If a panelboard is spec'ed with a certain ampere interrupting capacity, do the circuit breakers come labeled with this AIC as well? For instance does a 22 kA AIC panelboard come with 22 kA AIC circuit breakers? I was thinking this would be required if this was the available short circuit current.
Panelboard AIC and C.B. AIC
- Thread starter cppoly
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AIC is a rating for protective devices. The AIC of a device must equal or exceed the fault current available on its line side terminals. The is found in NEC 110.9
SCCR, shart circuit current rating, is the term for non-protective equipment, like panels. The SCCR must be greater than the calculated fault current. NEC 110.10 cover this. You may also see the older terms term Bus Bracing or Withstand Rating
There is nothing that says a panel's rating must be equal to that of a protective device. In fact it is quite common to see bus braced for 100kA and then contain a phrase like "SCCR is equal to the AIC of the lowest installed breaker.
If you specify a 22kA rating for the panel, the UL Listing procedures would expect you to get 22kAIC breakers at the minimum. However it is possible for an improper breaker to be 'field added'.
Keep in mind the manufacturer might be able to "series rate" a panel by using listed combination of breakers.
You could have branch breakers with a lower rating than the Main, but it does not necessarily apply to all breakers.
For instance, a 2 pole 15 might "series rate" where a 3 pole 60 would not.
You could have branch breakers with a lower rating than the Main, but it does not necessarily apply to all breakers.
For instance, a 2 pole 15 might "series rate" where a 3 pole 60 would not.
Jim may correct me as he is top notch on this, however, my answer is "not necessarily."
A 'fully rated' system has all components rated at or above your AI, but, as mentioned in the earlier post, a "series rated" system can have components with a lesser rating that 'series rate' with an upstream over-current device.
It is not unusual in this area to find 22k rated series load centers with a 22k main and 10k branches..
A 'fully rated' system has all components rated at or above your AI, but, as mentioned in the earlier post, a "series rated" system can have components with a lesser rating that 'series rate' with an upstream over-current device.
It is not unusual in this area to find 22k rated series load centers with a 22k main and 10k branches..
If it is specified "fully rated" then that's ALL components. FWIW, in my experience fully rated systems are rare birds.
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- PE (Retired) - Power Systems
Typically we find series ratings only to the final branch circuit panelboard. Primarily, this is because it is extremely rare to be able to rate more than two devices in series (the exception being multi-meter equipment). This means that if there are appreciable size feeders (i.e. >250A) they are often full rated.
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Once again, your valued input has energized some old brain cells
Thinking back, I agree that on larger install (over 2000A), the MDP, MSB, were normally fully rated. My inspection area of late sees few of these larger services and I had forgotten.. Thanks.
- Location
- Wisconsin
- Occupation
- PE (Retired) - Power Systems
Once again, your valued input has energized some old brain cells
Thinking back, I agree that on larger install (over 2000A), the MDP, MSB, were normally fully rated. My inspection area of late sees few of these larger services and I had forgotten.. Thanks.
I do see series ratings on services this size, when there are no intermediate 'feeder panels', but I would not call it a common practice.
Another problem with series ratings, is they cannot be used when there is an appreciable amount of motor loads 'between' the two series rated devices. Motor loading need to be limited to 1% of a device's full rating, so a 22kAIC breaker would be limited to 220A of motor load on the load side of the upstream device. This pretty much limits series ratings to <400A panels in non-industrial settings.
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