Motors are normally protected from overload by a ______ device.

Motors are normally protected from overload by a ______ device.

• A. Thermal
• B. Magnetic
• C. Electronic
• D. Hydraulic

Answer: (A)

Overload protection in motors is based on responding to the heat that results from excess current. A thermal protection device uses a temperature-sensitive element, like a bimetal strip or a PTC resistor, that heats up as the winding temperature rises. When the temperature hits the set limit, the device trips and disconnects power, preventing insulation damage and overheating. This approach matches the real issue in motor overload—unwanted heat buildup—so it’s the most reliable way to guard the motor over time. Magnetic protection reacts to high current instantly, which is great for short-circuit conditions but isn’t as well suited for gradual overloads that heat the windings. Electronic protection can monitor current and temperature as well, but the standard, textbook protection for overload is thermal. Hydraulic protection isn’t applicable to electrical motor overload.

Overload protection in motors is based on responding to the heat that results from excess current. A thermal protection device uses a temperature-sensitive element, like a bimetal strip or a PTC resistor, that heats up as the winding temperature rises. When the temperature hits the set limit, the device trips and disconnects power, preventing insulation damage and overheating. This approach matches the real issue in motor overload—unwanted heat buildup—so it’s the most reliable way to guard the motor over time.

Magnetic protection reacts to high current instantly, which is great for short-circuit conditions but isn’t as well suited for gradual overloads that heat the windings. Electronic protection can monitor current and temperature as well, but the standard, textbook protection for overload is thermal. Hydraulic protection isn’t applicable to electrical motor overload.