The heater element of a bimetallic overload relay is sized to half of the full-load current.

• A. To full-load current
• B. True
• C. False
• D. To double the full-load current

Answer: (C)

In a bimetallic overload relay, the heater element is the heat source that tells the mechanism when to trip. It’s designed to generate enough heat at roughly the motor’s full‑load current (often with a small margin above it) so that, if current climbs above this level due to overload, the accumulated heat causes the bimetal strip to bend and the relay to trip after an appropriate delay. If the heater were sized to conduct only half of the full‑load current, it wouldn’t produce enough heat under normal operating currents, and the relay would either fail to trip or take much longer to trip when overload occurs. That’s why this statement is false.