Device Number Definitionand function
1- 1 Master element
is the initiating device, such as a control switch, voltage relay, float switchetc., that serves either irectly, or through such permissive devices as protectiveand time-delay relays, to place an equipment
in or out of operation.
2- 2 Time-delay starting or closing relay
is a device that functions to give a desired amount of timedelay before or after any point of operation in a switching sequence or protectiverelay system, except as specifically
provided by device functions 48, 62 and 79 described later.
3- 3 Checking or interlocking relay
is a device that operates in response to the position of a number of otherdevices, (or to a number of predetermined conditions), in an equipment to allowan operating sequence to proceed,
to stop, or to provide a check of the position of thesedevices or of these conditions for any purpose.
4- 4 Master contactor
is a device, generally controlled by device No. 1 orequivalent, and the required permissive
and protective devices, that serve to make and break thenecessary control circuits to place an equipment into operation under thedesired conditions and to take it out of operation under
other or abnormal conditions.
5- 5 Stopping device
is a control device used primarily to shut down an equipmentand hold it out of operation. [This device may be manually or electricallyactuated, but excludes the function of
electrical lockout (see device function 86) on abnormalconditions.]
6- 6 Starting circuit breaker
is a device whose principal function is to connect amachine to its source of starting
voltage.
7- 7 Rate-of-rise relay
is a relay that functions on an excessive rate of riseof current.
8- 8 Control power disconnecting device
is a disconnecting device, such as a knife switch,circuit breaker, or pull-out fuse block, used for the purpose of respectivelyconnecting and disconnecting the source of control power to and from thecontrol bus or equipment.
9- 9 Reversing device
is used for the purpose of reversing a machine fieldor for performing any other reversing
functions.
10- 10 Unit sequence switch
is used to change the sequence in which units may beplaced in and out of service in
multiple-unit equipment.
11- 11 Multifunction device
is a device that performs three or more comparativelyimportant functions that could only be
designated by combining several of these device functionnumbers. All of the functions performed by device 11 shall be defined in thedrawing legend or device function list.
12- 12 Over speed device
is usually a direct connected speed switch thatfunctions on machine over speed.
13- 13 Synchronous-speed device
such as a centrifugal speed switch, a slip frequencyrelay, a voltage relay, an undercurrent relay, or any other type of device thatoperates at approximately the synchronous speed of a
machine.
14- 14 Under speed device
functions when the speed of a machine falls below apre-determined value.
15- 15 Speed or frequency matching device
functions to match and hold the speed or the frequency of amachine or of a system equal to, or approximately equal to, that of anothermachine, source, or system.
16- 16 Reserved for future application
17- 17 Shunting or discharge switch
serves to open or to close a shunting circuit around anypiece of apparatus (except a resistor), such as a machine field, a machine armature,a capacitor, or a reactor.
Note: This excludes devices that perform such shuntingoperations as may be necessary in the process of starting a machine by devices6 or 42, or their equivalent, and also excludes
device 73 function that serves for the switching ofresistors.
18- 18 Accelerating or decelerating device
is used to close or to cause the closing of circuitsthat are used to increase or decrease the speed of a machine.
19- 19 Starting-to-running transition
contactor is a device that operates to initiate or cause theautomatic transfer of a machine from the starting to the running powerconnection.
20- 20 Electrically operated valve
is an electrically operated, controlled, or monitoredvalve used in a fluid, air, gas, or vacuum line.
Note: The function of the valve may be indicated by the useof the suffixes, see page 11.
21- 21 Distance relay
is a relay that functions when the circuit admittance,impedance, or reactance increases or
decreases beyond a predetermined value.
22- 22 Equalizer circuit breaker
is a breaker that serves to control or to make andbreak the equalizer or the current balancing
connections for a machine field, or for regulatingequipment, in a multiple unit installation.
23- 23 Temperature control device
Functions to raise or to lower the temperature of amachine or other apparatus, or of any medium, when its temperature falls belowor rises above a predetermined value.
Note: An example is a thermostat that switches on a spaceheater in a switchgear assembly when the temperature falls to a desired valueas distinguished from a device that is used to provide automatic temperatureregulation between close limits and would be designated as 90T.
24- 24 Volts per hertz relay
is a relay that functions when the ratio of voltage tofrequency exceeds a preset value.
The relay may have an instantaneous or a timecharacteristic.
