The essential specifications of overcurrent protection devices (commonly called  “Circuit Breakers”) are covered by Underwriters Laboratories standards UL 489 Molded-Case Circuit Breakers and UL 1077 Supplementary Protectors for Use in Electrical Equipment.

While both standards require that devices are investigated for continuing compliance, the standards differ in performance expectations and follow-up services. UL 489 and UL 1077 “Listing” and “Recognition” marks denote some of these differences.

Without a clear understanding of the requirement/performance differences between a “Circuit Breaker” and a “Supplementary Protector”, dangerous misapplications may result.

For detailed information on the differences in these performance requirements and UL follow up services please refer to MP Technical Brief, Article 2.0 UL Circuit Breaker Standards Comparison – UL 489 vs. UL 1077.