ANSI-IEEE DEVICE NUMBERS  32N - Watt metric Zero-Sequence Directional

 32P - Directional Power

In the design of electrical power systems,  32R - Reverse Power
the ANSI standard device  33 - Position Switch
numbers (ANSI /IEEE Standard C37.2 Standard for  34 - Master Sequence Device
Electrical Power System Device Function Numbers,  35 - Brush-Operating or Slip-ring Short
Acronyms, and Contact Designations ) identifies the Circuiting Device
features of a protective device such as a relay or circuit  36 - Polarity or Polarizing Voltage Device
breaker. These types of devices protect electrical  37 - Undercurrent or Underpower Relay
systems and components from damage when an  37P - Underpower
unwanted event occurs, such as an electrical fault.  38 - Bearing Protective Device / Bearing Rtd
Device numbers are used to identify the functions of  39 - Mechanical Condition Monitor (Vibration)
devices shown on a schematic diagram. Function  40 - Field Relay / Loss of Excitation
descriptions are given in the standard.  41 - Field Circuit Breaker
 42 - Running Circuit Breaker
 43 - Manual Transfer or Selector Device
One physical device may correspond to one function
 44 - Unit Sequence Starting Relay
number, for example "29 Isolating Contactor", or a
 45 - Atmospheric Condition Monitor (fumes,
single physical device may have many function
smoke, fire)
numbers associated with it, such as a
 46 - Reverse-Phase or Phase Balance Current
numerical protective relay. Suffix and prefix letters
Relay or Stator Current Unbalance
may be added to further specify the purpose and
 47 - Phase-Sequence or Phase Balance Voltage
function of a device.
Relay
 48 - Incomplete Sequence Relay / Blocked
ANSI/IEEE C37.2-2008 is one of a continuing series of Rotor
revisions of the standard, which originated in 1928  49 - Machine or Transformer Thermal Relay /
as American Institute of Electrical Engineers Standard Thermal Overload
No. 26.  49RTD - RTD Biased Thermal Overload
 50 - Instantaneous Overcurrent Relay
LIST OF DEVICE NUMBERS AND ACRONYMS  50BF - Breaker Failure or LBB (Local Breaker
Back-up)
 1 - Master Element
 50DD - Current Disturbance Detector
 2 - Time-delay Starting or Closing Relay
 50EF - End Fault Protection
 3 - Checking or Interlocking Relay, complete
 50G - Ground Instantaneous Overcurrent
Sequence  50IG - Isolated Ground Instantaneous
Overcurrent
 4 - Master Protective
 5 - Stopping Device, Emergency Stop Switch
 50LR - Acceleration Time
 6 - Starting Circuit Breaker
 50N - Neutral Instantaneous Overcurrent
 7 - Rate of Change Relay
 50NBF - Neutral Instantaneous Breaker Failure
 8 - Control Power Disconnecting Device
 50P - Phase Instantaneous Overcurrent
 9 - Reversing Device
 50SG - Sensitive Ground Instantaneous
Overcurrent
 10 - Unit Sequence Switch
 11 - Multifunction Device
 50SP - Split Phase Instantaneous Current
 12 - Overspeed Device
 50Q - Negative Sequence Instantaneous
Overcurrent
 13 - Synchronous-Speed Device
 14 - Under Speed Device
 50/27 - Accidental Energization
 15 - Speed or Frequency Matching Device
 50/51 - Instantaneous / Time-delay Overcurrent
relay
 16 - Data Communications Device
 17 - Shunting or Discharge Switch
 50/74 - Ct Trouble
 18 - Accelerating or Decelerating Device
 50/87 - Instantaneous Differential
 19 - Starting-to-Running Transition Contactor
