Available Fault Current

[Jim10]

This may be a stupid question, but here goes anyway...
We have a site where a 4 gang meter bank was installed with 200A mains for each, rated for 22kAic. The POCO has come back and said the available fault current at point of delivery is 22,025. The city has said they will allow the power install if an engineer signs off on it. Is that minor difference enough to require increasing the kAic rating of the bank and mains or is it small enough to be a safe install? I can also try to reach out to the POCO to get info to do a more complete fault current calculation if infinite bus was used if need be.

*DISCLAIMER this is the first of my involvement in this project haha*

Thanks

 

[RD35]

I would bet the POCO used infinite bus in their calc. Sure would be nice if they would help you out and figure losses back to (at least) the first sub. I've had to do that in the past on a job or two. Usually not a big difference, but in this particular case it would very likely fix your issue.

 

[Dennis Alwon]

Jim, I have heard that it is not uncommon for the power company to have more than 10,000 aic in residential areas. This certainly can be an issue but nobody seems to say anything about it. Is it dangerous? I suspect it can be but let the engineer types answer this one.

 

[kwired]

This may be a stupid question, but here goes anyway...
We have a site where a 4 gang meter bank was installed with 200A mains for each, rated for 22kAic. The POCO has come back and said the available fault current at point of delivery is 22,025. The city has said they will allow the power install if an engineer signs off on it. Is that minor difference enough to require increasing the kAic rating of the bank and mains or is it small enough to be a safe install? I can also try to reach out to the POCO to get info to do a more complete fault current calculation if infinite bus was used if need be.

*DISCLAIMER this is the first of my involvement in this project haha*

Thanks

Where is point of delivery in relation to the meter bank in question? If there is any conductor between those two points, you will have reduction and it won't take much to reduce by only 25 amps. If the meter bank is the point of delivery, kind of sort of a problem, though the number given may be worst case and the real figure might be less - that is where the engineer really comes in.

 

[Jim10]

According to their standards doc, point of delivery is at the meter bank which is the issue. I have a line out to the POCO rep now to verify that and to try to get more information.

 

[topgone]

According to their standards doc, point of delivery is at the meter bank which is the issue. I have a line out to the POCO rep now to verify that and to try to get more information.

That's a normal thing! The POCO will tell you the available fault current at a certain point of connection. It's up to you to calculate and determine the prospective fault current the will be. by virtue of the service line length and size.

 

[Julius Right]

If the POCO transformer is 2500 kVA 480 V [5.75% impedance ANSI C37.010]

and 133 ft. cable of 3*350 MCM copper conductor the short-circuit current will be 21.925 kA. [the System short-circuit power infinite].

If the POCO medium voltage system short-circuit power is 500 MVA [see IEC 600076-5 Table 2 up to 24 kV system] then at 125 ft. cable length Isc=21.893 kA