NewTrend · PTC thermistor motor protection relay
Product overview
NewTrend RP8-02 monitors motor-winding temperature through PTC thermistor probes. It detects thermal overload, an open sensor circuit and a shorted probe circuit. The front selector provides memory or automatic-reset operation, and a Test/Reset button and external reset-contact input support fault recovery. Up to six PTC probes can be connected in series. The 18mm DIN-rail relay uses AC/DC 24-240V and provides 2 spdt output rated 10A AC-1.
Technical selection summary
| Model | RP8-02 |
|---|---|
| Function | PTC thermistor motor protection |
| Control supply | AC/DC 24-240V, 50/60Hz or DC |
| Supply terminals | A1-A2 |
| AC power input | 0.7-3VA |
| DC power input | 0.5-1.7W |
| Supply tolerance | -15% to +10% |
| Sensor terminals | T1-T2 |
| PTC sensor connection | Up to 6 PTC probes in series |
| Maximum cold PTC resistance | 1500Ω total |
| Alarm threshold | 3100Ω ±10% |
| Return threshold | 1650Ω ±10% |
| Probe short-circuit detection | 0-10Ω band; below 10Ω is treated as a fault |
| Sensor open-circuit detection | Open sensing circuit is treated as a fault |
| Reset modes | Memory or No Memory, selected on the front |
| Front control | Test/Reset button |
| External reset | Volt-free Y1-T1 contact without parallel load |
| Minimum reset pulse | 200ms |
| Output contacts | 2 SPDT |
| Output terminals | 11-12-14; 21-22-24 |
| Contact rating | 10A, AC-1 |
| Switching voltage | 250VAC / 24VDC |
| Minimum DC breaking power | 500mW |
| Supply indication | Green LED |
| Output indication | Red R LED on when temperature is normal |
| Mechanical life | 10,000,000 operations |
| Electrical life (AC-1) | 100,000 operations |
| Operating temperature | -20 to +55 degrees C |
| Storage temperature | -35 to +75 degrees C |
| Mounting | DIN rail to EN/IEC 60715; 18mm module |
| Protection | IP20 terminals |
| Operating position | Any |
| Overvoltage category / pollution degree | III / 2 |
| Maximum conductor size | 1 x 2.5mm² or 2 x 1.5mm² |
| Terminal tightening torque | 0.4Nm |
| Body dimensions | 90 x 18 x 64mm |
| Overall height in drawing | 95mm including rail-clip projection |
| Weight | 82g |
| Referenced general standard | IEC 60947-1 |
Operation
- Connect up to six PTC probes in series between T1 and T2. Keep the total cold PTC resistance at or below 1500Ω.
- A thermal fault is declared above the 3100Ω threshold. An open sensor circuit is treated as a fault; a probe-circuit resistance below 10Ω is also treated as a fault.
- In No Memory mode, the relay returns to normal when the sensing resistance is below the 1650Ω return threshold and the circuit is healthy.
- In Memory mode, after the sensor circuit returns to normal, reset using the front Test/Reset button or a volt-free contact between Y1 and T1 for at least 200ms.
- The NO output is open during a fault. The red R LED is on when temperature is normal, as shown in the original function description.
Typical applications
- Motor-winding temperature supervision with series-connected PTC probes
- Thermal protection for frequent starting, heavy-duty operation or reduced motor cooling
- Motor contactor-control panels requiring latched fault indication or automatic reset
View or download RP8-01/02 thermistor motor-protection catalogue (PDF)
Product reference images and drawings
Original PTC specifications and model comparison
Original memory/reset timing, wiring, motor application and dimensions
Use the exact-model terminal diagram for the output contact arrangement. The external reset uses a volt-free Y1-T1 contact without a parallel load, as specified in the original reset instructions. Use a suitably rated contactor to switch the motor load. Installation and wiring must be performed by qualified electricians.