25- 25 Synchronizing or synchronism check
device operates when two ac circuits are within the desiredlimits of frequency, phase angle, or voltage to permit or to cause theparalleling of these two circuits.
26- 26 Apparatus thermal device
Functions when the temperature of the protectedapparatus (other than the loadcarrying
windings of machines and transformers as covered by devicefunction number 49) or of a liquid or other medium exceeds a predeterminedvalue; or when the temperature of the protected apparatus or of any mediumdecreases below a predetermined value.
27- 27 Under voltage relay
is a relay that operates when its input voltage isless than a predetermined value.
28- 28 Flame detector
is a device that monitors the presence of the pilot ormain flame in such apparatus as a gas
turbine or a steam boiler.
29- 29 Isolating contactor
is used expressly for disconnecting one circuit fromanother for the purposes of emergency
operation, maintenance, or test.
30 Annunciator relay
is a nonautomatically reset device that gives a numberof separate visual indications upon the functioning of protective devices andthat may also be arranged to perform a lock-out function.
31- 31 Separate excitation device
connects a circuit, such as the shunt field of a synchronousconverter, to a source of separate excitation during the starting sequence; orone which energizes the excitation and ignition
circuits of a power rectifier.
32- 32 Directional power relay
is a relay that operates on a predetermined value ofpower flow in a given direction or upon reverse power flow such as thatresulting from the motoring of a generator upon loss of its prime mover.
33- 33 Position switch
makes or breaks contact when the main device or pieceof apparatus that has no device function number reaches a given position.
34- 34 Master sequence device
is a device such as a motor operated multi contactswitch, or the equivalent, or a programming device, such as a computer, thatestablishes or determines the
operating sequence of the major devices in an equipmentduring starting
and stopping or during other sequential switchingoperations.
35- 35 Brush-operating or slip-ring shortcircuiting
device is used for raising, lowering or shifting the brushesof a machine; short-circuiting its slip rings; or engaging or disengaging thecontacts of a mechanical rectifier.
36- 36 Polarity or polarizing voltage device
operates, or permits the operation of, another device on apredetermined polarity only or that
verifies the presence of a polarizing voltage in anequipment.
37- 37 Undercurrent or under power relay
functions when the current or power flow decreases below apredetermined value.
38- 38 Bearing protective device
Functions on excessive bearing temperature or on otherabnormal mechanical conditions
associated with the bearing, such as undue wear, which mayeventually result in excessive bearing temperature or failure.
IEEE device numbers
39- 39 Mechanical condition monitor
is a device that functions upon the occurrence of anabnormal mechanical condition (except that associated with bearings as coveredunder device function 38), such as excessive vibration, eccentricity,expansion, shock, tilting, or seal failure.
40- 40 Field relay
functions on a given or abnormally low value orfailure of machine field current, or on an excessive value of the reactivecomponent of armature current in an ac machine indicating abnormally low fieldexcitation.
41- 41 Field circuit breaker
is a device that functions to apply or remove the fieldexcitation of a machine.
42- 42 Running circuit breaker
is a device whose principal function is to connect amachine to its source of running or
operating voltage. This function may also be used for adevice, such as a contactor, that is used in series with a circuit breaker orother fault protecting means, primarily for frequent opening and closing of thecircuit.
43- 43 Manual transfer or selector device
is a manually operated device that transfers the control circuitsin order to modify the plan of operation of the switching equipment or of someof the devices.
44- 44 Unit sequence starting relay
is a relay that functions to start the next availableunit in multiple unit equipment upon the failure or nonavailability of thenormally preceding unit.
45- 45 Atmospheric condition monitor
is a device that functions upon the occurrence of anabnormal atmospheric condition, such as damaging fumes, explosive mixtures,smoke, or fire.
46- 46 Reverse-phase or phase-balance
current relay is a relay that functions when the polyphasecurrents are of reverse phase sequence or when the polyphase currents areunbalanced or contain negative phase-sequence
components above a given amount.
47- 47 Phase-sequence or phase-balance
voltage relay functions upon a predetermined value ofpolyphase voltage in the desired phase sequence, or when the polyphase voltagesare unbalanced, or when the negative phase-sequence voltage exceeds a givenamount.
48- 48 Incomplete sequence relay
is a relay that generally returns the equipment to thenormal, or off, position and locks it out if the normal starting, operating, orstopping sequence is not properly completed within a predetermined time. If thedevice is used for alarm purposes only, it should preferably
be designated as 48A (alarm).
