What Is an Overload Heater? As a thermal overload protection element, overload heaters are often found in overload relays that protect motors against overcurrent. A low-resistance metal strip produces heat as the motor pulls current from the current, simulating its thermal properties. In contrast to fuses, they don't burn up and break the current. Unlike fuses and circuit breakers, which provide overcurrent protection for power conductors, overload heaters prevent electric motors from overcurrent.