AIC ratings, replacing breakers

[sparky486]

The OEM for a project of mine has provided 14k aic breakers to replace 35k going into a sub panel. Sub panel main is 50k, all branch circuit breakers are 35k. No calculated aic on the prints past the 2500a facility main (30,348a). I have always been under the impression that aic is aic is aic, calculated by using wire size, load, and length from utility provided rating at the 1st xfmr. They are trying to tell me that they "derated" the panel by simply providing the 14k breakers. Everything in my head says "no way".... suggestions and/or comments?

 

[jumper]

“They” are nuts.

 

[Ingenieur]

no
make them do a sc study

I guess technically they did derate the panel
from 35k to 14k for those branches
but that does not change the avail fault i for those ckts

 

[Jraef]

It's POSSIBLE that the lower rated breakers can be used in a "Series Rated" system with the main breaker in that panel, and the Series Rating of the entire panel is higher than the individual branch breakers. But that's something that only the MANUFACTURER can certify and generally, it's incumbent on someone making that substitution to also provide the proper documentation showing it, because the AHJ will want to see it.

 

[charlie b]

I have always been under the impression that aic is aic is aic, calculated by using wire size, load, and length from utility provided rating at the 1st xfmr.

Please allow me to split a hair: that is not "AIC." Rather, it is SCCA (Short Circuit Current Available). A breaker's AIC is essentially the amount of current the breaker can interrupt without being destroyed in the attempt. We are required to select a breaker that has an AIC rating that is at least as high as the SCCA that the power system is capable of imposing on its location during a fault. Changing a breaker rated at 35KA with one rated 14KA does not change the amount of fault current that could be seen at that location. Derek is right: "They are nuts."

 

[Jraef]

Please allow me to split a hair: that is not "AIC." Rather, it is SCCA (Short Circuit Current Available). A breaker's AIC is essentially the amount of current the breaker can interrupt without being destroyed in the attempt. We are required to select a breaker that has an AIC rating that is at least as high as the SCCA that the power system is capable of imposing on its location during a fault. Changing a breaker rated at 35KA with one rated 14KA does not change the amount of fault current that could be seen at that location. Derek is right: "They are nuts."

Yes but...

240.86 Series Ratings.
Where a circuit breaker is used on
a circuit having an available fault current higher than the
marked interrupting rating by being connected on the load
side of an acceptable overcurrent protective device having a
higher rating, the circuit breaker shall meet the requirements
specified in (A) or (B), and (C).

then;

(B) Tested Combinations. The combination of line-side
overcurrent device and load-side circuit breaker(s) is tested
and marked on the end use equipment, such as switchboards
and panelboards.
Informational Note to (A) and (B): See 110.22 for marking of
series combination systems.

So it is POSSIBLE that the equipment in question meets (B), but again, if someone is using that justification, they should be providing the proof of it, or the panel should have that information on it (and the new breakers are SPECIFICALLY listed in that documentation)

 

[jumper]

So it is POSSIBLE that the equipment in question meets (B), but again, if someone is using that justification, they should be providing the proof of it, or the panel should have that information on it (and the new breakers are SPECIFICALLY listed in that documentation)

But it more fun to just say they are nuts....:angel:

 

[Jraef]

But it more fun to just say they are nuts....:angel:

Well OK, that's true. :slaphead:

 

[kwired]

The OEM for a project of mine has provided 14k aic breakers to replace 35k going into a sub panel. Sub panel main is 50k, all branch circuit breakers are 35k. No calculated aic on the prints past the 2500a facility main (30,348a). I have always been under the impression that aic is aic is aic, calculated by using wire size, load, and length from utility provided rating at the 1st xfmr. They are trying to tell me that they "derated" the panel by simply providing the 14k breakers. Everything in my head says "no way".... suggestions and/or comments?

There is ~30kA available at the facility main, but impedance of conductors beteween facility main and the panel in question will reduce what is available at that panel. Just 25 -30 feet of conductor can make a significant difference sometimes. On top of that there it is possible the breakers in question are series rated for use with whatever is ahead of them.

Simple applications of QO loadcenters - main breakers are normally rated 22kA - standard 10kA breakers are series rated to be used in the loadcenter even if full 22k is available. If you are more then 25-30 feet from the source in 200 amp or less applications, conductors usually are limiting enough you don't have a problem with available fault current and AIC ratings.

 

[petersonra]

The OEM for a project of mine has provided 14k aic breakers to replace 35k going into a sub panel. Sub panel main is 50k, all branch circuit breakers are 35k. No calculated aic on the prints past the 2500a facility main (30,348a). I have always been under the impression that aic is aic is aic, calculated by using wire size, load, and length from utility provided rating at the 1st xfmr. They are trying to tell me that they "derated" the panel by simply providing the 14k breakers. Everything in my head says "no way".... suggestions and/or comments?

I don't know what they mean when "they" say they "derated" something. It might well be that whatever they did was perfectly acceptable but the guy you talked with did not understand what actually happened and made up this terminology. That happens a lot when people just do not understand what they are talking about.

 

[sparky486]

good info so far folks, thanks.. I like getting to the nuts and bolts of this sort of thing since it isn't generally something that presents itself in the field (at least on our stuff). heck, my journeyman said "90% of those numbers on there are jibberish to me", so it is a good learning opportunity for him as well. (and also let me know I miss some details when trying to educate my men :slaphead: ) keep it coming, I'm holding the OEM to the fire on this one.

 

[kwired]

I don't know what they mean when "they" say they "derated" something. It might well be that whatever they did was perfectly acceptable but the guy you talked with did not understand what actually happened and made up this terminology. That happens a lot when people just do not understand what they are talking about.

They likely did figure the available current was lower at the point in question, "derating" wasn't really the correct terminology to use here though.

 

[Jraef]

I don't know what they mean when "they" say they "derated" something. It might well be that whatever they did was perfectly acceptable but the guy you talked with did not understand what actually happened and made up this terminology. That happens a lot when people just do not understand what they are talking about.

They likely did figure the available current was lower at the point in question, "derating" wasn't really the correct terminology to use here though.

Yeah, I guess a clarification on the term "derated" is in order here. THEY (as an OEM) would not be the ones to make that determination in my opinion, but it is possible that the person making that statement didn't really understand, and what they WERE doing is using a Series Listing of the equipment they provided.

 

[sparky486]

agreed.. the term "derated" tried to get me off center also.. I've written that statement off as poor terminology.. I have had no reply from the OEM other than that, but hopefully they will step up, provide some documentation, or be willing to replace the breakers in question. In the meantime, I'm getting my head wrapped tighter around series rated breakers, 240.86, and how it all can/does/should apply to this situation. If/when they respond, i'll be able to carry on a more intelligent conversation with them. great responses, thanks again