NEMA CODE

2	Time delay relay
3	Checking or Interlocking relay
21	Distance relay
25	Check synchronizing relay
27	Undervoltage relay
30	Annunciator relay
32	Directional power (Reverse power) relay
37	Low forward power relay
40	Field failure (loss of excitation) relay
46	Negative phase sequence relay
49	Machine or Transformer Thermal relay
50	Instantaneous Overcurrent relay
51	A.C IDMT Overcurrent relay
52	Circuit breaker
52a	Circuit breaker Auxiliary switch “Normally open” (‘a’ contact)
52b	Circuit breaker Auxiliary switch “Normally closed” (‘b’ contact)
55	Power Factor relay
56	Field Application relay
59	Overvoltage relay
60	Voltage or current balance relay
64		Earth fault relay
67		Directional relay
68		Locking relay
74		Alarm relay
76		D.C Overcurrent relay
78		Phase angle measuring or out of step relay
79		AC Auto reclose relay
80		Monitoring loss of DC supply
81		Frequency relay
81U		Under frequency relay
81O		Over frequency relay
83		Automatic selective control or transfer relay
85		Carrier or pilot wire receive relay
86		Tripping Relay
87		Differential relay
87G		Generator differential relay
87GT		Overall differential relay
87U		UAT differential relay
87NT		Restricted earth fault relay
95		Trip circuit supervision relay
99		Overflux relay
186A		Auto reclose lockout relay
186B		Auto reclose lockout relay

1- 1 Master element 

is the initiating device, such as a control switch, voltage relay, float switch etc., that serves either irectly, or through such permissive devices as protective and 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 time delay before or after any point of operation in a switching sequence or protective relay 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 other devices, (or to a number of predetermined conditions), in an equipment to allow an operating sequence to proceed,

to stop, or to provide a check of the position of these devices or of these conditions for any purpose.

4- 4 Master contactor

is a device, generally controlled by device No. 1 or equivalent, and the required permissive

and protective devices, that serve to make and break the necessary control circuits to place an equipment into operation under the desired 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 equipment and hold it out of operation. [This device may be manually or electrically actuated, but excludes the function of

electrical lockout (see device function 86) on abnormal conditions.]

6- 6 Starting circuit breaker

 is a device whose principal function is to connect a machine to its source of starting

voltage.

7- 7 Rate-of-rise relay

 is a relay that functions on an excessive rate of rise of 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 respectively connecting and disconnecting the source of control power to and from the control bus or equipment.

9- 9 Reversing device

 is used for the purpose of reversing a machine field or for performing any other reversing

functions.

10- 10 Unit sequence switch

 is used to change the sequence in which units may be placed in and out of service in

multiple-unit equipment.

11- 11 Multifunction device

 is a device that performs three or more comparatively important functions that could only be

designated by combining several of these device function numbers. All of the functions performed by device 11 shall be defined in the drawing legend or device function list.

12- 12 Over speed device

 is usually a direct connected speed switch that functions on machine over speed.

13- 13 Synchronous-speed device

 such as a centrifugal speed switch, a slip frequency relay, a voltage relay, an undercurrent relay, or any other type of device that operates at approximately the synchronous speed of a

machine.

14- 14 Under speed device

 functions when the speed of a machine falls below a pre-determined value.

15- 15 Speed or frequency matching device

functions to match and hold the speed or the frequency of a machine or of a system equal to, or approximately equal to, that of another machine, 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 any piece 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 shunting operations as may be necessary in the process of starting a machine by devices 6 or 42, or their equivalent, and also excludes

device 73 function that serves for the switching of resistors.

 18- 18 Accelerating or decelerating device

 is used to close or to cause the closing of circuits that 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 the automatic transfer of a machine from the starting to the running power connection.

20- 20 Electrically operated valve

 is an electrically operated, controlled, or monitored valve used in a fluid, air, gas, or vacuum line.

Note: The function of the valve may be indicated by the use of 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 and break the equalizer or the current balancing

connections for a machine field, or for regulating equipment, in a multiple unit installation.

23- 23 Temperature control device

 Functions to raise or to lower the temperature of a machine or other apparatus, or of any medium, when its temperature falls below or rises above a predetermined value.

