What type of failure will fuses and circuit breakers not protect electric motors against?

Fuses and circuit breakers are designed to protect electrical circuits from excessive current that can cause damage. They effectively address conditions such as short circuits, where there is an unintended low-resistance path that allows an excessive amount of current to flow, and heavy overloads, where the load exceeds the normal operating capacity of the circuit.

However, overheating in electric motors is often caused by prolonged operation at high temperatures, which might not necessarily draw excess current through the circuit. Fuses and circuit breakers typically react to immediate overcurrent conditions, so they might not trip in scenarios where a motor is running under conditions leading to gradual overheating without surpassing their immediate trip thresholds. This gradual accumulation of heat can lead to motor failure, which is termed burnout. Therefore, while fuses and circuit breakers protect against certain electrical faults, they do not provide direct protection against the slow damage to motors that occurs from overheating.