Fault Current Calc. Question

[KWH]

The local AHJ requires a data log form which I understand from xfmr to main gear but they also need from main gear to interior panels and ask for let thru current from MDP breakers to interior panels. I'm not sure what that means. I can figure from MDP to these panels but the let thru I need help on.

Thanks

 

[charlie b]

The only thing that makes sense to me is that the AHJ wants you to demonstrate that the short circuit current rating (SCCR) of the interior panels is equal to, or greater than, the short circuit current available (SCCA) at their location. That is the essence of a fault current calculation. The SCCA at any panel will be the same as the current that leaves the MDP breaker that feeds that panel. Perhaps that is what they are calling the "let through current."

 

[KWH]

The only thing that makes sense to me is that the AHJ wants you to demonstrate that the short circuit current rating (SCCR) of the interior panels is equal to, or greater than, the short circuit current available (SCCA) at their location. That is the essence of a fault current calculation. The SCCA at any panel will be the same as the current that leaves the MDP breaker that feeds that panel. Perhaps that is what they are calling the "let through current."

That makes sense. I wasn't sure if the value at the interior panel branch circuit breaker is lower than the fault how series rating came into play meaning the MDP breaker@ 65k will protect the 10k rated branch breaker

 

[Smart $]

That makes sense. I wasn't sure if the value at the interior panel branch circuit breaker is lower than the fault how series rating came into play meaning the MDP breaker@ 65k will protect the 10k rated branch breaker

Some background info...

https://iaeimagazine.org/magazine/2017/04/18/current-limitation/
http://static.schneider-electric.us/docs/Circuit Protection/0600DB0301.pdf, page 7
http://www.cooperindustries.com/con...s/training/bus-ele-tr-current-limitation.pptx
http://ep-us.mersen.com/fileadmin/c...tion-Information-Let-Thru-Current-and-I2t.pdf