What determines the AIC rating of a MLO panel

[qcroanoke]

Is it determined by the breaker upstream or the main lugs and buss of the panel?
We have a customer we are telling it is 22,000 AIC. But I'm thinking it's only as good as the breaker feeding the panel.
Thanks!

 

[charlie b]

The panel's rating is determined by its manufacturer. It is the highest amount of current to which the manufacturer subjected the panel in a test, and it is the amount that the manufacturer affirms that the panel can withstand.

It is a different topic if you wish to determine if the panel is suited for its intended application. First, you need to know the amount of fault current that the power system will inflict on the panel; that value must be lower than the panel's rating. Secondly, you need to have any components upstream of that panel, including the panel's feeder breaker, rated for the amount of current that will be seen at their respective locations.

If, for example, the panel is rated for 22,000 AIC, and if the amount of fault current seen at the breaker's location is only 8,000 AIC, then you could use a breaker rated for 10,000 AIC. The breaker's rating need not match that of the panel it serves. Rather, the breaker's rating must be at least as high as the fault current available at its location.

 

[don_resqcapt19]

I thought that the term AIC only applied to a device that is intended to open fault current. There should be a withstand rating for the panel itself.

 

[winnie]

A _panel_ does not have an AIC rating; because it is not intended to interrupt current.

The panel should have a maximum short circuit current rating, which should be greater than the available fault current at its location.

-Jon

 

[qcroanoke]

A _panel_ does not have an AIC rating; because it is not intended to interrupt current.

The panel should have a maximum short circuit current rating, which should be greater than the available fault current at its location.

-Jon

Sorry, I was quoting what our bid letter said.
Guess I'd better have a talk with marketing about the verbage they use
when quoting a job.

 

[jim dungar]

This is an example of how we have let exact terminology in our industry get muddied.

While a panelboard does not have an AIC rating, the breakers in it will have one.

If you are bidding or specifying a MLO panel its resulting SCCR will depend upon which breakers are install in it.

 

[winnie]

Jim,

You are correct, and I apologize to gcroanoke. I was being uselessly pedantic in my comment.

AIC and SCCR are _different_ fault current ratings. IMHO it is important to know the difference, and to distinguish between the two. Perhaps it would have been usefully pedantic for me to describe the two. But sometimes a cola is a cola and it really doesn't matter if it is Coke or Pepsi

AIC is the fault current that a dynamic device (such as a breaker) can interrupt.

SCCR is the fault current that static device (such as a bus bar) can survive without damage.

The MLO panel itself will have a short circuit withstand rating. But as Jim says, if the panel is actually being sold with breakers in it, then the interrupting rating of the breakers is for all practical purposes the 'AIC of the panel'...unless someone is really dumb and puts breakers of high AIC in a panel that itself has low SCCR

-Jon

 

[jim dungar]

The MLO panel itself will have a short circuit withstand rating. But as Jim says, if the panel is actually being sold with breakers in it, then the interrupting rating of the breakers is for all practical purposes the 'AIC of the panel'...unless someone is really dumb and puts breakers of high AIC in a panel that itself has low SCCR

-Jon

Jon, I wasn't directing my comments specifically a you, but you knew that I hope.

The biggest problem I see is people ignoring the SCCR of the panel entirely when adding breakers. I often see installed panels with SCCR stickers on them that have had breakers, with a lower AIC rating, field added with the defence "the breaker doesn't matter, its the panel the inspector cares about".

 

[qcroanoke]

Jim,

You are correct, and I apologize to gcroanoke. I was being uselessly pedantic in my comment.

AIC and SCCR are _different_ fault current ratings. IMHO it is important to know the difference, and to distinguish between the two. Perhaps it would have been usefully pedantic for me to describe the two. But sometimes a cola is a cola and it really doesn't matter if it is Coke or Pepsi

AIC is the fault current that a dynamic device (such as a breaker) can interrupt.

SCCR is the fault current that static device (such as a bus bar) can survive without damage.

The MLO panel itself will have a short circuit withstand rating. But as Jim says, if the panel is actually being sold with breakers in it, then the interrupting rating of the breakers is for all practical purposes the 'AIC of the panel'...unless someone is really dumb and puts breakers of high AIC in a panel that itself has low SCCR

-Jon

pedantic? I had to look that one up! LOL!! No,Winnie I don't think so.
No apology nesessary.
The NEC is written and interpeted by the words used and you'd better
understand the verbage.

I now have a better understanding of SCCR and AIC and I thank you ,Jim,
Charlie and Rescue capt. Don for that.
This thread will help me point out that just because the buss and main lugs
are rated 22,000 if you don't install equally rated breakers you do not have
a panel rated 22,000!

 

[benaround]

I'm going to put my 2 cents worth in here. Every elecrtical distribution

system needs a ' Fault Calc.' done ( prefered method by EE ) , this will let

you know the 'Available Fault Current' at each distribution point along the

system, with the highest being closest to the Utility transformer and the

lowest being the last one downstream.

The SCCR of the equipment must be higher than the Available Fault Current

in that section of the system and the ( OPD) circuit breakers ' Amps Interrupting Capacity'

must be higher than the AFC for that same section, the AIC can be as high

as you want to make it, as long as it is higher than the AFC.