Overload Relay Classes: Class 10 vs. Class 20 Explained for Motor Protection

The difference between class 10 and class 20 overload relay systems lies in their response timing during motor overload conditions. Class 10 relays trip within 10 seconds at 600% current, while Class 20 relays allow up to 20 seconds, providing different levels of motor protection for varying applications.

Understanding Overload Relay Trip Classes

Trip classes show how many seconds an overload breaker will handle high current before shutting off the motor. This system helps engineers pick the right protection for different motors and applications.

The standard test measures how relays respond when carrying 600% (six times) the motor’s normal current. This extreme condition simulates overload situations that could damage motor parts without proper protection.

Which is a Classification of Overload Relays?

Standard thermal overload relay classes include 5, 10, 20, and 30. Each number shows the maximum trip time in seconds at 600% current. Class 5 responds fastest for very sensitive equipment, while Class 30 handles very heavy starting loads.

Modern electronic overload relays often let you select different trip classes in one device. For applications requiring maximum precision and flexibility, solid state overload relay technology offers electronic accuracy beyond traditional thermal protection methods, with programmable trip classes and enhanced monitoring capabilities.

Class 10 vs Class 20 Comparison

Response Time Differences

Class 10 relays protect faster by tripping within 10 seconds at high current. This works well for motors that can’t handle long overcurrent periods. Class 20 relays wait up to 20 seconds, which helps motors with higher heat capacity and longer startup times.

Application Suitability

Class 10 works best for fans, precision equipment, and motors with forced cooling where heat builds up quickly. Class 20 suits heavy machines like conveyors and crushers that need more time to reach normal speed.

Protection vs Smooth Operation

Class 10 gives maximum motor protection but might trip unnecessarily on heavy loads. Class 20 balances protection with smooth operation, reducing unwanted shutdowns during normal startup.

What is a Class 10 Overload Relay?

A Class 10 overload relay provides fast protection by tripping within 10 seconds during serious overload conditions. This quick response works well for motors that heat up fast or use artificial cooling systems.

Class 10 relays excel in precision machinery, lab equipment, and motors with sensitive cooling systems. The faster tripping prevents heat damage in motors that can’t handle long overcurrent periods.

Class 20 Overload Relay Applications

Class 20 relays wait up to 20 seconds before tripping, giving motors with heavy starting loads more time. This longer timing prevents unwanted trips when normal startup current stays high for 10-15 seconds.

Heavy applications like conveyors, crushers, and large pumps benefit from Class 20 protection. These motors often take longer to start up, and early tripping would cause unnecessary shutdowns.

How to Choose an Overload Relay?

Motor type drives your choice. Motors with artificial cooling or low heat capacity need Class 10 protection for quick response. Standard motors with natural cooling can usually use Class 20 relays.

Application needs matter too. Heavy loads that take time to accelerate need Class 20 or higher classes. Quick-starting applications with light loads work well with Class 10 protection.

Simply Buy’s technical team helps navigate these choices across leading brands like ABB, Schneider, and Siemens. We check motor specs, load types, and operating needs to recommend the best protection levels.

Cold vs Hot State Considerations

Trip behavior changes between cold starts and hot restarts. Cold motors need more heating time before thermal elements reach trip temperature. Hot motors from recent operation trip faster due to higher starting temperatures.

Applications with frequent starts and stops must consider hot-state behavior to prevent unwanted tripping. Motors that cycle regularly operate closer to hot-state trip curves, requiring careful relay selection.

Professional Selection Guidance

Simply Buy’s supplier network provides access to Class 10 and Class 20 models from multiple premium brands including ABB, Schneider, Siemens, and Eaton. Our partnerships ensure authentic products meeting North American and European industrial standards.

We resolve cross-brand purchasing challenges when projects require different manufacturers’ components. Whether you need ABB Class 10 relays for precision applications or Schneider Class 20 units for heavy-duty conveyors, we provide complete product ranges from verified suppliers.

We analyze your specific motor requirements to help you choose the right motor controller and integrate overload protection with your control system. The choice between Class 10 and Class 20 depends on balancing motor protection against smooth operation.