Switchboard/Panelboard Dimensions vs SCCR rating

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Tainted

Tainted

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Suppose I have a switchboard rated at 2500A and a panelboard rated 800A both are 100kAIC. Would having them be 200kAIC change the dimension? Would they have to become bigger? Thanks
 
Tainted said:
Suppose I have a switchboard rated at 2500A and a panelboard rated 800A both are 100kAIC. Would having them be 200kAIC change the dimension? Would they have to become bigger? Thanks
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Remember, AIC is interrupting rating, for OCPD's. Equipment that doesn't interrupt has a SCCR. Are you referring to the SCCR of the panel board/switchboard, or the AIC of the breakers in the equipment?
 
electrofelon said:
Remember, AIC is interrupting rating, for OCPD's. Equipment that doesn't interrupt has a SCCR. Are you referring to the SCCR of the panel board/switchboard, or the AIC of the breakers in the equipment?
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Oops, just realized that what I said was wrong. Yes I mean SCCR, wish I could change the thread title lol
 
I am not positive, but i don't think dimensions would change. I know some equipment is actually rated 200k by default. Siemens panel boards appear to come with a 200k SCCR standard, I just looked at one the other day and noticed it. This was just a "standard" 208Y/120 factory PB with 10kaic branch breakers.
 
electrofelon said:
I am not positive, but i don't think dimensions would change. I know some equipment is actually rated 200k by default. Siemens panel boards appear to come with a 200k SCCR standard, I just looked at one the other day and noticed it. This was just a "standard" 208Y/120 factory PB with 10kaic branch breakers.
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Thanks for your input. Lets add kAIC to the mix: How about 100kAIC and 100kSCCR fully rated panel compared to 200kAIC and 200kSCCR fully rated panel? Would the size change?
 
Tainted said:
Thanks for your input. Lets add kAIC to the mix: How about 100kAIC and 100kSCCR fully rated panel compared to 200kAIC and 200kSCCR fully rated panel? Would the size change?
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I have never had to use or procure an OCPD over 65kaic, and there are probably others with more experience with larger and high AIC/SCCR equipment, but I dont recall ever seeing physical sizes increase with higher AIC. For example, your typical plug on miniature CB is available in 65k versions and it's the same size.

Sometimes, at 240v we use 480 or 600v OCPD's to get a higher AIC rating. For example one could use a Siemens BQD (the typical 277/480 breaker rated 14k) on a 240 system to get a 65k rating.....or a LGB (65K@480) which would give you 100k at 240. But even that doesn't typically change the size.
 
electrofelon said:
I have never had to use or procure an OCPD over 65kaic, and there are probably others with more experience with larger and high AIC/SCCR equipment, but I dont recall ever seeing physical sizes increase with higher AIC. For example, your typical plug on miniature CB is available in 65k versions and it's the same size.

Sometimes, at 240v we use 480 or 600v OCPD's to get a higher AIC rating. For example one could use a Siemens BQD (the typical 277/480 breaker rated 14k) on a 240 system to get a 65k rating.....or a LGB (65K@480) which would give you 100k at 240. But even that doesn't typically change the size.
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At my old firm, I've seen 100kAIC being thrown around all the time. It is the downstream panels after the main distribution board where they specify 65kAIC or below for circuit breakers. I wanted to know this because I already have equipment laid out in my plans at 100kAIC, 100kSCCR fully rated. I haven't determined the short circuit current yet from the utility. I was concerned the design would drastically change if the available SCCR came out to be more than 100k.
 
I have seen the AIC rating of breakers be limited by their physical size. I have never seen the physical bussing, and therefore equipment size, affected by the SCCR rating, except for the ability to hold the larger protective device. Bus ratings are typically obtained simply by increasing the amount of bracing, which decreases the amount of bus flexing. Another area of concern Is the securing of the incoming conductors, which may necisitate a larger lug compartment.
 
electrofelon said:
So, just to be specific (and making up numbers):. Say you needed a 600 amp OCPD with a high AIC. Is it plausible that the AIC would not be available in that 600 amp frame size and you would have to go up to the next frame size to get what you need?
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Yes.
This is not as common as it used to be but it is possible. I remember both molded case and iron frame breakers from the 90s with this problem.
 