 51 - AC Time Overcurrent Relay
 20 - Electrically-Operated Valve (Solenoid
 51G - Ground Time Overcurrent
Valve)
 51LR - AC inverse time overcurrent (locked
rotor) protection relay
 21 - Distance Relay
 21G - Ground Distance
 51N - Neutral Time Overcurrent
 21P - Phase Distance
 51P - Phase Time Overcurrent
 22 – Equalizer circuit breaker
 51R - Locked / Stalled Rotor
 23 – Temperature control device, Heater
 51V - Voltage Restrained Time Overcurrent
 24 – Volts per hertz relay
 51Q - Negative Sequence Time Overcurrent
 25 – Synchronizing or synchronism-check
 52 – AC circuit breaker
device
 52a - AC circuit breaker position (contact open
when circuit breaker open)
 26 – Apparatus thermal device, Temperature
Switch
 52b - AC circuit breaker position (contact
closed when circuit breaker open)
 27 – Undervoltage relay
 27P - Phase Undervoltage
 53 - Exciter or Dc Generator Relay
 27S - DC undervoltage relay
 54 - Turning Gear Engaging Device
 27TN - Third Harmonic Neutral Undervoltage
 55 - Power Factor Relay
 27TN/59N - 100% Stator Earth Fault
 56 - Field Application Relay
 27X - Auxiliary Undervoltage
 57 - Short-Circuiting or Grounding Device
 27 AUX - Undervoltage Auxiliary Input
 58 - Rectification Failure Relay
 27/27X - Bus/Line Undervoltage
 59 - Overvoltage Relay
 27/50 - Accidental Generator Energization
 59B - Bank Phase Overvoltage
 28 - Flame Detector
 59N - Neutral Overvoltage
 29 - Isolating Contactor
 59NU - Neutral Voltage Unbalance
 30 - Annunciator Relay
 59P - Phase Overvoltage
 31 - Separate Excitation Device
 59X - Auxiliary Overvoltage
 32 - Directional Power Relay
 59Q - Negative Sequence Overvoltage
 32L - Low Forward Power
 60 - Voltage or Current Balance Relay
 32H - High Directional Power
 60N - Neutral Current Unbalance
 60P - Phase Current Unbalance
 61 - Density Switch or Sensor
 62 - Time-Delay Stopping or Opening Relay
 63 - Pressure Switch Detector ACRONYMS DESCRIPTION
 64 - Ground Protective Relay
 64F - Field Ground Protection
 64R – Rotor earth fault  AFD - Arc Flash Detector
 64REF – Restricted earth fault differential  CLK - Clock or Timing Source
 64S – Stator earth fault  CLP - Cold Load Pickup
 64S - Sub-Harmonic Stator Ground Protection  DDR – Dynamic Disturbance Recorder
 64TN - 100% Stator Ground  DFR – Digital Fault Recorder
 65 - Governor  DME – Disturbance Monitor Equipment
 66 - Notching or Jogging Device/Maximum  ENV – Environmental data
Starting Rate/Starts Per Hour/Time Between  HIZ – High Impedance Fault Detector
Starts  HMI – Human Machine Interface
 67 - AC Directional Overcurrent Relay  HST – Historian
 67G - Ground Directional Overcurrent  LGC – Scheme Logic
 67N - Neutral Directional Overcurrent  MET – Substation Metering
 67Ns – Earth fault directional  PDC – Phasor Data Concentrator
 67P - Phase Directional Overcurrent  PMU – Phasor Measurement Unit
 67SG - Sensitive Ground Directional  PQM – Power Quality Monitor
Overcurrent  RIO – Remote Input/output Device
 67Q - Negative Sequence Directional  RTD - Resistance Temperature Detector
Overcurrent  RTU – Remote Terminal Unit/Data Concentrator
 68 - Blocking Relay / Power Swing Blocking  SER – Sequence of Events Recorder
 69 - Permissive Control Device  TCM – Trip Circuit Monitor
 70 - Rheostat  LRSS – Local/Remote selector switch
