400/320 whats next?

[e57]

Alright we all know the 400/320 class - what comes after that? Is it all 80% for continuous/non-continuous ratings?

400/320
600/480
800/640

You say why do I ask? An Engineer on my project called for an 800A Wye because (she said so ) we were over 480? ( I think she said...)

120/208/3?
KW-A
Total connected load
295-827.46
Demand load
174.1-488.34
Demand load (factored)
141.4-396.62

 

[jim dungar]

This is a POCO consideration, not an NEC "80%" issue.

The 400/320 has to do with using a self contained meter socket versus a CT cabinet.

Because many utilities do not consider residential ,and some commercial, services to be "fully loaded" they like to use a 320A self contained meter. But when you get to most 400A commercial services, which often operate closer to full load, the utilities usually prefer using CT's for metering. Above a 400A service metering is always done with CT's.

 

[e57]

The question is not really about CT cabs - More about the engineering of looking at demand factors over a certain point, and going for a larger service that is still under a certain point. i.e. my demand is still under 600A, but the engineer spec'ed and 800A because it was over 4~~ somthing.....

Was assuming that it has to do with the continuous vs non-continuous??? Like say a 400/320 does. Aware that the 400/320 is a "class" of service - wondering if there were others?

 

[jim dungar]

A 400/320A meter/service, is not really about continuous vs non-continuous. It is about how utilities apply their demand factors.

You need to follow the NEC method of applying/determining demand. The lowest number you gave was 396.62A so, in my opinion, a 400A service should not even be considered. The next value you listed was 488.34. If this is your load and no growth is expected, it is not unreasonable to use a 1.25 multiplier and say that you need a 610A minimum service. But, if the install cost was an issue, and depending what previous assumptions were made, you may be able make a case that 600A is sufficient.

This is definitely only a design issue and hinges on what values where considered in the calculations.

 

[e57]

It is about how utilities apply their demand factors.

You need to follow the NEC method of applying/determining demand. The lowest number you gave was 396.62A so, in my opinion, a 400A service should not even be considered. The next value you listed was 488.34. If this is your load and no growth is expected, it is not unreasonable to use a 1.25 multiplier and say that you need a 610A minimum service. But, if the install cost was an issue, and depending what previous assumptions were made, you may be able make a case that 600A is sufficient.

This is definitely only a design issue and hinges on what values where considered in the calculations.

Then that's the question - how are these demands applied? Obviously you don't (nor do I) see it as an NEC issue - but whats the next sizes up from your typical 400/320? (if taking that type of 'spread' into account?)

Otherwise design and money are in constant flux - and technically no issue.

 

[jim dungar]

For the values you posted typical utility services are: 320 (using a self contained meter) then the even numbers of 400, 600, and 800A (using fully rated CT's).

Each utility has their own method of determining service size based on the type of facility and the size of the service you request. You need to talk to you POCO to see how they do it.