#2 AL feeders

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MrHopper

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I have a question for someone with an answer. We've run into a bit of a problem. We ran alot of #2AL XHHW-2 to some storage units. Each unit has its own 100A service single phase. These are feeders coming out of a meter bank. Each feeder is piped individually with 2 hots, 1 neut, and 1 ground. They are direct buried for I would say 98% of their run. They then come above ground in pipe to an LB and into the building. We had each line protected with a two pole 100A Main breaker when leaving the meter bank.

Now, 310.16 shows #2AL XHHW-2 has a 90 deg rating and is rated at 100A, The 75 deg rating is 90A (thats 167deg F). The inspector says to go with the breaker rating of 75 deg(which is what I was thinking)

This is in Ohio, the temp goes from 0 deg F, to 100 deg F. Probably average would be around 60 deg F. I think there would be a correction factor that could be used to get this over 90A in the 75 deg column being the Ohio never sees 167 deg F. The inspector says in the sun it can go past that temp and overheat the breaker. But we're talking about the wire, not the breaker. Anyway, I would like to find a correction factor that would allow me to use 240.4B.

Pretty much the inspector wasn't convinced either way so he got another inspectors opinion, then they both weren't sure what to think about it so after about 30min of debate he wanted to error on the side of caution and recomend using a smaller size breaker.

The owner says no way, he wants 100A breakers. Any advice? Thanks
BTW, I do recall something about I think it was service wires being able to run something like 125% their rated ampacity. Is there something like that or was I dreaming that, and if there is such a code would it apply to feeders? Thanks again
 
MrHopper said:
Now, 310.16 shows #2AL XHHW-2 has a 90 deg rating and is rated at 100A, The 75 deg rating is 90A (thats 167deg F). The inspector says to go with the breaker rating of 75 deg(which is what I was thinking)
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If you look at the bottom of 310.16 you will see temperature correction factors.

They show a maximum factor of 1.05 that can be applied.

90 * 1.05 = 94.5 than roll up to the 100.

HOWEVER, I have never tried to roll up and the inspector would have to be convinced that the ambient temp would not exceed 77F.

It looks like 90 amp breakers or larger conductors.
 
I agree with Bob. If they never left the ground you could get up to the 100 amp CB but with a maximum ambient of 77 degrees you have to either drop down to 90 amps or pull in larger aluminum or # 3 copper conductors.
 
Is it the 75 degree terminations of the breaker that is limiting the ampacity of the wire here or not?

The following is most likely retarded but I was bored and vomited this up.

Do the terminations in meter boxes normally have a higher than 75d rating?
Do the terminations in the 100a main panels normally have a higher than 75d rating?(not the breaker terminals, but the lugs in the panel itself)

If so can he either:

Do away with the 100a main panel if these are not that large of storage units and the current sub panels are immediatly inside the walls and have 6 or fewer throws they would become the new mains?

Or

Move the 100 amp main panels over to each unit where the LB goes in? if you then have a compliant 100 amp service there is only the last few feet of wire to deal with.

let the beating begin....
 
termination

termination

guys, as I get older sometimes I don't comprehend as well, however, in this case I can't see ambient temp. as a realtive factor. 110-14 addresses terminations and if the breakers at the point of termination are 75 deg. rated, then, to me, the feeder will be protetced by a breaker not exceeding 90 amp.
 
MrHopper said:
They are direct buried for I would say 98% of their run.
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Did you try 310.15(A)(2), exception?

Anyway, I would like to find a correction factor that would allow me to use 240.4B.
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240.4(B) is of no use to you, the ampacity (and a standard OCPD size) is 90A.

You have to determine (to the AHJ's satisfaction) that all but 10' of that run is in an ambient temperature that will increase the ampacity to 100A. I believe this run might just qualify.

I hope you win this, and never repeat this mistake again. :D

In the meantime, figure your breakeven for the job, and figure out what the 90A discount will be for the mistake. What is the calculated load in these units? Is it even close to 90A?
 
MrHopper said:
This is in Ohio, the temp goes from 0 deg F, to 100 deg F. Probably average would be around 60 deg F. I think there would be a correction factor that could be used to get this over 90A in the 75 deg column being the Ohio never sees 167 deg F. The inspector says in the sun it can go past that temp and overheat the breaker. But we're talking about the wire, not the breaker. Anyway, I would like to find a correction factor that would allow me to use 240.4B.
Click to expand...

The 167?F max temp is not just a function of sun exposure or other ambient factors but also includes the heat generated from current flow. . When you combine sun with current you can get up to that temp. . If your lugs were rated for 90?C, the terminations could tolerate more than 167?F.

MrHopper said:
Pretty much the inspector wasn't convinced either way so he got another inspectors opinion, then they both weren't sure what to think about it so after about 30min of debate he wanted to error on the side of caution and recomend using a smaller size breaker.
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Hey Mr Hopper,
This is the second inspector that you talked to at the counter. . Bob [inspector #1] was looking for a way to keep you from losing your shirt on this job. . What we weren?t sure of was a way to rescue you from a commercial installation that was already completed according to the residential table [T310.15(B)(6)]. . I saw that he was spending a lot of time looking for an ?out? for you. . I would guess that it was about 30 minutes that Bob spent. . I couldn?t stick around longer than about 5 minutes because I had so many other things going on.

My suggestion is this:
Get the General Contractor to get the Engineer or Architect to revise the prints to show 100amp mains because they?re 60amp on the prints right now. . Don?t let the General squirm out of responsibility. . He had the job bid with prints that showed 60amp panels. . If he wants the 100amp, he needs to provide a print to us for plan review. . Bob can see to it that the plan review gets done in about 5 minutes. . The revision should show 100amp panels supplied by #2 and the prints should specify aluminum wire [110.5]. . Then call Bob and tell him you have your prints straighten out.

George gave you a solution [on this thread] that neither Bob nor I thought of. . You can use 310.15(A)(2)X. . Under the ground doesn?t get hotter than 77? and your above ground section is 10 feet or less, so you can use the multiplication factor of 1.05 to get your wire amps to 91 or higher. . Then your 100amp breakers are OK according to 240.4(B) + 240.6(A).

I know you are just getting into Commercial work and made the mistake of going to 310.15(B)(6) like you are used to doing for Residential. . But this isn?t the first Commercial job for that GC. . We accept NEC only inspections for residential projects but for commercial projects you always always must have approved prints and they must be available on the jobsite at the time of inspection. . Your inspection will be according to NEC and manufacturers specs, just like residential. . But for a Commercial project also according to approved prints and the GC knows that fact. . He knows you can?t get 100amp feeders past inspection when the prints say 60amp and now you know that too.

Apparently there is another building on this property that had this same installation in the past but didn?t get caught on inspection. . Sometimes we miss stuff. . If the GC thinks we approve stuff that varies from the prints purposefully, he?s wrong. . If he wants the 100amp feeders, that?s between him and his engineer/architect. . Don?t let him push this all off onto you.

David
 
David, very good post!

FWIW, My hat is off to you and the other inspector.

Roger
 
Thank you

Thank you

David, Thank you for your support and help. You could've said we screwed up and that is all there is to it. But you took the time to pull the prints and go through all this with me. You and Bob are really fantastic and we appreciate the 2 of you. Thanks for your reply. Mark
 
roger said:
David, very good post!

FWIW, My hat is off to you and the other inspector.

Roger
Click to expand...

My hat is off too!

What a pleasure to read your advice. I think you and Bob are a credit to your profession.


John
 
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