49- 49 Machine or transformer thermal
relay is a relay that functions when the temperature of amachine armature winding or other load-carrying winding or element of a machineor power transformer exceeds a redetermined
value.
50- 50 Instantaneous over current relay
is a relay that functions instantaneously on anexcessive value of current.
51- 51 Ac time over current relay
is a relay with either a definite or inverse timecharacteristic that functions when the ac input current exceeds a predeterminedvalue, and in which the input current and operating time are independentlyrelated or inversely related through a substantial portion of the performancerange.
52- 52 Ac circuit breaker
is a device that is used to close and interrupt an acpower circuit under normal conditions
or to interrupt this circuit under fault or emergencyconditions.
53- 53 Exciter or dc generator relay
is a relay that forces the dc machine field excitationto build up during starting or that functions when the machine voltage hasbuilt up to a given value.
54- 54 Turning gear engaging device
is an electrically operated, controlled, or monitoreddevice that functions to cause the turning gear to engage (or disengage) themachine shaft.
55- 55 Power factor relay
is a relay that operates when the power factor in anac circuit rises above or falls below a
predetermined value.
56- 56 Field application relay
is a relay that automatically controls the applicationof the field excitation to an ac motor at
some predetermined point in the slip cycle.
57- 57 Short-circuiting or grounding device
is a primary circuit switching device that functions toshort circuit or ground a circuit in response to automatic or manual means.
58- 58 Rectification failure relay
is a device that functions if a power recitifier failsto conduct or block properly.
59- 59 Over voltage relay
is a relay that operates when its input voltage ishigher than a predetermined value.
60- 60 Voltage or current balance relay
is a relay that operates on a given difference in voltage,or current input or output,
of two circuits.
61- 61 Density switch or sensor
is a device that operates on a given value, or a givenrate of change, of gas density.
62- 62 Time-delay stopping or opening relay
is a time-delay relay that serves in conjunction with thedevice that initiates the shutdown, stopping, or opening operation in anautomatic sequence or protective relay system.
63- 63 Pressure switch
is a switch that operates on given values, or on agiven rate of change, of pressure.
64- 64 Ground detector relay
is a relay that operates upon failure of machine orother apparatus insulation to ground,
or on flashover of a dc machine to ground.
Note:This function is assigned only to a relay which detects the flow of currentfrom the frame of a machine or enclosing case or structure of a piece ofapparatus to ground, or detects a ground on a normally ungrounded winding orcircuit. It is not applied to a device connected in the secondary neutral of acurrent transformer, or in the secondary neutral of current transformers,connected in the power circuit of a normally grounded system.
65- 65 Governor
is the assembly of fluid, electrical, or mechanicalcontrol equipment used for regulating the flow of water, steam, or other mediato the prime mover for such purposes as starting, holding speed or load, orstopping.
66- 66 Notching or jogging device
Functions to allow only a specified number of operations ofa given device or equipment, or a specified number of successive operationswithin a given time of each other. It is also a device that functions toenergize a circuit periodically or for fractions of specified time intervals,or that is used to permit intermittent acceleration or jogging of a machine atlow speeds for mechanical positioning.
67- 67 Ac directional over current relay
is a relay that functions on a desired value of ac overcurrent flowing in a predetermined
direction.
68- 68 Blocking relay
is a relay that initiates a pilot signal for blockingof tripping on external faults in a transmission line or in other apparatusunder predetermined conditions, or that cooperates
with other devices to block tripping or to block reclosing onan out-of-step condition or on power swings.
69- 69 Permissive control device
is generally, a two-position device that in oneposition permits the closing of a circuit
breaker, or the placing of an equipment into operation, andin the other position prevents the circuit breaker or the equipment from beingoperated.
IEEE device numbers
70- 70 Rheostat
is a variable resistance device used in an electriccircuit which is electrically operated or has other electrical accessories,such as auxiliary, position, or limit switches.
71- 71 Level switch
is a switch that operates on given values, or on agiven rate of change, of level.
72- 72 Dc circuit breaker
is used to close and interrupt a dc power circuitunder normal conditions or to interrupt this
circuit under fault or emergency conditions.
73- 73 Load-resistor contactor
is used to shunt or insert a step of load limiting,shifting, or indicating resistance in a
power circuit, or to switch a space heater in circuit, or toswitch a light, or regenerative load resistor of a power rectifier or othermachine in and out of circuit.