 71 - Liquid Switch, Level Switch  VTFF - Vt Fuse Fail
 72 - DC Circuit Breaker
 73 - Load-Resistor Contactor
 74 - Alarm Relay
 75 - Position Changing Mechanism SUFFIXES DESCRIPTION
 76 - DC Overcurrent Relay
 77 - Telemetering Device, Speed Sensor
 78 - Phase Angle Measuring or Out-of-Step  _1 - Positive-Sequence
Protective Relay  _2 - Negative-Sequence
 78V - Loss of Mains  A - Alarm, Auxiliary Power
 79 - AC Reclosing Relay / Auto Reclose  AC - Alternating Current
 80 - Liquid or Gas Flow Relay  AN - Anode
 81 - Frequency Relay  B - Bus, Battery, or Blower
 81O - Over Frequency  BF - Breaker Failure
 81R - Rate-of-Change Frequency  BK - Brake
 81U - Under Frequency  BL - Block (Valve)
 82 - DC Reclosing Relay  BP - Bypass
 83 - Automatic Selective Control or Transfer  BT - Bus Tie
Relay  BU - Backup
 84 - Operating Mechanism  C - Capacitor, Condenser, Compensator, Carrier
 85 - Pilot Communications, Carrier or Pilot-Wire Current, Case or Compressor
Relay  CA - Cathode
 86 - Lock-Out Relay, Master Trip Relay  CH - Check (Valve)
 87 - Differential Protective Relay  D - Discharge (Valve)
 87B - Bus Differential  DC - Direct Current
 87G - Generator Differential  DCB - Directional Comparison Blocking
 87GT - Generator/Transformer Differential  DCUB - Directional Comparison Unblocking
 87L - Segregated Line Current Differential  DD - Disturbance Detector
 87LG - Ground Line Current Differential  DUTT - Direct Underreaching Transfer Trip
 87M - Motor Differential  E - Exciter
 87O - Overall Differential  F - Feeder, Field, Filament, Filter, or Fan
 87PC - Phase Comparison  G - Ground or Generator
 87RGF - Restricted Ground Fault  GC - Ground Check
 87S - Stator Differential  H - Heater or Housing
 87S - Percent Differential  L - Line or Logic
 87T - Transformer Differential  M - Motor or Metering
 87V - Voltage Differential  MOC - Mechanism Operated Contact
 88 - Auxiliary Motor or Motor Generator  N - Neutral or Network
 89 - Line Switch  O - Over
 90 - Regulating Device  P - Phase or Pump
 91 - Voltage Directional Relay  PC - Phase Comparison
 92 - Voltage and Power Directional Relay  POTT - Pott: Permissive Overreaching Transfer
 93 - Field-Changing Contactor Trip
 94 - Tripping or Trip-Free Relay  PUTT - Putt: Permissive Underreaching Transfer
 95 – For specific applications where other Trip
numbers are not suitable  R - Reactor, Rectifier, or Room
 96 – Transmitter  S - Synchronizing, Secondary, Strainer, Sump,
 97 – For specific applications where other or Suction (Valve)
numbers are not suitable  SOTF - Switch On to Fault
 98 – For specific applications where other  T - Transformer or Thermatron
numbers are not suitable  TD - Time Delay
 99 – For specific applications where other  TDC - Time-Delay Closing Contact
numbers are not suitable  TDDO - Time Delayed Relay Coil Drop-Out
 TDO - Time-Delay Opening Contact
  TDPU - Time Delayed Relay Coil Pickup
 THD - Total Harmonic Distortion
 TH - Transformer (High-Voltage Side)
 TL - Transformer (Low-Voltage Side)
 TM - Telemeter
 TT - Transformer (Tertiary-Voltage Side)
 Q - Lube Oil
 W - Water
 F - Fuel
 G - Gas
 U - Under or Unit
 X - Auxiliary
 Z – Impedance

SUFFIXES AND PREFIXES

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 Overcurrent 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.