Mixed KAIC Breakers

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mbrooke

mbrooke

Batteries Included
Location
United States
Occupation
Technician
Does code allow breakers with an AIC less than the busbar to be placed in the panel? I'm not sure what to make of panel MDP.



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Yes as long as the available fault current is less than the lowest rated breaker. The 10K rated breaker would lead one to believe that there is less than 10K available. But then why have far more costly higher rated breakers in the same panel? Makes no sense to me.
 
texie said:
Yes as long as the available fault current is less than the lowest rated breaker. The 10K rated breaker would lead one to believe that there is less than 10K available. But then why have far more costly higher rated breakers in the same panel? Makes no sense to me.
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That makes two of us :)

Question, is a series combination is used, the main OCPD must be in the panel, correct?
 
Who knows how they ended up with what they have. As long as the end product meets all the requirements it just doesn't really matter. Maybe they did a survey of an existing installation and that's what's there.

Interesting that there are two feeders to building a. Unless building a is where the main distribution panel is located that would appear to be a violation of the code.
 
texie said:
Yes as long as the available fault current is less than the lowest rated breaker. The 10K rated breaker would lead one to believe that there is less than 10K available. But then why have far more costly higher rated breakers in the same panel? Makes no sense to me.
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Many designers have default AIC ratings which they use in their specs, like 65kAIC at 480V, as the available fault is often not known until the POCO delivers a transformer. Once the contractor knows that the spec'd and approved equipment is okay they rarely ask for a change order to supply lower rated devices.
 
jim dungar said:
Many designers have default AIC ratings which they use in their specs, like 65kAIC at 480V, as the available fault is often not known until the POCO delivers a transformer. Once the contractor knows that the spec'd and approved equipment is okay they rarely ask for a change order to supply lower rated devices.
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I understand that. But why have mixed values in the same panel?
 
Original project supplied with 65k breakers per boilerplate specs. NEC required label showing available fault current of 9kA. During an expansion the new contractor adds circuits with breakers with standard AIC ratings of 10k and 22k.
 
jim dungar said:
Original project supplied with 65k breakers per boilerplate specs. NEC required label showing available fault current of 9kA. During an expansion the new contractor adds circuits with breakers with standard AIC ratings of 10k and 22k.
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Most likely the case here.
 
Another possibility is that a junior engineer thought you selected interrupting capacity based on downstream requirements rather than source.
 
GeorgeB said:
Another possibility is that a junior engineer thought you selected interrupting capacity based on downstream requirements rather than source.
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Yeah it almost looks like they ran their calcs and are showing values for downstream devices within MDP. On another note, are the 60A's fed from a 2000A possible? Without larger amp electronic trip unit turned down to 60A that is.
 
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