AC Motor Overheat Protection Device

If a motor in operating status locks due to overload, the ambient temperature rises rapidly, or the input current increases for some reason, the motor's temperature rises abruptly. If the motor is left in this state, the insulating performance within the motor may deteriorate, reducing its life and, in extreme cases, scorching the winding and causing a fire. In order to protect the motor from such thermal abnormalities, our motors are recognized by UL Standards, CSA Standards, EN Standards and IEC Standards and are equipped with the following overheat protection device.

Thermal Protector

Motors with a frame size of 70, 80, 90 or 104 mm contain a built-in automatic reset type thermal protector.^*
The structure of a thermal protector is shown in the figure below.

• *The KIIS Series doesn't have a built-in overheat protection device (thermal protector), so an electromagnetic switch or the electrothermal function of an inverter must be used.

The thermal protector employs a bimetal system.

Operating Temperature of Thermal Protector

Open:

130±5 °C
(Operating temperature may vary depending on the model.)

Close:

85±20 °C
(Operating temperature may vary depending on the model.)

(The motor winding temperature, where the thermal protector is activated, is slightly higher than the operating temperature listed above.)

Impedance Protected Motors

Motors with a frame size of 60 mm or less are equipped with impedance protection.
Impedance protected motors are designed with higher impedance in the motor windings so that even if the motor locks, the increase in current (input) will be minimized and temperature will not rise above a certain level.

For information on the overheat protection of each product, please refer to the product page.