Question on fault current

[KWH]

I recieved the fault current from the poco which came in around 8800. The approved drawings have a note stating the service equipment shall equal or exceed this number which is common knowledge but there is another conflicting note that states the equipment shall carry a minimum of 22k rating. I was wondering if there is a reason to list a minimum. I would like to order gear with a 10k rating just second guessing over this. This is a gas station
3 phase 120/208 600amp overhead

 

[wirenut1980]

If the specs say 22k minimum, you better do 22k or ask for a clarification. Not sure why that is specified, but it does not really matter if that is what the customer wants. Are you bidding or installing at this point?

 

[KWH]

Fault Current

Fault Current

I am installing just looking to save some money.

 

[skeshesh]

Send a RFI (or RFC or whatever you call it in your neck of the wood) to the engineer and attach the utility info stating the available fault. You should be able to use 10KAIC if the information is correct and there's nothing unusual going on with the system.

 

[dkidd]

shall equal or exceed this number
but there is another conflicting note

The note is not conflicting. It says that 22k is the minimum, but it must exceed the available. What if available was 42k?

The 22k requirement is good conservative design that takes into account that the utility may make future changes that would increase the available fault.

 

[ron]

Some people feel that 10kAIC rated equipment is residential grade.

 

[jim dungar]

Some people feel that 10kAIC rated equipment is residential grade.

Not in Wisconsin. Our major POCOs have had a design level of 22kA since the mid 80's

 

[MarkyMarkNC]

I believe a lot of engineers cut and past a 22K requirement into any new construction equipment, without actually researching the actual available fault current, just to CYA.

This is a good example of a situation where it would definitely be worth the time and energy of getting the engineer to put his blessing on the lower AIC rating. Those 22K switched neutral breakers are ridiculously expensive.

 

[Knightryder12]

In my neck of the woods and as an electrical designer, when we call the POCO for the available fault current at the transformers bushings, they tend to give us the next size up transformer to account for any "future" upgrades. So that is probably why the engineer is requiring the 22K aic minimum.

 

[jim dungar]

This sounds like a situation where 'series-rated' equipment may be worthwhile.