Siemens 420 manual PTC temperature sensor, Temperature Classes

Issue 07/04 3 Functions

Temperature Classes

The permissible temperature rise of electrical machinery (motors) is limited due to the thermal strength of the insulating materials.

Different maximum values are permissible depending on the material used. In compliance with regulations for rotating electrical machinery, a differentiation is made between several temperature Classes (refer to the motor rating plate) and these are assigned to the highest permissible continuous temperature. An excerpt from IEC 85 is shown in the "Thermal Classes" table.

Table 3-25 Thermal classes

Excerpt from IEC 85
Thermal Class	Max.perm.temperature
Y	90 °C
A	105 °C
E	120 °C
B	130 °C
F	155 °C
H	180 °C

3.19.2	PTC temperature sensor
	When the motor is operated below the
	rated speed the cooling effect of the
	shaft-mounted fan is reduced. As a
	result, for most motors when continually
	operated at lower frequencies, the
	power has to be reduced. Under these
	particular conditions, the motors are
	only protected against overheating if
	either the parameters of the motor
	temperature model (refer to Section
	3.19.1) were precisely determined or a
	PTC temperature sensor is mounted to
	the motor and connected to one of the
	digital inputs of the MICROMASTER
	420 (refer to Fig. 3-57).
	Parameters P0701, P0702 or P0703 =
	29 (external fault) should be set to
	activate the shutdown (tripping) function
	for a motor overtemperature condition.
	If the resistance of the PTC temperature	Fig. 3-57	PTC characteristic for
	sensor exceeds the shutdown (trip)		1LG / 1LA motors
	threshold (motor overtemperature

condition), then Fault F0085 is output (external fault).

MICROMASTER 420	Operating Instructions
6SE6400-5AA00-0BP0	137