When is a shunt trip operated to power down an elevator?

Elevators must beshut downwhen there iswater dischargein the hoistway to prevent electrical hazards and damage. This shutdown is done using ashunt trip breaker.

NFPA 72 (2022), Section 21.4.2:

“Where sprinklers are located in the elevator machine room, control space, or hoistway, means shall be provided to automatically disconnect the main power supply to the elevator prior to the application of water.”

This is triggeredby a waterflow switch or heat detector, but the standard design uses thesprinkler head activationas the point of shutdown via heat detector.

Important: While the heat detector usually triggers the shunt trip, thesprinkler head activationis the condition being detected.

Correct answer: D. When a sprinkler head is activated

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