How to Select the Right Thermal Relay
2025-08-07
Introduction to Thermal Relays
Thermal relays are essential protective devices that prevent motor damage from overload conditions by monitoring current flow and responding to abnormal temperature rises. At SONTUOEC, we manufacture precision thermal relays designed for industrial motor protection applications. This comprehensive guide provides expert insights into selecting, installing, and maintaining thermal relays for optimal equipment protection.
Key Selection Criteria for Thermal Relays
1. Current Rating Parameters
| Parameter | Importance | SONTUOEC Standard |
|---|---|---|
| Setting Current Range | Must match motor FLA | 0.1-80A adjustable |
| Trip Class | Response speed | Class 10A, 20, 30 |
| Ambient Compensation | For varying temperatures | ±5% accuracy |
2. Technical Specifications
| Model | Current Range | Trip Class | Contact Rating | Mounting Type |
|---|---|---|---|---|
| ST-TR10 | 0.1-10A | 10A | 5A/440VAC | DIN Rail |
| ST-TR25 | 5-25A | 20 | 10A/600VAC | Screw |
| ST-TR80 | 20-80A | 30 | 15A/690VAC | Panel |
3. Environmental Considerations
✔ Operating temperature: -20°C to +60°C
✔ Humidity resistance: 95% RH non-condensing
✔ Vibration resistance: 5-100Hz, 1.5mm amplitude
SONTUOEC Thermal Relay Product Line
Performance Comparison
| Feature | ST-TR10 | ST-TR25 | ST-TR80 |
|---|---|---|---|
| Response Time | <5min | <10min | <20min |
| Reset Method | Manual | Auto/Manual | Auto/Manual |
| Phase Loss Protection | Yes | Yes | Yes |
| Certifications | CE, UL | CE, UL, RoHS | CE, UL, CCC |
Advanced Features
✔ Bi-metallic strip technology for precise tripping
✔ Phase failure protection (critical for 3-phase motors)
✔ Test button for periodic verification
✔ Dual indicator lights (power/trip status)
Installation and Configuration Guide
Step-by-Step Setup
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Calculate motor full load current (FLA)
-
Select relay with matching current range
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Set current dial to 105-125% of FLA
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Connect properly sized conductors
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Verify operation with test button
Maintenance Best Practices
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Monthly: Visual inspection for damage
-
Quarterly: Test trip functionality
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Annually: Calibration check
FAQ: Thermal Relay Selection
Q: How do I choose between different trip classes?
A: Select based on motor characteristics:
| Trip Class | Response Time | Best For |
|---|---|---|
| Class 10A | Fast (5-10 sec) | Small motors, pumps |
| Class 20 | Medium (10-20 sec) | General purpose motors |
| Class 30 | Slow (20-40 sec) | High inertia loads |
SONTUOEC recommends:
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Class 10A for precision equipment
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Class 20 for most industrial applications
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Class 30 for crushers, compressors
Why Choose SONTUOEC Thermal Relays?
✔ 0.5% current setting accuracy
✔ 50,000+ mechanical operations
✔ Universal compatibility with major contactors
✔ 5-year warranty on core components
✔ Custom calibration services available
Get Expert Motor Protection Solutions
For technical specifications or application support:
📞 Tel: +86-13868610160
📧 Email: [email protected]
With decades of experience in electrical protection, I personally guarantee SONTUOEC thermal relays provide reliable motor protection in the most demanding environments. Contact us today for your project requirements!