Overload relays safeguard motors and circuits by preventing damage from excessive current. These critical components detect abnormal electrical loads and interrupt power within milliseconds, protecting equipment from overheating and fire risks. This guide examines their types, operating principles, and industrial applications.
Three Primary Overload Relay Types
| Type | Operating Principle | Optimal Use Cases |
|---|---|---|
| Thermal Overload | Bimetallic strip deformation | Cost-sensitive motor protection |
| Magnetic Overload | Electromagnetic trip mechanism | High-speed fault response |
| Electronic Overload | Microprocessor current monitoring | Precision industrial automation |
CNC’s EOR-Series electronic relays feature ±1% current accuracy and self-diagnostics.
Core Protective Functions
- Continuous Monitoring
- Tracks real-time current (0.5-600A range)
- Intelligent Delay
- Ignores harmless startup surges (5-15 sec)
- Instant Disconnection
- Trips within 0.1 sec during persistent overloads
- Flexible Reset Options
- Manual reset for safety-critical systems
- Automatic reset for continuous processes
Working Principles Explained
Thermal Relays:
Current → heats bimetal → curvature → mechanical trip → circuit break
Magnetic Relays:
Current → magnetic field → plunger activation → contact separation
Electronic Relays (CNC EOR Series):
CT sensors → signal processing → microcontroller analysis → solid-state tripping
Industry Applications
| Sector | Protection Scenario | CNC Solution |
|---|---|---|
| Manufacturing | Conveyor motors | voltage up to 690V, current up to 0.1-630A under 8-hours duty or uninterrupted duty. |
| HVAC | Compressors & blowers | Coordination with auto changeover switch during power transitions |
| Water Treatment | Pump motor overloads | Suitable for wet environments |
| Data Centers | Backup generator transfer | <100ms response with auto changeover switch systems |
Pricing & Selection Guide
| Relay Type | Price Range | Key Selection Factors |
|---|---|---|
| Thermal | $15-$50 | Trip class (10/20/30) |
| Magnetic | $40-$100 | Instantaneous trip setting |
| Electronic | $80-$200 | Communication protocols (Modbus/Profibus) |
CNC Advantage: 30% lower lifecycle cost vs. premium brands with equivalent IEC 60947-4-1 certification.
Critical Compatibility Notes
- Current Rating: Must exceed motor FLA by 125%
- Trip Class:
- Class 10: Standard equipment (10 sec trip at 600% load)
- Class 20: High-inertia loads
- System Integration:
- Verify compatibility with existing auto changeover switch controls
- Confirm voltage thresholds for coordinated protection
Why Engineers Specify CNC Relays
- Accuracy: Real-time thermal modeling prevents nuisance tripping
- Resilience: Withstands 50kA short-circuit currents
- Smart Features:
- Predictive maintenance alerts
- Auto changeover switch synchronization
- Compliance: Full UL 508/CE documentation
Conclusion
Overload relays remain non-negotiable for motor protection across industries. When selecting relays:
- Prioritize electronic types for critical infrastructure
- Ensure seamless integration with auto changeover switch systems
- Validate certifications (IEC 60947-4-1, UL 508)
CNC’s engineered solutions deliver certified protection with reduced downtime through advanced diagnostics and auto changeover switch interoperability.
Post time: Jun-09-2025
