It includes 99 device functions numbered 1 through 99 with descriptions such as master element, time-delay starting or closing relay, AC time overcurrent relay, AC circuit breaker, exciter or DC generator relay, and machine or transformer thermal relay. In electric power systems and industrial automation, ANSI Device Numbers can be used to identify equipment and devices in a system such as relays, circuit breakers, or instruments. The device numbers are enumerated in ANSI / IEEE Standard C37. These numbers are based on a system that is adopted by a standard for automatic switchgear by Institute of Electrical. The widely used United Sates standard ANSI/IEEE C37. Even in those parts of the world where IEC standards are predominate, the use of ANSI numbering. Understanding power system protection requires familiarity with ANSI standard relay numbers. Utility companies rely on these numbers for clear.
[PDF Version]