Fault current calculation

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monitaverma

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Hello
I am working on Multi-family units (Total 4 units). Currently, there is 200 amp incoming service outside the building and each unit is fed by 30 amps. 30 amp panel is in the hallway. They have also (1)60 amp House panel.

New electrical scope includes new 400 amp service. New 70 amp panel to each unit. Existing 30 panel will serve like a sub-panel to new 70 amp panel.

Plan checker asked me to submit KAIC rating for new distribution board. So I submitted Utility drawing, which says "Maximum fault current is 22KAIC". She asked me about existing 30 amp panel KAIC rating. She also told me that, new panel KAIC rating is 22KAIC and existing panel KAIC will be less, as it was installed like 15 years ago. How you going to protect existing panel?

Pleas give me some suggestion on this, as i really want to get it done.

Thanks
 
Bussmann.com has info on this topic available. Fault current calcs are usually the domain of the PE/EE....but within the capabilities of most EC's.
The 'point-to-point' system works well.
 
monitaverma said:
She also told me that, new panel KAIC rating is 22KAIC and existing panel KAIC will be less, as it was installed like 15 years ago. How you going to protect existing panel?

Pleas give me some suggestion on this, as I really want to get it done.

Thanks
Click to expand...

There is no way to predict the AIC rating of your existing breakers, age has nothing to do with it. You need to get the part number for all of your existing breakers and go back to the manufacturer for assistance.

FWIW, very very few UL Listed "loadcenter" breakers built since the early 70's are rated less than 10kAIC.
 
John Arendt said:
Bussmann.com has info on this topic available. Fault current calcs are usually the domain of the PE/EE....but within the capabilities of most EC's.
The 'point-to-point' system works well.
Click to expand...


excuse my ignorance but what is "point-to-point " system ?
 
jim dungar said:
There is no way to predict the AIC rating of your existing breakers, age has nothing to do with it. You need to get the part number for all of your existing breakers and go back to the manufacturer for assistance.

FWIW, very very few UL Listed "loadcenter" breakers built since the early 70's are rated less than 10kAIC.
Click to expand...


The fault current should be easy to get from the PO-CO around here it is PG&E and they will send you a "fault current letter".
If the 30 amp panels are only 15 years old they should have the KAIC listed right on the face and the panel should have it listed on the cover assuming it has not been worn off or painted over.
 
ARC:

"excuse my ignorance but what is "point-to-point " system ?"

It's not ignorance, only an unfamiliar term!
Just what it implies...
Start at the utility xfr secondary terminals, proceed to main disco/gear, proceed to sub-panels/discos, etc.

BTW, remember reading somewhere that branch cb's that have NO AIC markings are 5K. (FWIW)
 
by the time you figure all your wire lengths and sizes, I would not doubt the problem will be non-existant. It doesn't take much wire on a 70 amp circuit to drop the fault current considerably.
 
acrwc10 said:
If the 30 amp panels are only 15 years old they should have the KAIC listed right on the face and the panel should have it listed on the cover assuming it has not been worn off or painted over.
Click to expand...

You don't care about the SCCR of the panel any where near as much as you do about the AIC of the installed breakers. It is very common for replacement breakers to be installed without regard to the system SCA rating.

When it comes to fault currents there are lots of acronyms the commonly accepted ones are:

AIC - Amps Interrupting Capacity, applies only to devices intended to open fault currents like fuses and breakers, often given in thousands of amps so seeing kAIC is not uncommon but most engineer would say "the AIC is 22k".

AIR - Amps Interrupting Rating, similar to AIC

SCA - Short Circuit Amps - not extremely definitive but usually used to indicate the available fault current

SCCR - Short Circuit Current Rating - the amount of fault current a piece of equipment can handle failure, applies to devices not intended to open during faults like non-fused switches, panels, and machines.

Withstand Rating - okay not an acronym, this term has effectively been replaced by SCCR
 
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