In and, ANSI Device Numbers can be used to identify equipment and devices in a system such as,, or. The device numbers are enumerated in In and, ANSI Device Numbers can be used to identify equipment and devices in a system such as,, or. The device numbers are enumerated in / Standard C37.2 Standard for Electrical Power System Device Function Numbers, Acronyms, and Contact Designations. Many of these devices protect electrical systems and individual system components from damage when an unwanted event occurs such as an. Historically, a single protective function was performed by one or more distinct devices, so each device would receive its own number. Today, -based relays can perform many protective functions in one device. • 1 - Master Element• 2 - Time-delay Starting or Closing Relay• 3 - Checking or Interlocking Relay, complete Sequence• 4 - Master Protective• 5 - Stopping Device, Emergency Stop Switch• 6 - Starting Circuit Breaker• 7 - Rate of Change Relay• 7F - Alternative number for Rate Of Change Of Frequency Relay ()• 8 - Control Power Disconnecting Device• 9 - Reversing Device• 10 - Unit Sequence Switch• 11 - Multifunction Device• 12 - Overspeed Device• 13 - Synchronous-Speed Device• 14 - Underspeed Device• 15 - Speed or Frequency Matching Device• 16 - Data Communications Device• 17 - Shunting or Discharge Switch• 18 - Accelerating or Decelerating Device• 19 - Starting-to-Running Transition Contactor• 20 - Electrically-Operated Valve (Solenoid Valve)• 21 - Distance Relay• 21G - Ground Distance• 21P - Phase Distance• 22 - Equalizer Circuit Breaker• 23 - Temperature control device, Heater• 24 - Volts per Hertz Relay (in some old analog applications, a 59 and an 81 device would be chained together as a 59/81 to implement the equivalent of V/Hz protection)A suffix letter or number may be used with the device number; for example, suffix N is used if the device is connected to a Neutral wire (example: 59N in a relay is used for protection against Neutral Displacement); and suffixes X, Y, Z are used for auxiliary devices. Similarly, the "G" suffix can denote a "ground", hence a "51G" is a time overcurrent ground relay. The "G" suffix can also mean "generator", hence an "87G" is a Generator Differential Protective Relay while an "87T" is a Transformer Differential Protective Relay. "F" can denote "field" on a generator or "fuse", as in the protective fuse for a pickup transformer. Suffix numbers are used to distinguish multiple "same" devices in the same equipment such as 51–1, 51–2. Device numbers may be combined if the device provides multiple functions, such as the Instantaneous / Time-delay relay denoted as 50/51. For device 16, the suffix letters further define the device: the first suffix letter is 'S' for serial or 'E' for Ethernet. The subsequent letters are: 'C' security processing function (e.g. VPN, encryption), 'F' firewall or message filter, 'M' network managed function, 'R' rotor, 'S' switch and 'T' telephone component. Thus a managed Ethernet switch would be 16ESM.
