Current Limiting OCPD's

Grouch

Grouch

Senior Member
Location
New York, NY
I understand that if it is decided to use current limiting fuses / circuit breakers to protect a downstream circuit breaker, that combination has to be series rated, due to the presence of dynamic impedance. If the downstream equipment is an appliance with passive impedance, then there is no need for the series rating, and you can freely use the current limiting OCPD.

Is there any concern with a current limiting OCPD feeding a downstream control panel, or a downstream EV charging cabinet? Control panels and charging cabinets have integral fuses and circuit breakers. Is there any concern with dynamic impedance? Or can one specify a current limiting OCPD without worrying about any series ratings with the integral fuses / breakers in the control panel or charging cabinet.

I'm asking since I have an available short circuit current at the line side terminals of several items that is higher than their SCCR ratings.
 
Grouch1980 said:
If the downstream equipment is an appliance with passive impedance, then there is no need for the series rating, and you can freely use the current limiting OCPD
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Have you ever seen this type of documentation in writing? In literature, I have seen passive devices mentioned as conductors and busbars.
 
jim dungar said:
Have you ever seen this type of documentation in writing? In literature, I have seen passive devices mentioned as conductors and busbars.
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So the answer is no then I presume. I should not be specifying a current limiting OCPD to protect (short circuit wise) a downstream control panel or EV charging cabinet?
 
What's the term again for equipment that does not exhibit dynamic impedance, such as wire or bus bars? Is it referred to as having 'static' or 'passive' impedance?
 
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