Differences in UL1077 Overload (OL) Performance Ratings – How to Choose the Right Supplementary Protector
In the safety design of electrical and electronic equipment, overload protection is essential. UL1077, the international standard for Supplementary Protectors (SPs), defines how protective devices should perform under various overload conditions.
Among these requirements, the Overload (OL) test codes are critical performance indicators. They differentiate the levels of overload capability and help engineers, designers, and end users select the most suitable device for their applications.
What Are OL Test Codes in UL1077?
UL1077 defines several levels of overload performance. Common OL codes include:
- • OL0：Basic level, able to withstand short-duration, light overloads.
- • OL1：Can withstand moderate overloads for a specific duration.
- • OL2 / OL3：Provide higher multiples or longer-duration overload protection, ideal for demanding current conditions.
- • OL4 / OL5：Typically used in industrial-grade equipment, ensuring reliable tripping even under long-term heavy loads.
These OL ratings show whether a supplementary protector can trip reliably and protect equipment under the combined effect of overload current × duration.
Why Choosing the Correct OL Rating Is Important
The overload rating of a UL1077 protector is more than just a number—it directly impacts equipment safety, reliability, and maintenance costs.
- • Accurate Protection: Avoids nuisance tripping or insufficient protection caused by current fluctuations.
- • Extended Service Life: Reduces premature wear or frequent tripping.
- • Regulatory Compliance: Certain industries (e.g., North American industrial equipment) require specific OL ratings.
- • Reduced Maintenance Costs: Correct OL rating minimizes downtime due to unnecessary tripping or device failure.
UL1077 OL0 vs. OL1 Comparison
| Category | OL0（General Use） | OL1（Motor Starting Applications） |
| Test Condition | 1.5 × rated current | AC: 6 × rated current DC: 10 × rated current |
| Durability Requirement | Must withstand 50 on-off cycles without failure | Must withstand 50 on-off cycles without failure |
| Application Range | General electronics, low-power devices | Motors, pumps, compressors, HVAC systems |
| Contact Material | Standard contacts, cost-effective | Silver metal oxide contacts, withstand high inrush current |
| Feature | Economical, sufficient for most uses | Reliable under inrush current, higher cost |
| Risk of Misapplication | If used in motor applications, contacts may weld, causing overload or fire risk | Proper for motor applications, withstands inrush currents safely |
In short, OL0 is best for general electronics, while OL1 is designed for motor starting applications where inrush current is high.
Practical Guidelines for Selecting OL Ratings
Choosing the right UL1077 overload rating depends on the type of equipment:
- • Household / Low-Power Applications → OL0 ~ OL1 is sufficient.
- • Commercial Equipment / Electronics → OL1 ~ OL2 for balanced protection and durability.
- • Industrial / Motor Equipment →OL2 or higher ensures long-term stable operation.
- • High-Risk Applications (UPS, welding machines, etc.) → OL3 ~ OL5 for maximum reliability and safety
Conclusion
The Overload Performance Rating (OL) in UL1077 is a critical factor in the selection of supplementary protectors:
- • OL0 – cost-effective, suitable for general electronics.
- • OL1 and above – designed for motor starting or high inrush current conditions.
By selecting the correct OL rating, users can:
- • Avoid nuisance tripping or insufficient protection
- • Improve system reliability
- • Extend equipment life
- • Reduce risks caused by misapplication
The right UL1077 OL rating is the best guarantee of safe, reliable, and cost-effective equipment operation.
Frequently Asked Questions (FAQ)
Q1: What is the difference between UL1077 and UL489?
A：UL1077 Supplementary Protectors are designed to provide additional protection within equipment, but they cannot replace branch circuit protection. On the other hand, UL489 Circuit Breakers are rated for full branch circuit protection, offering higher interrupting capacity and the ability to serve as the primary protective device in electrical installations.
Q2: What happens if I use the wrong OL rating?
A：Applying the wrong overload rating can cause serious issues. For example, using OL0 in motor applications may result in contact welding, leading to overload or even fire hazards. Conversely, choosing an OL rating that is too high can delay protection, reduce system safety, and compromise equipment reliability.
Q3: How do I know which UL1077 OL rating to choose?
A：The correct UL1077 OL rating depends on the type of load and application. General electronic devices may only require OL0, while motors or equipment with high inrush current often need OL1 or higher. Industrial and high-risk equipment may require OL2 to OL5. When in doubt, it is best to follow the manufacturer’s guidelines or consult a technical expert to ensure safe and reliable operation.
If you have questions about UL1077 overload ratings, OL0 vs. OL1 differences, or need support in selecting the right supplementary protector for your application, please contact KUOYUH for professional assistance.