74- 74 Alarm relay
is a relay other than an annunciator, as covered underdevice function 30, that is used to operate, or that operates in connectionwith, a visual or audible alarm.
75- 75 Position changing mechanism
is a mechanism that is used for moving a main devicefrom one position to another in an equipment; for example, shifting a removablecircuit breaker unit to and from the connected, disconnected, and test positions.
76-76 Dc over current relay
is a relay that functions when the current in a dccircuit exceeds a given value.
77- 77 Telemetering device
is a transmitter used to generate and transmit to aremote location an electrical signal
representing a measured quantity, or a receiver used toreceive the electrical signal from a remote transmitter and convert the signalto represent the original measured quantity.
78- 78 Phase-angle measuring or out-of step
protective relay is a relay that functions at a predeterminedphase angle between two voltages, or between two currents, or between voltageand current.
79- 79 Ac reclosing relay
is a relay that controls the automatic reclosing andlocking out of an ac circuit interrupter.
80- 80 Flow switch
is a switch that operates on given values, or on a givenrate of change, of flow.
81- 81 Frequency relay
is a relay that responds to the frequency of anelectrical quantity, operating when
the frequency or rate of change of frequency exceeds or isless than a predetermined value.
82 82 Dc load-measuring reclosing relay
is a relay that controls the automatic closing and reclosingof a dc circuit interrupter, generally in response to load circuit conditions.
83- 83 Automatic selective control or transferrelay
is a relay that operates to select automaticallybetween certain sources or conditions in an
equipment or that performs a transfer operationautomatically.
84- 84 Operating mechanism
is the complete electrical mechanism orservomechanism, including the operating
motor, solenoids, position switches, etc., for a tapchanger, induction regulator,
or any similar piece of apparatus that otherwise has nodevice function number.
85 Carrier or pilot-wire receiver relay
Is a relay that is operated or restrained by a signalused in connection with carrier-current or dc pilot-wire fault directionalrelaying.
86- 86 Lockout relay
is an electrically operated hand or electrically resetauxiliary relay that is operated upon
the occurrence of abnormal conditions to maintain associatedequipment or devices out of service until it is reset.
87- 87 Differential protective relay
is a protective relay that functions on a percentage, orphase angle, or other quantitative difference between two currents or someother electrical quantities.
88- 88 Auxiliary motor or motor generator
is a device used for operating auxiliary equipment, such aspumps, blowers, exciters, rotating magnetic amplifiers, etc.
89- 89 Line switch
is used as a disconnecting, load interrupter, orisolating switch in an ac or dc power circuit. (Thisdevice function number isnormally not necessary unless the switch is electrically operated or haselectrical accessories, such as an auxiliary switch, a magnetic lock, etc.)
90- 90 Regulating device
functions to regulate a quantity or quantities, such asvoltage, current, power, speed,
frequency, temperature, and load, at a certain value orbetween certain (generally close) limits for machines, tie lines, or otherapparatus.
91- 91 Voltage directional relay
is a relay that operates when the voltage across an opencircuit breaker or contactor
exceeds a given value in a given direction.
92- 92 Voltage and power directional relay
is a relay that permits or causes the connection of twocircuits when the voltage difference between them exceeds a given value in apredetermined direction and causes these two
circuits to be disconnected from each other when the powerflowing between them exceeds a given value in the opposite direction.
93- 93 Field-changing contactor
Functions to increase or decrease, in one step, the value offield excitation on a machine.
94- 94 Tripping or trip-free relay
Functions to trip a circuit breaker, contactor, orequipment, or to permit immediate
tripping by other devices; or to prevent immediate reclosingof a circuit interrupter
if it should open automatically, even though its closingcircuit is maintained closed.
95- 95
96- 96
97- 97
98- 98
99- 99
Used only for specific applications on individualinstallations where none of the assigned numbered functions from 1 to 94 issuitable.
IEEE device numbers
Supervisory control and indication.
A similar series of numbers, prefixed by the letters RE (for“remote”) shall be used for the interposing relays performing functions thatare controlled directly from the supervisory
system. Typical examples of such device functions are: RE1,RE5 and RE94.
