PTC Thermistors

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Temperature Sensors

NTC & PTC Thermistors

PTC thermistors act as thermal protectors for electrical motors. They are available with or without an insulated sleeve and have flexible connecting leads. PTC thermistors have a non-linear resistance/temperature response. At a specified temperature the resistance changes rapidly to a very high value.

Rapid response protection for electrical machines

Compact size for easy assembly into windings

Silvered copper leads

PTC Thermistors


Motor Protection and Electronics.

Dimensions (mm)

Single Thermistor
with shrunk-sleeve & epoxy seal

Type Response Temp.
Color Code
YGM1 C508 80±5 white-white
YGM1 C509 90±5 green-green
YGM1 C510 100±5 red-red
YGM1 C511 110±5 brown-brown
YGM1 C512 120±5 grey-grey
YGM1 C513 130±5 blue-blue
YGM1 C514 140±5 white-blue
YGM1 C545 145±5 white-black
YGM1 C515 150±5 black-black
YGM1 C655 155±5 blue-black
YGM1 C516 160±5 blue-red
YGM1 C517 170±5 white-green
YGM1 C518 180±5 red-white

Mount-on Sensor
in isolated brass/aluminium housing

Type Response Temp.
Color Code
CEF1 C508 80±5 white-white
CEF1 C509 90±5 green-green
CEF1 C510 100±5 red-red
CEF1 C511 110±5 brown-brown
CEF1 C512 120±5 grey-grey
CEF1 C513 130±5 blue-blue
CEF1 C514 140±5 white-blue
CEF1 C545 145±5 white-black
CEF1 C515 150±5 black-black
CEF1 C655 155±5 blue-black
CEF1 C516 160±5 blue-red
CEF1 C517 170±5 white-green
CEF1 C518 180±5 red-white

When ordering please specify thread size, otherwise the stock M4 size will be supplied.


Triple Thermistor
with shrunk-sleeve & epoxy seal

Type Response Temp.
Color Code
YGM3 C508 80±5 white-yellow-yellow-white
YGM3 C509 90±5 green-yellow-yellow-green
YGM3 C510 100±5 red-yellow-yellow-red
YGM3 C511 110±5 brown-yellow-yellow-brown
YGM3 C512 120±5 grey-yellow-yellow-grey
YGM3 C513 130±5 blue-yellow-yellow-blue
YGM3 C514 140±5 white-yellow-yellow-blue
YGM3 C545 145±5 white-yellow-yellow-black
YGM3 C515 150±5 black-yellow-yellow-black
YGM3 C655 155±5 blue-yellow-yellow-black
YGM3 C516 160±5 blue-yellow-yellow-red
YGM3 C517 170±5 white-yellow-yellow-green
YGM3 C518 180±5 red-yellow-yellow-white


PTC thermistors exhibit very high sensitivity over a narrow temperature band. For temperature measuremen
in this range, NTC thermistors are easier to measure and more accurate.

PTC thermistors are especially suited as temperature sensors for monitoring the windings of electric machines, and also for use in simple fail-safe circuitry. When a given temperature (nominal response temperature qNAT) is exceeded, the circuit can be switched off through a relay or amplifier, since the PTC-sensor will have an extremely high ohmic value in the region of its response temperature. This will have the same effect as a break in the circuit or a failure of the thermistor.


Nominal response temperature: 80° C to 180° C in steps of 10°, plus 145° and 155°
Max. allowable operating temp. T max. 200° C
Max. allowable operating voltage at +25° C Umax 25V (per bead)
Max. allowable power dissipation at +25° C 690 mW
Insulation strength (between leads and outer insulation) also for threaded sensor 2.5 kV
Conductors – silvered copper wire
with teflon insulation
Insulation stripping approx 10 mm
Conductor cross-section 0.25 mm 2 for single, double and triple PTC’s


Single PTC 500 mm 6 10 mm
Triple PTC 500 – 180 – 180 – 500 mm 6 10 mm


PTC’s are also available in many special housings (can be manufactured to customers specifications)


For PTC temperature sensors in electrical windings:
– the thermistors can only be inserted in the windings before impregnation
– it is advisable to embed one in each phase, if possible in the centre of the coil generating most heat, and generally on the outflow side of any air movement
– air inflow onto the temperature sensor will interfere with heat transfer
– if using varnish/lacquer which is not chemically neutral, suitability tests must be undertaken by the customer
– WARNING! It is very important that the sensor must be installed parallel with the copper of the winding, so that the teflon leads can assume the form of the rest of the winding and thereby retain the highvoltage resistance rating.
– PTC’s are classified according to their nominal response temperature ϑNAT but all have similar resistance characteristics to simplify the choice of switching device; the relationship of resistance to temperature of all these PTC’s is as follows:


Single PTC
Temp. ° C Resistance Ω Measuring Voltage V
-20 to ϑNAT -20 250 max./100max. 2.5
ϑNAT -5 550 max. 2.5
ϑNAT 1.000 2.5
ϑNAT +5 1.330 min. 2.5
ϑNAT +15 4.000 min. 7.5

Triple PTC

Temp. ° C Resistance Ω Measuring Voltage V
-20 to ϑNAT -20 750 max./300max. 7.5
ϑNAT – 5 1.650 max. 7.5
ϑNAT+5 4.000 max. 7.5
ϑNAT +15 4.000 min. * 7.5

* One PTC might reach ϑNAT + 15 °C, while the second or even both of the others could still remain at room temperature.

The PTC’s resistance values for motor protection are specified in DIN 44081/44082. Resistance values below ϑNAT –20 are not specified, and resistance when cold is no indication of the PTC’s condition. It is ideally between 40 – 200 ohms but can be anywhere between 35 – 250 ohms.

The greatest resistance change occurs between +/-5 °C either side of ϑNAT, being at least 15%/K.


Random testing is carried out according to DGQ P90/P10 (DIN 40080). AQL values can be fixed by arrangement.


Quantity Type Temp. Code No. Resistance max.
1.000 YGM1 C 510 250 ohms