·   51V – Voltage Restrained Time Overcurrent

·   51Q – Negative Sequence Time Overcurrent

·   52 – AC circuit breaker

·   52a – AC circuit breaker position (contact open when circuit breaker open)

·   52b – AC circuit breaker position (contact closed when circuit breaker open)

·   53 – Exciter or Dc Generator Relay

·   54 – Turning Gear Engaging Device

·   55 – Power Factor Relay

·   56 – Field Application Relay

·   57 – Short-Circuiting or Grounding Device

·   58 – Rectification Failure Relay

·   59 – Overvoltage Relay

·   59B – Bank Phase Overvoltage

·   59P – Phase Overvoltage

·   59N – Neutral Overvoltage

·   59NU – Neutral Voltage Unbalance

·   59P – Phase Overvoltage

·   59X – Auxiliary Overvoltage

·   59Q – Negative Sequence Overvoltage

·   60 – Voltage or Current Balance Relay

·   60N – Neutral Current Unbalance

·   60P – Phase Current Unbalance

·   61 – Density Switch or Sensor

·   62 – Time-Delay Stopping or Opening Relay

·   63 – Pressure Switch Detector

·   64 – Ground Protective Relay

·   64F – Field Ground Protection

·   64R

– Rotor earth fault

·   64REF – Restricted earth fault differential

·   64S – Stator earth fault

·   64S – Sub-harmonic Stator Ground Protection

·   64TN – 100% Stator Ground

·   65 – Governor

·   66 – Notching or Jogging Device/Maximum Starting Rate/Starts Per Hour/Time Between Starts

·  67 – AC Directional Overcurrent Relay

·   67G – Ground Directional Overcurrent

·   67N – Neutral Directional Overcurrent

·   67Ns – Earth fault directional

·   67P – Phase Directional Overcurrent

·   67SG – Sensitive Ground Directional Overcurrent

·   67Q – Negative Sequence Directional Overcurrent

·   68 – Blocking Relay / Power Swing Blocking

·   69 – Permissive Control Device

·   70 – Rheostat

·   71 – Liquid Switch, Level Switch

·   72 – DC Circuit Breaker

·   73 – Load-Resistor Contactor

·   74 – Alarm Relay

·   75 – Position Changing Mechanism

·   76 – DC Overcurrent Relay

·   77 – Telemetering Device, Speed Sensor

·   78 – Phase Angle Measuring or Out-of-Step Protective Relay

·   78V – Loss of Mains

·   79 – AC Reclosing Relay / Auto Reclose

·   80 – Liquid or Gas Flow Relay

·   81 – Frequency Relay

·   81O – Over Frequency

·   81R – Rate-of-Change Frequency

·   81U – Under Frequency

·   82 – DC Reclosing Relay

·   83 – Automatic Selective Control or Transfer Relay

·   84 – Operating Mechanism

·   85 – Pilot Communications, Carrier or Pilot-Wire Relay

·   86 – Lock-Out Relay, Master Trip Relay

·   87 – Differential Protective Relay

·   87B – Bus Differential

·   87G – Generator Differential

·   87GT – Generator/Transformer Differential

·   87L – Segregated Line Current Differential

·   87LG – Ground Line Current Differential

·   87M – Motor Differential

·   87O – Overall Differential

·   87PC – Phase Comparison

·   87RGF – Restricted Ground Fault

·   87S – Stator Differential

·   87S – Percent Differential

·   87T – Transformer Differential

·   87V – Voltage Differential

·   88 – Auxiliary Motor or Motor Generator

·   89 – Line Switch

·   90 – Regulating Device

·   91 – Voltage Directional Relay

·   92 – Voltage And Power Directional Relay

·   93 – Field-Changing Contactor

·   94 – Tripping or Trip-Free Relay

·   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

·   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

·   25 – Synchronizing or synchronism-check device

·   26 – Apparatus thermal device, Temperature Switch

·   27 – Undervoltage relay

·   27P – Phase Undervoltage

·   27S – DC undervoltage relay

·   27TN – Third Harmonic Neutral Undervoltage

·   27TN/59N – 100% Stator Earth Fault

·   27X – Auxiliary Undervoltage

·   27 AUX – Undervoltage Auxiliary Input

·   27/27X – Bus/Line Undervoltage

·   27/50 – Accidental Generator Energization

·   28 – Flame Detector

·   29 – Isolating Contactor

·   30 – Annunciator Relay

·   31 – Separate Excitation Device

·   32 – Directional Power Relay

·   32L – Low Forward Power

·   32H – High Directional Power

·   32N – Wattmetric Zero-Sequence Directional

·   32P – Directional Power

·   32R – Reverse Power

·   33 – Position Switch

·   34 – Master Sequence Device

·   35 – Brush-Operating or Slip-ring Short Circuiting Device

·   36 – Polarity or Polarizing Voltage Device

·   37 – Undercurrent or Underpower Relay

·   37P – Underpower

·   38 – Bearing Protective Device / Bearing Rtd

·   39 – Mechanical Condition Monitor ( Vibration )

·   40 – Field Relay / Loss of Excitation

·   41 – Field Circuit Breaker

·   42 – Running Circuit Breaker

·   43 – Manual Transfer or Selector Device

·   44 – Unit Sequence Starting Relay

·   45 – Fire Detector

·   46 – Reverse-Phase or Phase Balance Current Relay or Stator Current Unbalance

·   47 – Phase-Sequence or Phase Balance Voltage Relay

·   48 – Incomplete Sequence Relay / Blocked Rotor

·   49 – Machine or Transformer Thermal Relay / Thermal Overload

·   49RTD – RTD Biased Thermal Overload

·   50 – Instantaneous Overcurrent Relay

·   50BF – Breaker Failure or LBB ( Local Breaker Back-up )

·   50DD – Current Disturbance Detector

·   50EF – End Fault Protection

·   50G – Ground Instantaneous Overcurrent

·   50IG – Isolated Ground Instantaneous Overcurrent

·   50LR – Acceleration Time

·   50N – Neutral Instantaneous Overcurrent

·   50NBF – Neutral Instantaneous Breaker Failure

·   50P – Phase Instantaneous Overcurrent

·   50SG – Sensitive Ground Instantaneous Overcurrent

·   50SP – Split Phase Instantaneous Current

·   50Q – Negative Sequence Instantaneous Overcurrent

·   50/27 – Accidental Energization

·   50/51 – Instantaneous / Time-delay Overcurrent relay

·   50/74 – Ct Trouble

·   50/87 – Instantaneous Differential

·   51 – AC Time Overcurrent Relay

·   51G – Ground Time Overcurrent

·   51LR – AC inverse time overcurrent (locked rotor) protection relay

·   51N – Neutral Time Overcurrent

·   51P – Phase Time Overcurrent

·   51R – Locked / Stalled Rotor