Motor Protection PTC Thermistor
What is a Motor Protection PTC Thermistor?#
A motor protection PTC thermistor is a positive temperature coefficient (PTC) temperature sensor designed specifically for thermal protection of electric motor windings.
Embedded directly into the stator winding, the sensor continuously follows the winding temperature. Once its nominal response temperature is reached, the resistance rises sharply, allowing a dedicated motor protection relay to disconnect the motor before insulation damage occurs.
Motor protection PTC thermistors are standardized by DIN 44081 and DIN 44082, which define the electrical characteristics and switching behavior required for reliable motor protection.
| Standard | Scope |
|---|---|
| DIN 44081 | Requirements for individual motor protection PTC thermistors |
| DIN 44082 | Additional requirements for PTC thermistors connected in series for motor winding protection |
Typical Resistance-Temperature Characteristic#
Tk (nominal response temperature) refers to the temperature at which the PTC thermistor exhibits its characteristic rapid increase in resistance. To comply with DIN 44081 and DIN 44082, the following parameters must be met for all PTC suppliers.
- R25 ≤100 Ω
- R(Tk−5K) ≤550 Ω
- R(Tk+5K) ≥1330 Ω
- R(Tk+15K) ≥4 kΩ
Technical specifications#
| Parameter | Single PTC | Triple PTC | Unit |
|---|---|---|---|
| Max. DC Operating Voltage | 30 | 30 | V |
| Tk (Nominal Response Temperature) | 60–180 | 60–180 | °C |
| Tk Tolerance | ±5 | ±5 | K |
| Tk Reproducibility | ±0.5 | ±0.5 | K |
| Resistance at 25°C (R25) | ≤100 | ≤300 | Ω |
| Resistance at (Tk − 5 K) | ≤550 | ≤1650 | Ω |
| Resistance at (Tk + 5 K) | ≥1330 | ≥3990 | Ω |
| Resistance at (Tk + 15 K) | ≥4 | ≥12 | kΩ |
| Thermal Response Time (Td) | ≤5 | ≤5 | s |
| Dielectric Withstand | AC 2.5 | AC 2.5 | kV |
| Max. Operating Temperature | 200 | 200 | °C |
| Max. Storage Temperature | 160 | 160 | °C |
| Min. Storage Temperature | −25 | −25 | °C |
| Weight | 2 | 3.5 | g |
Standard Dimensions#
Drawing for single core PTC thermistor
Drawing for triple core PTC thermistor
Note:
- Lead wires available in FEP, PTFE, fiberglass
- Standard lead length: 500mm (custom length upon request)
- Standard sensor spacing for multiple core PTC: 200mm (custom spacing upon request)
PTC Identification and Part Numbers#
The color of the PTC connection leads identifies the rated Nominal Response Temperature Tk. They are defined in DIN 44081/082 as shown in the following table. The corresponding part numbers of the SINOMAS PTC are also listed.
- SMP refers to our product category of Motor Protection PTC
- E stands for single core PTC
- D stands for triple core PTC
- The color of the inter-connection wire for multiple core PTC is yellow
| Tk (°C) | Lead Wire Color | Single Core PTC (DIN 44081) | Triple Core PTC (DIN 44082) |
|---|---|---|---|
| 60 | White/Grey | SMP-60-E | SMP-60-D |
| 70 | White/Brown | SMP-70-E | SMP-70-D |
| 80 | White/White | SMP-80-E | SMP-80-D |
| 90 | Green/Green | SMP-90-E | SMP-90-D |
| 100 | Red/Red | SMP-100-E | SMP-100-D |
| 110 | Brown/Brown | SMP-110-E | SMP-110-D |
| 120 | Grey/Grey | SMP-120-E | SMP-120-D |
| 130 | Blue/Blue | SMP-130-E | SMP-130-D |
| 140 | White/Blue | SMP-140-E | SMP-140-D |
| 145 | White/Black | SMP-145-E | SMP-145-D |
| 150 | Black/Black | SMP-150-E | SMP-150-D |
| 155 | Blue/Black | SMP-155-E | SMP-155-D |
| 160 | Blue/Red | SMP-160-E | SMP-160-D |
| 170 | White/Green | SMP-170-E | SMP-170-D |
| 180 | White/Red | SMP-180-E | SMP-180-D |
See also silicone strip heater for anti-condensation protection