KAIC rating of panel and breakers

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Fred B

Fred B

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Location
Upstate, NY
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Electrician
Having brain fart, if I've got a panel listed as 22KAIC do I have to provide a breaker rated as 22KAIC or can a 10KAIC rated breaker be put in? What about Visa versa? With such shortages of breakers going on it seems it might be harder to meet one way or other.
 
mopowr steve said:
Should be able to use the lower as long as the available fault current isn’t higher than the breaker your planning to use.
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Wouldn't the panel that is there have presumably been sized to the available fault current? If so wouldn't the 22kaic main say I use a 22kaic branch breakers?
 
You may be thinking of series rated equipment. It is common to find load centers shown as 22/10, having a 22kAIC main breaker and then accepting 10kAIC branch breakers.
 
jim dungar said:
You may be thinking of series rated equipment. It is common to find load centers shown as 22/10, having a 22kAIC main breaker and then accepting 10kAIC branch breakers.
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So if panel is listed as such, either rated branch breaker acceptable but if the panel is not marked in such a way it would require the 22KAIC branch breaker?
 
And if the panel is rated 10KAIC, and only breaker readily available is a 22KAIC, any issues in using the higher rated breaker?
 
Fred B said:
And if the panel is rated 10KAIC, and only breaker readily available is a 22KAIC, any issues in using the higher rated breaker?
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The panel overall SCCR rating is equal to the lowest device, so in your example it would be the buss rating not that of the breakers.
 
jim dungar said:
The panel overall SCCR rating is equal to the lowest device, so in your example it would be the buss rating not that of the breakers.
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Is there anything about utilization equipment that would dictate the need for a particular KAIC for the breaker or panel? Ie HVAC equipment,.
 
Fred B said:
Is there anything about utilization equipment that would dictate the need for a particular KAIC for the breaker or panel? Ie HVAC equipment,.
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I have seen some equipment that specifies a particular fuse (current limiting often a "CC") due to series rating on the utilization equipment
 
The calculation procedure is in the Cooper/Bussmann SPD Selection Handbook.

To calculate short circuit current you start at a point where you know what the maximum is. If you don’t know there is a simple calculation to calculate the maximum possible through a transformer as a starting point. You also have to add contributions from motors but if nothing is over 25 HP you can effectively ignore that. The current drops significantly from line impedance. The Cooper book has a simple calculation for that. You may want to do it once for the service drop and each feeder going to the HVAC.

Going the other way as long as the equipment ratings (SCCR or AIC) exceed the short circuit current, no issues. If they don’t then the solutions are to either reduce fault current or increase AIC or SCCR.

Don’t go too much by what somebody else did. If a motor goes to ground or somebody made a wiring mistake you don’t want to eat the warranty claim for the damage it causes.

You can reduce it two ways. There are ways to do this with fuses…see the Cooper book. Or you can introduce an isolation transformer or line reactors. These can cause additional issues with motor starting too.

The problem is say an MDP is rated 22 kA. So then somebody else comes along and puts in a new breaker either off the truck or purchased. The various grades (10, 22, 35, 65) vary drastically in price. So if they put in the cheapest one (10 kA) and don’t know the difference now your panel is only 10 kA. It’s even common in industrial plants where a purchasing person is buying say “20 A breakers” and sees 4 listings on Graingsr or worse, Amazon.
 
paulengr said:
The problem is say an MDP is rated 22 kA. So then somebody else comes along and puts in a new breaker either off the truck or purchased. The various grades (10, 22, 35, 65) vary drastically in price. So if they put in the cheapest one (10 kA) and don’t know the difference now your panel is only 10 kA. It’s even common in industrial plants where a purchasing person is buying say “20 A breakers” and sees 4 listings on Graingsr or worse, Amazon.
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Which is not a problem as long as your available fault current is under 10 kA. You have not "violated the listing of the panel" or caused any collateral problems.
 
Fred B said:
Having brain fart, if I've got a panel listed as 22KAIC do I have to provide a breaker rated as 22KAIC or can a 10KAIC rated breaker be put in? What about Visa versa? With such shortages of breakers going on it seems it might be harder to meet one way or other.
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This confusion of yours can all be solved if at plan review stage NEC calls for short circuit study with computer program PE stamp sign and seal then engineers tell you what exactly is needed.
 
hhsting said:
This confusion of yours can all be solved if at plan review stage NEC calls for short circuit study with computer program PE stamp sign and seal then engineers tell you what exactly is needed.
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Not in upstate NY.
Did check the equipment and the panel today. Panel is listed 10/22KAIC. The hvac has a nameplate rating listed short circuit current 5kA. Minimum circuit ampacity 36.3. Maximum circuit breaker size 45A.

The current configuration is a 30 pullout disconnect, and a 50A breaker. Something doesn't add up as is. Maybe that is part of why the disconnect melted down.

Right now the 45A breaker is on back order and no time frame for getting one, kind of wondering if the 40A that is available would be adequate.
 
If the pullout is rated 30 amps I'm not surprised it melted down.
The 40 amp breaker will suffice until you get the 45.
The 50 was a violation
 
Fred B said:
And if the panel is rated 10KAIC, and only breaker readily available is a 22KAIC, any issues in using the higher rated breaker?
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No issues.
Fred B said:
Wouldn't the panel that is there have presumably been sized to the available fault current? If so wouldn't the 22kaic main say I use a 22kaic branch breakers?
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not sure about that, but certain brands of panels are just customarily built as 22k and others 10k. Probably why it was pushed in recent years to do available fault current calculations so that we would be more mindful of the equipment we’re installing being able to handle the fault current, as well as arc flash protection.
 
mopowr steve said:
No issues.

not sure about that, but certain brands of panels are just customarily built as 22k and others 10k. Probably why it was pushed in recent years to do available fault current calculations so that we would be more mindful of the equipment we’re installing being able to handle the fault current, as well as arc flash protection.
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One potential difference is the mechanical strength of the current carrying components, including the bus bars.
Another is the retention of the breakers, which will be subject to magnetic forces too.
 
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