MCCB kA rating...

[Mike01]

Looking at a SCCAF study in one location the panelbaord branch breakers are rated 10kAIC, the fault current at this location is determined to be slightly less than 10kA however with the calculated x/r greater than the tested x/r when you factor in the multiplying factor [MF] the de-rated kA rating or the increased kA based on the MF [depending on how you look at it] exceeds the rating of the breaker, however the main in the panel is rated at 22kA and the manufacturer series list the main with the branch breaker, so the series rating of the branch breaker is 22kA would this still apply with the higher x/r? For instance if the kA calculates to 12kA based on the higher x/r can the breaker still be series rated to 22kA, looking at the adjusted value, as the x/r is unchanged?

 

[ron]

I couldn't back this up with a standards reference, but when I calculate the required SCCR (including the x/r derating where needed), I consider the series rated value to be adequate if it meets the derated calculated value.

I've never thought about whether the series rating is affected by x/r any different than a fully rated singleton device.