i amp breaker f this isn't the entire load of the house. A service for a dwelling cannot ne less than 100 amps but the sub panel certainly can be.