Note:The user of the “RE” prefix for this purpose in place of the former 200 seriesof numbers now makes it possible to obtain increased flexibility of the devicefunction numbering system. For example, in pipeline pump stations, the numbers1 through 99
are applied to device functions that are associated with theover-all station
operation. A similar series of numbers,
starting with 101 instead of 1, are used for those devicefunctions that are associated with unit 1; a similar series starting with 201for device functions that are associated with unit
2; and so on, for each unit in these installations.
Devices performing more than one function
If one device performs two relatively important functions inan equipment so that it is
desirable to identify both of these functions, this may bedone by using a double function
number and name such as:
50/51 Instantaneous and Time Over current
relay.
Suffix numbers
If two or more devices with the same function number andsuffix letter (if used) are present
in the same equipment, they may be distinguished by numberedsuffixes as for example,
52X-1, 52X-2 and 52X-3, when necessary.
Suffix letters
Suffix letters are used with device function numbers forvarious purposes. In order to prevent
possible conflict each suffix letter should have only onemeaning in an individual equipment. All other words should use theabbreviations as contained in American Standard Z32.13-1950, or latest revisionthereof, or should use some other distinctive abbreviation, or be written outin full each time they are used.
The meaning of each single suffix letter, or combination ofletters, should be clearly designated in the legend on the drawings orpublications applying to the equipment. In cases where the same suffix(consisting of one letter or a combination of letters) has different meaningsin the same equipment, depending upon the device function number with which isused, then the complete device function number with which it is used, thecomplete device function number with its suffix letter or letters and itscorresponding function name should be listed in the legend in each case, asfollows: 90V, Voltage regulator. Lower case (small) suffix letters are used inpractically all instances on electrical diagrams for the auxiliary, position,and limit switches. Capital letters are generally used for all other suffixletters.
The letters should generally form part of the devicefunction designation, are usually written
directly after the device function number, as for example,52CS, 71W, or 49D. When it
is necessary to use two types of suffix letters inconnection with one function number, it is
often desirable for clarity to separate them by a slantedline or dash, as for example,
20D/CS or 20D-CS. The suffix letters which denote parts ofthe main device, and those which cannot or need not form part of the devicefunction designation, are generally written directly below the device functionnumber on drawings, as for example, or .
52/CC or 43/A
Auxiliary devices Separate auxiliary devicesActuating quantities
These letters indicate the condition or electrical quantityto which the device responds, or the medium in which it is located, such as:
Main devices
These letters denote the location of the main device in thecircuit, or the type of circuit in
which the device is used or the type of circuit or apparatuswith which it is associated, when
this is necessary, such as:
X
Y –Auxiliary relay 1)
Z
R– Raising relay
L– Lowering relay
O– Opening relay or contactor
C –Closing relay or contactor
CS– Control switch
CL– Auxiliary relay, open (energized when main device is in open position)
OP– Auxiliary relay, open (energized when main device is in open position)
U– “Up” position-switch relay
D– “Down” position-switch relay
PB –Push button
1) In the control of a circuit breaker with so-called
X-Yrelay control scheme, the X relay is the device whose main contacts are used toenergize
the closing coil or the device which in some other manner,such as by the release of stored energy, causes the breaker to close.
The contacts of the Y relay provide the antipump feature forthe circuit breaker.
A– Air or Amperes or Alternating
C– Current
D– Direct or Discharge
E– Electrolyte
F– Frequency, or Flow, or Fault
H– Explosive
J –Differential
L– Level, or Liquid
P –Power, or Pressure
PF– Power factor
Q– Oil
S– Speed, or Suction, or Smoke
T –Temperature
V– Voltage, Volts, or Vacuum
VAR– Reactive power
VB– Vibration
W– Water, or Watts
A– Alarm or Auxiliary power
AN– Anode
B– Battery, or Blower, or Bus
BK –Brake
BL– Block (Valve)
BP– Bypass
BT –Bus tie
C– Capacitor, or Condenser, or Compensator, or Carrier current, or Case, orCompressor
CA– Cathode
CH– Check (Valve)
D– Discharge (Valve)
E –Exciter
F– Feeder, or Field, or Filament, or Filter, or Fan
G– Generator, or Ground2)
H –Heater, or Housing
L –Line, or Logic
M– Motor, or Metering
N– Network, or Neutral 2)
P– Pump, or Phase comparison
R– Reactor, or Rectifier, or Room
S– Synchronizing, or Secondary, or
Strainer, or Sump, or Suction (Valve)
T– Transformer, or Thyratron
TH– Transformer (high-voltage side)
TL– Transformer (low-voltage side)
TM– Telemeter
U– Unit
2) Suffix “N” is generally used in preference to “G” fordevices connected in the secondary neutral of current transformers, or in thesecondary of a current transformer whose primary winding is located in theneutral of a machine or power transformer, except in the case of transmissionline relaying, where the suffix “G” is more commonly used for those relayswhich operate on ground faults.
