Measuring molded case circuit breaker resistance

Molded case circuit breaker resistance is measured under various conditions to demonstrate the need for more standardized procedures when performing millivolt drop measurements. Breakers, rated at 600 V/sub ac//250 A/sub ac/ and 120/240 V/sub ac//50 A/sub ac/, with silver-tungsten (Ag-W) contacts are used to show that contact resistance can cause variability in circuit breaker resistance and to demonstrate the influence of current, time, contact temperature, and applied voltage on contact resistance. Based on these results, guidelines are developed for making reliable resistance measurements on molded-case circuit breakers (MCCB) when using the millivolt drop technique.<
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