Miniature Circuit Breakers/Supplemental Protectors

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High Density Supplementary Protectors (Miniature Circuit Breakers)

Introduction Standards Compliance and Certifications Applications Cat. No. Explanation Product Selection Specifications Approximate Dimensions
Application Information

UL 1077, CSA C22.2 #235

In North America, miniature circuit breakers are recognized as supplementary protectors and are intended for use as overcurrent protection within an appliance or other electrical equipment where branch circuit protection is already provided or not required. Internationally, these products are rated to IEC standards as circuit breakers for equipment (CBE).

Selection Information

High-density supplementary protector/miniature circuit breaker applications include, but are not limited to, the protection of test equipment, control instrumentation, solenoids, and power supplies. The wide range of current values and the use of a thermal magnetic trip system allows for a variety of applications where a very accurate and compact breaker is required.

To select a miniature circuit breaker, use the following procedure:
1. Determine the inrush correction factor from the following table.

Inrush Ratio Correction Table
Inrush Ratio 1:1 to 1:4 1:5 1:6 1:7 1:8
Factor 1.3 1.4 1.5 1.6 1.7

Note:For resistive loads use an inrush correction factor of 1.0.

2. Determine the temperature correction factor from the following table.

Ambient Temperature Correction Table
Ambient Temperature 70 °F
(21.1 °C)
100 °F
(37.8 °C)
120 °F
(48.9 °C)
140 °F
(60 °C)
160 °F
(71.1 °C)
180 °F
(82.2 °C)
200 °F
(93.3 °C)
Factor 1.0 1.1 1.2 1.3 1.4 1.5 1.6

3. Determine the sealed current of the load being protected.

4. Multiply the sealed current by the two correction factors and select the closest higher ampere rating.

Example — For a solenoid with sealed current of 0.5 A, an inrush ratio of 1:8, and an ambient temperature of +110 °F, (0.5 x 1.7 x 1.15 = 0.9775), select the 1.0 A miniature circuit breaker. Tripping time of the miniature circuit breaker is determined from the table below. Divide the miniature circuit breaker value by the temperature correction factor from the Ambient Temperature Correction Table to determine the actual rated current referenced in the table below.

Tripping Times in Seconds at 70 °F (21.1 °C)
Percent Rated
100% 200% 300% 400% 500% 600% 1000% 2000%
Tripping Times
No Trip 10…40 3…18 1.5…9 0.8…6 0.003…4 0.009…2 Max.

Note: When several breakers are rail mounted adjacent to each other, the no-trip current will be 80% of rated current at 70 °F (21.1 °C).