Main device parts
These letters denote parts of the main device, divided inthe two following categories:
1. All parts, except auxiliary contacts, positionswitches, limit switches, and torque limit
switches.
2. All auxiliary contacts and positioning andlimit switches
for such devices and equipment as circuit breakers,contactors, valves and rheostats
and contacts of relays. These are designated as follows:
Standard reference positions of some typicaldevices are as follows:
BK – Brake
C – Coil, or Condenser, or Capacitor
CC – Closing coil
HC – Holding coil
M – Operating motor
MF – Fly-ball motor
ML – Load-limit motor
MS – Speed adjusting, or Synchronizing
motor
S – Solenoid
SI – Seal-in
TC – Trip coil
V – Valve
a – Contact that is open when the main device is in the standardreference position, commonly referred to as the nonoperated or reenergizedposition and that closes when the device assumes the opposite position.
b – Contact that is closed when the main device is in thestandard reference position, commonly referred to as the nonoperated ordeenergized position, and that opens when the device assumes the oppositeposition.
aa – Contact that is open when the operating mechanism ofthe main device is in the
nonoperated position and that closes when the operating mechanismassumes the opposite position.
bb – Contact that is closed when the operating mechanism ofthe main device is in
the nonoperated position and that opens when the operatingmechanism assumes the opposite position.
Device Standard reference position
Power circuit breaker Main contacts open
Disconnecting switch Main contacts open
Load-break switch Main contacts open
Valve Closed position
Gate Closed position
Clutch Disengaged position
Turning gear Disengaged position
Power electrodes Maximum gap position
Rheostat Maximum resistance
position
Adjusting means 1) Low or Down position
Relay 2) Deenergized position
Contactor 2) Deenergized position
Relay (latched-in type)
Non-latched-in position
Contactor (latched-in type)
Main contacts open
Temperature relay 3) Lowest temperature
Level detector 3) Lowest level
Flow detector 3) Lowest flow
Speed switch 3) Lowest speed
Vibration detector 3) Minimum vibration
Pressure switch 3) Lowest pressure
Vacuum switch 3) Lowest pressure, i.e.,
highest vacuum
The simple designation “a” or “b” is used in all cases wherethere is no need to adjust the
contacts to change position at any particular point in thetravel of the main device or where the part of the travel where the contactschange position is of no significance in the control or operating scheme. Hencethe “a” and “b” designations usually are sufficient for circuit breakerauxiliary switches.
Note: If several similar auxiliary switches are present onthe same device, they should be designated numerically 1, 2, 3, etc. whennecessary.
Other switches
These letters cover all other distinguishing
features or characteristics or conditions,
which serve to describe the use of the device
or its contacts in the equipment such as:
Device Standard reference position
1) These may be speed, voltage, current, load, or similaradjusting devices comprising rheostats, springs, levers, or other componentsfor the purpose.
2) These electrically operated devices are of thenon-latched-in type, whose contact position is dependent only upon the degreeof energization of the operating or restraining or holding
coil or coils which may or may not be suitable forcontinuous energization. The deenergized
position of the device is that with all coils deenergized.
3) The energizing influences for these devices areconsidered to be, respectively, rising
temperature, rising level, increasing flow, rising speed,increasing vibration, and increasing
pressure.
A – Accelerating, or Automatic
B – Blocking, or Back-up
C – Close, or Cold
D – Decelerating, or Detonate, or Down, or
Disengaged
E – Emergency, or Engaged
F – Failure, or Forward
H – Hot, or High
HR – Hand reset
HS – High speed
L – Left, or Local, or Low, or Lower, or
Leading
M – Manual
OFF – Off
ON – On
P – Polarizing
R – Right, or Raise, or Reclosing, or Receiving, or Remote,or Reverse
S – Sending, or Swing
T – Test, or Trip, or Trailing
TDC – Time-delay closing
TDO – Time-delay opening
موضوع: Basic of protection system *****part 3 
