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."
About the Author
Mike Holt
Mike Holt is the owner of Mike Holt Enterprises (www.MikeHolt.com), one of the largest electrical publishers in the United States. He earned a master's degree in the Business Administration Program (MBA) from the University of Miami. He earned his reputation as a National Electrical Code (NEC) expert by working his way up through the electrical trade. Formally a construction editor for two different trade publications, Mike started his career as an apprentice electrician and eventually became a master electrician, an electrical inspector, a contractor, and an educator. Mike has taught more than 1,000 classes on 30 different electrical-related subjects — ranging from alarm installations to exam preparation and voltage drop calculations. He continues to produce seminars, videos, books, and online training for the trade as well as contribute monthly Code content to EC&M magazine.