Circuit Protection Calculation
Circuit Protection Calculation
(OP)
I have a 220V circuit board protected by a 75A breaker, I wish to install 2 new breakers, how do I work out if I need to up the 75A breaker?
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Circuit Protection Calculation
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RE: Circuit Protection Calculation
Mike
RE: Circuit Protection Calculation
To determine if the existing 75A Incomer breaker is adequate for the propopsed increase in switchboard load :-
1.) Measure switchboard existing maximum demand current over 15 minute demand interval.
2.) Add to this max demand the max demand of the proposed new load. Continuous rating of Incomer must be greater than max demand.
3.) Check that the proposed max demand does not exceed the continous rating of main busbar in the switchboard.
4.) Calculate max prospective 3 phase short-circuit current at the switchboard. Interrupt rating of the breakers must be greater than the fault current.
Note: The breakers on the outgoing circuits can have interrupt rating less than prospective fault current only if the incomer and outgoing breakers are current limiting and chosen from the manufactuer's certified tables.
5.) Check grading is provided in the event of a fault downstream from the outgoing breakers.