KAIC

mannyb

Senior Member
If I have an exisitng 200a 240v 3 ph 65kaic panel and I wanted to add a 100a subpanel off the 200a do i need to stay at 65Kaic or better or can I go down 22kaic.
 

engineerintraining12

Senior Member
Location
Saint Louis
The rating of the 100 amp subpanel downstream is dependent on the available fault current at the panels location. The feeder size/distance to the subpanel would play a roll in what your available fault current might be at its location. If your sub panel is close to the main panel, I would probably keep the rating at 65KAIC because you don't have a lot of resistance from the short distance the feeder runs. ( This is assuming that the original 65KAIC rating for the main panel is accurate ). If the subpanel is farther away, you would need to calculate what the available fault current is at its location. ( This is dependent on utility transformer size / impedance and feeder distances and sizes all the way to your sub panel location. )
 
Last edited:

Carultch

Senior Member
Location
Massachusetts
If I have an exisitng 200a 240v 3 ph 65kaic panel and I wanted to add a 100a subpanel off the 200a do i need to stay at 65Kaic or better or can I go down 22kaic.
The 65 kaic rating could be in excess of what was needed when it was originally built. If the available fault current at the existing panel is much less than 65 kA, your KAIC rating only has to be as large as necessary for the fault current at the location of the panel. The fact that it is 65 KAIC doesn't mean your components need to match it.

Fault current at a transformer secondary, worst case scenario, is amps associated with the KVA rating divided by impedance as a decimal. After a feeder length, it also depends on the impedance of the conductor paths to the location in question, that depends on length, size, conductor material, and raceway magnetic properties if applicable. Explore a fault current calculator, or short circuit current calculator, to get a realistic value.

One way to get around this, is to take credit for equipment combinations with listed series ratings. Some breakers are rated together as a series combination, so that the upstream breaker can protect the downstream breaker, even if the available fault current at the downstream breaker exceeds its own rating. It is also common that certain breaker models are listed for series-rating in combination with certain fuse classes, such that the upstream fuse protects the downstream breaker. This allows for reduction of the KAIC rating of the subpanel breakers. Again, it has to be a specific combination that is listed as series rated and documented by the breaker manufacturer, in order for the breaker to be used where it otherwise would need a higher KAIC rating..
 

petersonra

Senior Member
Location
Northern illinois
Occupation
engineer
Don't forget if you try to apply a series rating you need to look at potential motor contribution. Most everything I do has enough motors in it that a series rated combination just doesn't work.
 
If I have an exisitng 200a 240v 3 ph 65kaic panel and I wanted to add a 100a subpanel off the 200a do i need to stay at 65Kaic or better or can I go down 22kaic.
I would like to make a few points.

First, one thing we would need to know is more specifics about what "65 kaic panel" means. The panelboard itself has a SCCR rating, while the breakers have an AIC rating. In practice, a panel board will likely have a SCCR as high or higher than the AIC of the highest rated breaker that can go in it, so this is mostly academic I believe. Are all the branches 65k? It's quite rare to have 65k branches because of series ratings - but I guess fully rated systems become more common in industrial settings or where there is motor contribution as petersonra mentioned.

It's hard to know without some digging if the 65k is actually needed. It seems a fair number of people use 65k mains because they don't know how or are unwilling to investigate the available fault current. Or perhaps they just want to be covered for future expansion. 65k branches are rare in my world, and expensive* too, so it seems unlikely someone would use them Willy nilly.
 

mannyb

Senior Member
I would like to make a few points.

First, one thing we would need to know is more specifics about what "65 kaic panel" means. The panelboard itself has a SCCR rating, while the breakers have an AIC rating. In practice, a panel board will likely have a SCCR as high or higher than the AIC of the highest rated breaker that can go in it, so this is mostly academic I believe. Are all the branches 65k? It's quite rare to have 65k branches because of series ratings - but I guess fully rated systems become more common in industrial settings or where there is motor contribution as petersonra mentioned.

It's hard to know without some digging if the 65k is actually needed. It seems a fair number of people use 65k mains because they don't know how or are unwilling to investigate the available fault current. Or perhaps they just want to be covered for future expansion. 65k branches are rare in my world, and expensive* too, so it seems unlikely someone would use them Willy nilly.
Thank you for reply, You are The MDP is a GE 800a with 3- 200a GE panel series AQF type these panels are 65kAIC and 1-100a GE type AQF panel 65kaic rating . The drawings indicate that the new subpanel will extend off the 100a and match name and KAIC rating. There is no added load. They are just relocating circuits to isolate equipment breaker to one panel, I dont know why but that the long and short of story. If this was not the case, how would one proceed to add a sub panel and keep series rated? Would I keep AIC from breaker rating to new subpanel or keep the kaic from panel its feedting?
 
Thank you for reply, You are The MDP is a GE 800a with 3- 200a GE panel series AQF type these panels are 65kAIC and 1-100a GE type AQF panel 65kaic rating . The drawings indicate that the new subpanel will extend off the 100a and match name and KAIC rating. There is no added load. They are just relocating circuits to isolate equipment breaker to one panel, I dont know why but that the long and short of story. If this was not the case, how would one proceed to add a sub panel and keep series rated? Would I keep AIC from breaker rating to new subpanel or keep the kaic from panel its feedting?
Many times you just don't have to worry about interrupting ratings in downstream equipment, due to series ratings. Of course the downstream equipment has to have a series rating with the upstream equipment, but it usually will if it's the same brand and not something old and obsolete. One other thing to note, 200A frame 65kaic breakers will usually series rate all the way down to 10k branches. However 400 amp frame breakers usually will not. Of course if you have some sort of spec that states q certain interrupting rating, you have to do what it says even if not needed.
 
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