Note: An example is a thermostat that switches on a space heater in a switchgear assembly when the temperature falls to a desired value as distinguished from a device that is used to provide automatic temperature regulation 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 to frequency exceeds a preset value.

The relay may have an instantaneous or a time characteristic.

25- 25 Synchronizing or synchronism check

device operates when two ac circuits are within the desired limits of frequency, phase angle, or voltage to permit or to cause the paralleling of these two circuits.

26- 26 Apparatus thermal device

 Functions when the temperature of the protected apparatus (other than the loadcarrying

windings of machines and transformers as covered by device function number 49) or of a liquid or other medium exceeds a predetermined value; or when the temperature of the protected apparatus or of any medium decreases below a predetermined value.

27- 27 Under voltage relay

is a relay that  operates when its input voltage is less than a predetermined value.

28- 28 Flame detector

 is a device that monitors the presence of the pilot or main flame in such apparatus as a gas

turbine or a steam boiler.

29- 29 Isolating contactor

 is used expressly for disconnecting one circuit from another for the purposes of emergency

operation, maintenance, or test.

30 Annunciator relay

 is a nonautomatically reset device that gives a number of separate visual indications upon the functioning of protective devices and that 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 synchronous converter, to a source of separate excitation during the starting sequence; or one 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 of power flow in a given direction or upon reverse power flow such as that resulting 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 piece of 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 contact switch, or the equivalent, or a programming device, such as a computer, that establishes or determines the

operating sequence of the major devices in an equipment during starting

and stopping or during other sequential switching operations.

35- 35 Brush-operating or slip-ring short circuiting

device is used for raising, lowering or shifting the brushes of a machine; short-circuiting its slip rings; or engaging or disengaging the contacts of a mechanical rectifier.

36- 36 Polarity or polarizing voltage device

operates, or permits the operation of, another device on a predetermined polarity only or that

verifies the presence of a polarizing voltage in an equipment.

37- 37 Undercurrent or under power relay

functions when the current or power flow decreases below a predetermined value.

38- 38 Bearing protective device

 Functions on excessive bearing temperature or on other abnormal mechanical conditions

associated with the bearing, such as undue wear, which may eventually result in excessive bearing temperature or failure.

 39- 39 Mechanical condition monitor

 is a device that functions upon the occurrence of an abnormal mechanical condition (except that associated with bearings as covered under 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 or failure of machine field current, or on an excessive value of the reactive component of armature current in an ac machine indicating abnormally low field excitation.

41- 41 Field circuit breaker

is a device that functions to apply or remove the field excitation of a machine.

42- 42 Running circuit breaker

 is a device whose principal function is to connect a machine to its source of running or

operating voltage. This function may also be used for a device, such as a contactor, that is used in series with a circuit breaker or other fault protecting means, primarily for frequent opening and closing of the circuit.

43- 43 Manual transfer or selector device

is a manually operated device that transfers the control circuits in order to modify the plan of operation of the switching equipment or of some of the devices.

44- 44 Unit sequence starting relay

 is a relay that functions to start the next available unit in multiple unit equipment upon the failure or nonavailability of the normally preceding unit.

45- 45 Atmospheric condition monitor

 is a device that functions upon the occurrence of an abnormal 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 polyphase currents are of reverse phase sequence or when the polyphase currents are unbalanced or contain negative phase-sequence

components above a given amount.

47- 47 Phase-sequence or phase-balance

voltage relay functions upon a predetermined value of polyphase voltage in the desired phase sequence, or when the polyphase voltages are unbalanced, or when the negative phase-sequence voltage exceeds a given amount.

48- 48 Incomplete sequence relay

is a relay that generally returns the equipment to the normal, or off, position and locks it out if the normal starting, operating, or stopping sequence is not properly completed within a predetermined time. If the device 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 a machine armature winding or other load-carrying winding or element of a machine or power transformer exceeds a redetermined

value.

50- 50 Instantaneous over current relay

 is a relay that functions instantaneously on an excessive value of current.

51- 51 Ac time over current relay

 is a relay with either a definite or inverse time characteristic that functions when the ac input current exceeds a predetermined value, and in which the input current and operating time are independently related or inversely related through a substantial portion of the performance range.

52- 52 Ac circuit breaker

 is a device that is used to close and interrupt an ac power circuit under normal conditions

or to interrupt this circuit under fault or emergency conditions.

