I am a electrical contractor from New Haven in a bind. I am installing a new 2500 Amp 120/208 Volt service on a job and the local utility(UI) is requiring me to show them that there will be no more than 10,000 AIC possible at their meters. My engineer and a second engineer I spoke with don't have the software to make the calculations. I am looking for someone licensed in Connecticut to take a look at this and preform this study to satisfy the local utilities requirements. If anyone is interested or know's of a person or company who can help me please let me know. Thanks for your help.

Was this also posted on Mike Holt's forum?

What you are asking for is a simple short circuit calculation to determine the amount of available short circuit current at your meter centers. I am surprised your engineers would not be able to do this. Almost every fuse manufacturer offers free software that is conservative enough for selecting AIC of breakers and SCCR of equipment. More robust software packages, like those from Easypower, SKM, and Etap, are be able to handle more complex circuits such as paralleled utility transformers.

Make sure you involve the utilities engineering department in your discussions.
I had a local contractor get into trouble simply because they asked for a service larger than they needed. Job specs called for a 600A 208V meter center series rated for 22kA, as required by the utility. The contractor got a good price on a 800A one, so, as a favor to the customer, he asked the utility to provide a service capable of being upgraded to 800A. The result was that now the utility required the meter center to be rated for 42kA.

Yes I did post in Mike Holt's forum looking for help. I was searching the web for answers when I came across this forum. I don't know what to say about my engineers neither one can give me an answer. One did the calculation on some simple software but came up short. He couldn't input a lot of the variables. So I'm just reaching out to any one who can put me in touch with some one who knows what needs to be done.

These guys can help

American Electrical Testing Co., Inc.
34 Clover Drive
South Windsor, CT 06074
Phone: (860) 648-1013
Fax: (781) 821-0771
E-mail: jpoulin@aetco.com
Web Site: http://www.99aetco.com
Primary Contact: Gerald Poulin

ok, maybe I am missing something here. If this is a 2500A 120/208V ckt would this not be an instrument transformer rated meter installation, at least CTs installed? Then the only direct connection would be voltage at 120/208V with, what? #12 wire?

The CTs would be donut CTs, so a short on the secondary side would do what? After all, you need to short CTs prior to opening the CT ckt, if energized? That leaves the potential wiring coming into the metering can. A #12 THHN conductor damage curve has it withstanding 200 A for 2 sec (IEEE 1584 cutoff) and 3 cycles it fails at 1400 A.

What is the size of the transformation feeding this 2500A service? Have you asked UI for their available fault current? Who owns the transformer, the utility or customer? It could be a fairly simple calculation to figure but I was just throwing out some random, common sense?? thoughts. Of course it has been a long trying day, so maybe everything I said should be ignored!!

The service is 2500A which feeds a distribution board (molded case breakers) which feeds several multi-meter centers.

So, if I understand correctly, there is a MCCB for each multimeter center?

Yes, but I am only going on the one-line the OP posted on a different forum.

it would be near impossible to have a 2500A service limited to 10K amps, even with current limiting fuses. You would have to have a lot or reactance, probably stand alone reactors.

What is the Z impedance on your transformer.

The other thought is to limit current on each meter branck with current limiting fuses or breakers.

Thanks for the help everyone. I called up the Guy that Zog recommended and he put me in touch with someone in New Jersey. He seams to know exactly what I need. So hopefully I will have this sorted out soon. As far as the meters being read off CT's, only the owners meter is on CT's. The 65 apartment meters are all on strait 120/208 Volt meters. The gentleman I spoke with recommended that I use a fused disconnect with current limiting fuses. Sounds like a good idea to me. So I sent him the info and he is going to do some calculations. I will keep you posted how it goes. Thanks again.