This is a good discussion, I like it.

I suppose one tangent that is possibly related to the OP is size of equipment with fuses vs sizes of equipment with breakers. Not sure of that could happen where things change and a change from one to the other would be advantageous.

Also there are series ratings (if used) which may need consideration.
 
I have never seen breakers rated for more than 100kAIC. So to get 200kAIC I think you would be looking at a fused switchboard, which would be larger than a breaker based panel board or switchboard. But I don’t think the fused switchboard dimensions would change between 100k and 200k.

Generally there is no difference in breaker size going from say 35kAIC to 65kAIC, but going from 65 to 100 kAIC usually means an increase in dimensions, but not “frame size”. But that said, there are no universal truths; breaker mfrs have differences.
 
Above about 45 kAIC it becomes tricky to make breakers depending on the type and design. There are some at 65 k, a few at 100k, and apparently fewer still at 200 kAIC. Compared to those all class J fuses for instance are rated 300 kAIC.

Some breakers such as the old “tribreak” breakers have high ratings simply by incorporating a fuse into the breaker. That makes it the ultimate series rated device. This is fairly common in switchgear and medium voltage high interrupting devices.

The tri-break breakers are really long because they have to incorporate a fuse compartment. Similarly most of the fused cast frame breakers are a little deeper.

The big noticeable change is there is a big price jump on everything over about 25-35 kA except fuses. Sure you can buy 100 kA but you pay for it in price and availability. It is a whole lot simpler and safer to use more than one transformer and don’t use auto transformers. For instance at 480 V, a 1000 kVA transformer works out to 1200 A. That is precisely the maximum size of a panel board instead of a switchboard which is much cheaper. 4% Z gives you 30 kA using infinite bus so you don’t pay the 65 kA premium. On the high side you can do distribution in 12.47 kV or 4.16 kV and as long as you stay under about 700-800 A you will notice that the fused disconnects and even breaker prices are much more modest. At those voltages a lot of equipment is rated 10 kA or around 20 kA but the 10-12 kA stuff is very inexpensive and readily available.

These are things that should be in the IEEE Red book but unfortunately it hasn’t been updated in decades.
 
Tainted said:
Suppose I have a switchboard rated at 2500A and a panelboard rated 800A both are 100kAIC. Would having them be 200kAIC change the dimension? Would they have to become bigger? Thanks
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As Jim D mentioned bracing (of probably same bus) might be the major difference in the switchboard or panelboard.

Breakers - you can normally find 65kA and less all generally fit into same frame size case.

Game might change some for 100 and 200 kA. All likely depends on bracing of components again.

Most such gear is designed at and factory assembled per submitted specifications so many don't get into this issues all that much ---until it is discovered what they have don't quite meet what is needed for whatever reason.
 
I mostly use AB, Siemens, and Schneider breakers. There is a premium for 65k breakers but it is not as much as it used to be. it used to be it was a big number but the premium has dropped quite a bit over the years. I've never had anybody spec anything over 65k short circuit current rating so I've never had occasion to use breakers rated more than that, but I have seen some in the catalogs as I am leafing through them, but just never used them.
 
petersonra said:
I mostly use AB, Siemens, and Schneider breakers. There is a premium for 65k breakers but it is not as much as it used to be. it used to be it was a big number but the premium has dropped quite a bit over the years. I've never had anybody spec anything over 65k short circuit current rating so I've never had occasion to use breakers rated more than that, but I have seen some in the catalogs as I am leafing through them, but just never used them.
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I had a recent job where the utility provided number would have been about 75k. Using actual data it was 60k (both infinite primary). I am not sure what the premium would have been to go to 100K equipment but I assumed it would be a jump so I went through the trouble of getting the equipment data and computing it to see if I can get it below 65.
 
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