What size service is this ?

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Cletis

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If you run 3 overhead service conductors (500MCM,500MCM,250MCM) going to a 320/400 amp meterbase feedthru and then out to 2-200 amp 40 space panels with 2 sets of 4/0 SEU with a calculated load of 267 amps what would you call this service if an inspector asked you ?

A. 320 amp

B. 350 amp

C. 400 amp

D. Other
 
edward said:
C. 400Amp

The meter base is probably rated at 320A continuous.
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In that case I assume it would be 350A service. However, I don't know if there is a 350Amp rated service.

So I would go back to my original thought and say it is 400A.
 
The utility would charge you for a 400A service. 320 is just because it's rated at 80% of full load continuous. Meters are rated 320A, but it's still considered a 400. Dates back to the older style bolt in 400A services. Most have been replaced with a socket adapter that accepts a Class 320 meter, (although, between you and me, the socket dimensions of a Class 320 and a Class 200 are the same). A class 200 meter will fit just fine in a class 320 socket, but it will probably melt if run at 320A for very long. We put (CL320) stickers on all of our class 320 meter panels so a meter reader won't accidentally change out a 320 meter with a 200. Yes, it has happened. Yes, it will smoke. It does meter correctly, though, till it bursts into flame.:)
 
Cletis said:
If you run 3 overhead service conductors (500MCM,500MCM,250MCM) going to a 320/400 amp meterbase feedthru and then out to 2-200 amp 40 space panels with 2 sets of 4/0 SEU with a calculated load of 267 amps what would you call this service if an inspector asked you ?

A. 320 amp

B. 350 amp

C. 400 amp

D. Other
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D. Other: A violation of 230.90(A)

You have two 200 amp mains that exceed the rating of the aluminum 500KCMIL conductors which only have an ampacity of 310 amps, table 310.15(B)(6) (2008 and earlier or 310.15(B)(7) 2011 and later) would have let you use 400KCMIL copper or 600KCMIL aluminum for a dwelling 400 amp service but the 500KCMIL aluminum conductors are two small.

Are these utility supplied or owner supplied conductors? if utility supplied/installed then they follow the NESC requirements and not the NEC, it will depend upon the service point as to where you have to start following the the NEC.

In most cases this is at the weather head for over head service drop or the meter base for underground laterals.

In your post you said "If you run 3 overhead service conductors" which I took as meaning that you installed them but more info is needed for that to be determined.

If the overhead conductors are utility owned and the de-mark is at the weather head then just change the conductors in the riser pipe to 600KCMIL and you would be good to go.

Another issue is the requirement to group disconnects, since you are splitting the service into two 200 amp panels these must be grouped or a set of disconnects must be mounted next to each other by the meter (230.72) I have seen some who thought they could locate one panel in the garage and one in the basement but 230.72 would prevent this without additional disconnects

If these panels are use for two different buildings, then you can use 230.40 exception 3 to put double lugs in the bottom of the meter and run into the ground to the other building and into the other panel and treat it like a service which you would just follow the rules for a service without a meter at that location.
 
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If it's a residential service, I'd go with 350A under 2011 NEC and several earlier editions, per 310.15(B)(7). The 2014 edition allows the service conductors to have an 83% reduction in ampacity compared to the service rating... which figures out to 400A service rating after rounding up as permitted under 230.90(A) Exception No. 2.
 
I was thinking the same thing 256 amps.. so does the service size get its name from meterbase rating, service conductor rating to first disc or ocp rating of panels fed
 
Smart $ said:
If it's a residential service, I'd go with 350A under 2011 NEC and several earlier editions, per 310.15(B)(7). The 2014 edition allows the service conductors to have an 83% reduction in ampacity compared to the service rating... which figures out to 400A service rating after rounding up as permitted under 230.90(A) Exception No. 2.
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I just saw in the 2011 that exception #3 to 230.90(A) allows the combined ratting of the handles where two to 6 breakers are used as the disconnects to exceed the rating of the service conductors, it was even in my 1999 NEC so I must have forgot all about this exception:ashamed1:

disregard my previous post


So with the above known I change my post to C. 400 amps
 
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Smart $ said:
Disregard my reply to your earlier post. ;)

But wouldn't it only be rated 350A under 2011 NEC 310.15(B)(7)?
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I think it should be, but I think I remember somewhere that a circuits rating is based upon the breaker protecting the circuit, in this case two 200 amp mains?

Actually the 500KCMIL aluminum only has a rating of 310 amps so maybe a 300 amp service?
 
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hurk27 said:
I think it should be, but I think I remember somewhere that a circuits rating is based upon the breaker protecting the circuit, in this case two 200 amp mains?
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That'd be true for branch and feeder circuits. I don't recall any statement to that effect for services.

Actually the 500KCMIL aluminum only has a rating of 310 amps so maybe a 300 amp service?
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Non-main, non-dwelling, I agree.

Dwellings seems to be "excepted" under 310.15(B)(7), which permits 500kcmil aluminum on a 350A service [2011].
 
Smart $ said:
That'd be true for branch and feeder circuits. I don't recall any statement to that effect for services.


Non-main, non-dwelling, I agree.

Dwellings seems to be "excepted" under 310.15(B)(7), which permits 500kcmil aluminum on a 350A service [2011].
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If the conductors "you ran" were on the consumer side of the service point, that would be consistent with a 350A or smaller service.
If they are on the POCO side and POCO told you what size to run, it could just as easily be s 400A service, since they do not use the same conductor sizing rules.
 
Service size is the calculated 267 amps.

What the POCO calls it may be different - and likely will be in same classification as a full 400 amp service in most cases.

What the AHJ calls it for permit fees may also be different. This may very well be different in some AHJ's then others as well. Here there is a set permit fee for 0-100 amps, one for 101-200, one for 201-400, and I'd have to verify the higher figures, but it is in similar blocks of ampacity. So if done here, the OP's application would fall in the 201-400 and would be the same fee for any service value in the range.
 
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