There are a great many circuit protection specifications and specification writing agencies that have an impact on the manufacturer and user. They range from the U.S. military to international agencies like IEC. Key specifications are regulatory agency Underwriters Laboratories’ (UL) Standards for Safety for low-voltage overcurrent protection devices. The differences in UL services related to circuit protection devices and the requirements and test parameters of UL 489 – the standard for Molded-Case Circuit Breakers, and UL 1077 – the standard for Supplementary Protectors for Use in Electrical Equipment are compared. 

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UL489 and UL1077

The focus of this MP Technical Brief is the regulatory agency Underwriters Laboratories’ (UL) Standards for Safety for low-voltage overcurrent protection devices. As such, we will review the differences in UL services related to circuit protection devices by comparing the requirements and test parameters of UL 489 – the standard for Molded-Case Circuit Breakers, and UL 1077 – the standard for Supplementary Protectors for Use in Electrical Equipment.

Under the standards of UL, most circuit protection devices are investigated and covered by UL’s Recognition or Listing services. In both cases follow-up services are used to insure continued compliance.

Under the UL services, Molded-Case Circuit Breakers are evaluated and “Listed” to UL 489 for use as a standalone product and the UL follow-up service tests the devices (typically 2-4 times per year) to the original test specification.

By contrast, “Recognized” devices under UL 1077, Supplementary Protectors for Use in Electrical Equipment, are evaluated only for use as components in Listed products, with the UL follow-up service checking to ensure that the materials and design used in manufacture remains consistent with the original Recognized device.

UL 489 and UL 1077 require the same general types of testing. However, the severity of the test parameters varies with intended use and standard under which a device is covered. To limit the scope of this paper, only the general testing required by these standards will be addressed. For deeper insight, the reader may obtain copies of UL 489 and UL1077 from UL.

While the order of testing may vary with the standard, Table 1 of the technical brief presents the requirements for each standard, UL 489 and UL 1077. Devices with optional features, such as auxiliary contacts, require additional testing.

Download the full technical brief for the table 1 test information as well as the impact of manufacturer specified protector parameters.  Get the full technical brief here