Selecting an Appropriate OCPD

For engineered series combination systems where circuit breakers are installed in series downstream of overcurrent devices with a higher AIC rating, the engineer shall ensure that the _____ device remains passive during the interruption period of the fully rated device.

a) downstream
b) upstream
c) dynamic impedance
d) current limiting

See answer and applicable Code reference

The correct answer is: a) downstream

Overcurrent protection requirements using circuit breakers are outlined in Part VII of Art. 240. As noted in the second paragraph of Sec. 240.86(A), "For calculated applications, the engineer shall ensure that the downstream circuit breaker(s) that are part of the series combination remain passive during the interruption period of the line side fully rated, current limiting device."

 

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