Which device provides delayed response to overload conditions?

• A. Thermal Overload
• B. Magnetic Contactor
• C. Varistor
• D. Fuse

Answer: (A)

Time-delayed protection for overloads is provided by a thermal overload. It senses the current as heat, using a heater element that heats a bimetal strip. When current stays above the set limit, the heat causes the strip to bend and eventually trip the circuit after a built-in delay. This delay lets brief overloads or startup surges pass without nuisance trips, while sustained overloads are eventually shut off.

This approach is different from a fuse, which is designed to interrupt current quickly with little to no intentional delay. A magnetic contactor is mainly a Switch that can shut off in response to its coil energizing or de-energizing and does not inherently provide time-delayed protection for overloads. A varistor clamps high voltages to protect equipment, but it doesn’t provide a controlled time delay for overload current.

So, the device that best provides a delayed response to overload conditions is the thermal overload.