These codes, detailed in the IEEE C37. 2 standard, offer a standardized way to identify the function of protective relays and devices in electrical systems. Utility companies rely on these numbers for clear communication, while manufacturers design equipment adhering to this. The widely used United Sates standard ANSI/IEEE C37. One is given in ANSI Standard and uses a numbering system for various functions. ANSI IEEE Standard Device Numbers are below: (the more commonly used ones are in bold) 86T is a Lockout Relay for a. This handbook covers the code of practice in protection circuitry including standard lead and device numbers, mode of connections at terminal strips, colour codes in multicore cables, dos and donts in execution.