Overcurrent Device Selection & Series Ratings
4:32
Picking a breaker isn't just matching an amp number — the fault current it can handle matters just as much, and series ratings are one of the most misunderstood topics on the exam.
In this lesson: 240.1's core purpose, standard OCPD ratings, the 240.4(B) next-size-up rule with a worked example, the 240.4(D) small conductor hard caps (14/12/10 AWG), interrupting rating (110.9) vs short-circuit current rating (110.10), what a series rating actually is (240.86), the required field marking, how motor contribution can invalidate a series rating, series vs fully rated systems, and how series ratings differ from selective coordination.
