Overheat Protection and Thermal Class for Motors and Fans

1. Motors and Fans with Overheat Protection

1-1. Products with a Built-in Thermal Protector

"THERMALLY PROTECTED" or "TP" is written on the nameplates for products with built-in thermal protectors. The structure of a thermal protector is shown Figure 1.
AC motors and AC fans with a frame size of 70 mm or more have a built-in automatic reset type thermal protector. (This may not apply to all series.)

The thermal protector employs a bimetal system.

• ◇ Thermal Protector Operating Temperature

open:

AC Motor: 130 ± 5 °C
AC Fan: 120 ± 5 °C
(Operating temperature may vary depending on the model.)

close:

AC Motor: 85 ± 20 °C
AC Fan: 76 ± 20 °C
(Operating temperature may vary depending on the model.)

1-2. Impedance-Protected Products

This is applicable to AC motors and AC fans with a frame size of 60 mm or less. (This may not apply to all series.)
"IMPEDANCE PROTECTED" or "ZP" is written on the nameplates for impedance-protected products.
These 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 the temperature rise will not exceed a certain level.

1-3. DC Fans

DC fans are equipped with a burnout prevention circuit that cuts the power to the windings or limits the current when the rotor is locked.

2. Motors without Overheat Protection

2-1. AC Motors

Some AC motors do not have an overheat protective function. They are designed so that, when combined with an inverter, overheat protection is provided by the electrothermal function of the inverter, and when combined with an electromagnetic switch, this protection is provided by the built-in thermal relay of the electromagnetic switch.

2-2. Brushless Motors and Servo Motors

Brushless motors and servo motors are equipped with overload protection features in the combination of motors and drivers, and temperature rises are controlled by shutting down the input power supply from the driver to the motor when an abnormality occurs.

2-3. Stepper Motors

5-phase stepper motors are designed to ensure the temperature will not rise above a certain level when stopping 5-phase excitation at the rated current, and 2-phase stepper motors are designed to ensure temperature rise will not exceed a certain level when stopping 2-phase excitation at the rated voltage.

3. Thermal Class

The thermal class of an electrical insulation system represents the maximum continuous operating temperature recommended for that system, and this is regulated by IEC 60085 (JIS C 4003: Electrical insulation - Thermal evaluation and designation). Based on IEC 60085, the thermal class of rotating electrical machinery, such as motors and fans, is regulated as follows by IEC 60034-18-21 (Rotating electrical machines - Part 18-21: Functional evaluation of insulation systems - Test procedures for wire-wound windings - Thermal evaluation and classification).
The windings must be used in such a way that they do not exceed this temperature.