AIC & SCC Relationship

Status
Not open for further replies.
electrofelon said:
. I guess the way I think about it and what seems most logical to me, is that the panel board, which is the bus assembly itself, has a sccr and I don't see why installing one breaker over another should modify that
Click to expand...
Maybe because the definition of panelboard in Article 100 includes both the bus and the automatic overcurrent devices.
 
electrofelon said:
Ok but OCPD's don't have SCCR's, so I don't see what that has to do with it. The SCCR does not change depending on what breaker is added.
Click to expand...
Yes it does.

A piece of equipment's Short Circuit Current Rating ( SCCR) is an all inclusive value based on the SCCRs and AICs of all of the individual components contained within that equipment. This true whether it is a circuit breaker distribution panelboard, a switchboard, a Motor Control Center, or a custom control cabinet.
 
jim dungar said:
Yes it does.

A piece of equipment's Short Circuit Current Rating ( SCCR) is an all inclusive value based on the SCCRs and AICs of all of the individual components contained within that equipment. This true whether it is a circuit breaker distribution panelboard, a switchboard, a Motor Control Center, or a custom control cabinet.
Click to expand...
Agreed except for control panels only components in power circuits have to have an SCCR or AIC rating. Control circuits UL does not care about.
 
Guys, this is a matter of "philosophy" and you will not change my thinking of what is most logical. You are entitled to your view of what is most logical. Perhaps y'all misunderstood, but I am not debating the way it is or that it changes anything in practice.
 
electrofelon said:
Guys, this is a matter of "philosophy" and you will not change my thinking of what is most logical. You are entitled to your view of what is most logical. Perhaps y'all misunderstood, but I am not debating the way it is or that it changes anything in practice.
Click to expand...
It is not just philosophy, it is fact.

According to UL, the overall SCCR of installed equipment is dependent on the SCCR and AIC of what is installed in it.
 
jim dungar said:
It is not just philosophy, it is fact.

According to UL, the overall SCCR of installed equipment is dependent on the SCCR and AIC of what is installed in it.
Click to expand...
I am not disputing that Jim. It just annoys me that the sccr changes depending on what breaker you put in. It doesn't seem logical to me. In my perfect world it would be like the "weakest link" method like we have for ampacity, terminal temperature ratings, etc. Do I have your permission to think that or do I need to go to a re-education camp? 😉
 
electrofelon said:
I am not disputing that Jim. It just annoys me that the sccr changes depending on what breaker you put in. It doesn't seem logical to me. In my perfect world it would be like the "weakest link" method like we have for ampacity, terminal temperature ratings, etc. Do I have your permission to think that or do I need to go to a re-education camp? 😉
Click to expand...
You need to be educated.

If the available short circuit current exceeds the AIC rating of a breaker, it cannot break the short circuit current that might be imposed on it, which is one of its main jobs.

So if you have a CB with a 10kAIC rating and a 20kA SCC occurs, there is some chance the CB will not trip. Thus the panel as a whole would fail as well.
 
electrofelon said:
There is no reason to go higher AIC than needed, except if planning for future increases of the available fault current. I think it is fairly common for specs to say 65k, most likely that is because someone just doesn't want to or doesn't know how to calculate the available fault current, and thinks 65k should cover it (which does in most cases).
Click to expand...
there is an app for that. :)
 
petersonra said:
You need to be educated.

If the available short circuit current exceeds the AIC rating of a breaker, it cannot break the short circuit current that might be imposed on it, which is one of its main jobs.

So if you have a CB with a 10kAIC rating and a 20kA SCC occurs, there is some chance the CB will not trip. Thus the panel as a whole would fail as well.
Click to expand...
Why would the panel fail? It is certainly possible there could be collateral damage if the underdutied breaker failed catastrophically. I understand too that there is time component to a SCCR - my panelboard that says 200k SCCR likely can't take that forever. The shorter the clearing time the higher the sccr. But that would only happen if there is no OCPD ahead of the panelboard, in other words a MLO service panel. My reading of the label in post 20 is that except in the case of an mlo service panel, The sccr remains 200k even if there are lower OCPDs installed.
 
electrofelon said:
Why would the panel fail? It is certainly possible there could be collateral damage if the underdutied breaker failed catastrophically. I understand too that there is time component to a SCCR - my panelboard that says 200k SCCR likely can't take that forever. The shorter the clearing time the higher the sccr. But that would only happen if there is no OCPD ahead of the panelboard, in other words a MLO service panel. My reading of the label in post 20 is that except in the case of an mlo service panel, The sccr remains 200k even if there are lower OCPDs installed.
Click to expand...
The bottom line is the kAIC of the breaker. It doesn't matter if the panel can handle 65kA of fault current if the breaker downstream from it cannot interrupt it.
 
electrofelon said:
I am not disputing that Jim. It just annoys me that the sccr changes depending on what breaker you put in. It doesn't seem logical to me. In my perfect world it would be like the "weakest link" method like we have for ampacity, terminal temperature ratings, etc. Do I have your permission to think that or do I need to go to a re-education camp? 😉
Click to expand...
I think everyone is saying the same thing, but just in a different way.

The SCCR of the component doesn't change based on what breaker is put in. The SCCR of the assembly is what changes.
 
electrofelon said:
My reading of the label in post 20 is that except in the case of an mlo service panel, The sccr remains 200k even if there are lower OCPDs installed.
Click to expand...
Read it again.
That label talks about the rating of the lowest rated device being the SCCR rating of the panel unless a series rating is involved. Yeah I know there are a bunch of commas, separating three different possibilities, but its language is similar to what is used by other manufacturers.
 
Last edited:
Rock86 said:
...and the panelboard SCCR is 200,000A, ...
Click to expand...
Just so that you fully understand, the SCCR of the PANELBOARD with nothing in it (not even lugs) can be as high as 200kA, but the moment you put a breaker in it, the SCCR of the ASSEMBLY becomes whatever the lowest breaker rating (or series rating) is. So the only way to attain an actual 200kA SCCCR on that panel would be to install a Main that is rated 200kAIC, then all feeders rated the same, or if Siemens has SPECIFICALLY done a Series Listing of the feeders and branch breakers in conjunction with that 200kAIC Main.
 
Jraef said:
Just so that you fully understand, the SCCR of the PANELBOARD with nothing in it (not even lugs) can be as high as 200kA, but the moment you put a breaker in it, the SCCR of the ASSEMBLY becomes whatever the lowest breaker rating (or series rating) is. So the only way to attain an actual 200kA SCCCR on that panel would be to install a Main that is rated 200kAIC, then all feeders rated the same, or if Siemens has SPECIFICALLY done a Series Listing of the feeders and branch breakers in conjunction with that 200kAIC Main.
Click to expand...
Yup, I understand that portion of things. Thanks for that.
 
Status
Not open for further replies.
Top