Protection Devices

• 12 – Overspeed Device
• 14 – Underspeed Device
• 21 – Distance Relay
• 25 – Synchronizing or Synchronism-Check Device
• 27 – Undervoltage Relay
• 32 – Directional Power Relay
• 37 – Undercurrent or Underpower Relay
• 38 – Bearing Protective Device
• 40 – Field (over/under excitation) Relay
• 46 – Reverse-phase or Phase-Balance Current Relay
• 47 – Phase-Sequence or Phase-Balance Voltage Relay
• 48 – Incomplete Sequence Relay
• 49 – Machine or Transformer, Thermal Relay
• 50 – Instantaneous Overcurrent Relay
• 50N – Instantaneous Overcurrent Relay (Earth Fault)
• 51 – AC Inverse Time Overcurrent Relay
• 51N – AC Inverse Time Overcurrent Relay (Earth Fault)
• 53 – Exciter or DC Generator Relay
• 55 – Power Factor Relay

• 56 – Field Application Relay
• 58 – Rectification Failure Relay
• 59 – Overvoltage Relay
• 60 – Voltage or Current Balance Relay
• 64 - Ground Detector Relay
• 67 – AC Directional Overcurrent Relay
• 68 – Blocking or "Out-of-Step" Relay
• 76 – DC Overcurrent Relay
• 79 – AC Reclosing Relay
• 81 – Frequency Relay
• 82 – DC Reclosing Relay
• 83 – Automatic Selective Control or Transfer Relay
• 85 – Communications,Carrier or Pilot-Wire Relay
• 86 – Lockout Relay
• 87 – Differential Protective Relay
• 91 – Voltage Directional Relay
• 92 – Voltage and Power Directional Relay
• 94 – Tripping or Trip-Free Relay

For the entire list of ANSI device numbers, refer to this Wikipedia page.