Quick Hits

Episode 18 — Circuit Breaker Operation, Marking, and Voltage Applications

Covers: 240.80, 240.81, 240.82, 240.83, 240.85

Hook: Breakers have their own dedicated part of the article — trip-free design, tamper resistance, marking, and that confusing slash-rated voltage thing.

Slide 2: Breakers must be trip-free (can't be manually held closed during a trip condition) and manually operable, even if their normal operation is electric or pneumatic. They must clearly show open/closed, and if the handle moves vertically, "up" has to mean "on." Breakers must resist tampering with their trip calibration without dismantling or breaking a seal.

Slide 3: Ampere rating markings must be durable and visible (even if that means removing a trim/cover); breakers rated 100A or less need that rating molded/stamped/etched right into the handle or escutcheon. Interrupting ratings other than 5000A must be marked. Breakers used as switches for fluorescent or HID lighting circuits need SWD or HID listing/marking respectively. Straight-voltage-rated breakers (like "480V") apply where no two conductors exceed that rating; slash-rated breakers (like "120/240V") apply only on solidly grounded circuits where neither the to-ground nor the phase-to-phase voltage exceeds the respective rating.

Quiz: What does a "slash" voltage rating like 120/240V on a breaker actually mean?
Answer: The lower number is the max voltage to ground, the higher number is the max voltage between any two conductors — for use only on solidly grounded systems.

CTA: Follow — series ratings and breaker arc energy reduction are next.

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