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Common-Circuit-Slide30

For example, UL 489 requires interrupting capacity from 5000 Amps and above. While perfectly appropriate for main power distribution applications, this standard has been perpetuated in other industries- where short circuit ratings governed by circuit resistance, is much lower. The UL 1077 standard for supplementary protectors covers the short circuit test and lists the current at which the breaker was tested. Although certain devices, such as UL 489 molded case circuit breakers, have higher interrupting capacities, they may not be well suited for lower current applications where precise overload protection and adequate short circuit protection is better provided by UL 1077 supplementary protector.

PTM Published on: 2011-10-27