53- 53 Exciter or dc generator relay

 is a relay that forces the dc machine field excitation to build up during starting or that functions when the machine voltage has built up to a given value.

54- 54 Turning gear engaging device

 is an electrically operated, controlled, or monitored device that functions to cause the turning gear to engage (or disengage) the machine shaft.

55- 55 Power factor relay

 is a relay that operates when the power factor in an ac circuit rises above or falls below a

predetermined value.

56- 56 Field application relay

 is a relay that automatically controls the application of 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 to short 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 fails to conduct or block properly.

59- 59 Over voltage relay

 is a relay that operates when its input voltage is higher 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 given rate of change, of gas density.

62- 62 Time-delay stopping or opening relay     

is a time-delay relay that serves in conjunction with the device that initiates the shutdown, stopping, or opening operation in an automatic sequence or protective relay system.

63- 63 Pressure switch

 is a switch that operates on given values, or on a given rate of change, of pressure.

64- 64 Ground detector relay

 is a relay that operates upon failure of machine or other 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 current from the frame of a machine or enclosing case or structure of a piece of apparatus to ground, or detects a ground on a normally ungrounded winding or circuit. It is not applied to a device connected in the secondary neutral of a current 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 mechanical control equipment used for regulating the flow of water, steam, or other media to the prime mover for such purposes as starting, holding speed or load, or stopping.

66- 66 Notching or jogging device

Functions to allow only a specified number of operations of a given device or equipment, or a specified number of successive operations within a given time of each other. It is also a device that functions to energize a circuit periodically or for fractions of specified time intervals, or that is used to permit intermittent acceleration or jogging of a machine at low speeds for mechanical positioning.

67- 67 Ac directional over current relay

is a relay that functions on a desired value of ac over current flowing in a predetermined

direction.

68- 68 Blocking relay

 is a relay that initiates a pilot signal for blocking of tripping on external faults in a transmission line or in other apparatus under predetermined conditions, or that cooperates

with other devices to block tripping or to block reclosing on an out-of-step condition or on power swings.

69- 69 Permissive control device

 is generally, a two-position device that in one position permits the closing of a circuit

breaker, or the placing of an equipment into operation, and in the other position prevents the circuit breaker or the equipment from being operated.

70- 70 Rheostat  

 is a variable resistance device used in an electric circuit 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 a given rate of change, of level.

72- 72 Dc circuit breaker

 is used to close and interrupt a dc power circuit under 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 to switch a light, or regenerative load resistor of a power rectifier or other machine in and out of circuit.

74- 74 Alarm relay

 is a relay other than an annunciator, as covered under device function 30, that is used to operate, or that operates in connection with, a visual or audible alarm.

75- 75 Position changing mechanism

 is a mechanism that is used for moving a main device from one position to another in an equipment; for example, shifting a removable circuit 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 dc circuit exceeds a given value.

77- 77 Telemetering device

 is a transmitter used to generate and transmit to a remote location an electrical signal

representing a measured quantity, or a receiver used to receive the electrical signal from a remote transmitter and convert the signal to represent the original measured quantity.

78- 78 Phase-angle measuring or out-of step

protective relay is a relay that functions at a predetermined phase angle between two voltages, or between two currents, or between voltage and current.

79- 79 Ac reclosing relay

 is a relay that controls the automatic reclosing and locking out of an ac circuit interrupter.

80- 80 Flow switch

is a switch that operates on given values, or on a given rate of change, of flow.

81- 81 Frequency relay

 is a relay that responds to the frequency of an electrical quantity, operating when

the frequency or rate of change of frequency exceeds or is less than a predetermined value.

82- 82 Dc load-measuring reclosing relay

is a relay that controls the automatic closing and reclosing of a dc circuit interrupter, generally in response to load circuit conditions.

83- 83 Automatic selective control or transfer relay

 is a relay that operates to select automatically between certain sources or conditions in an

equipment or that performs a transfer operation automatically.

84- 84 Operating mechanism

 is the complete electrical mechanism or servomechanism, including the operating

motor, solenoids, position switches, etc., for a tap changer, induction regulator,

or any similar piece of apparatus that otherwise has no device function number.

85 Carrier or pilot-wire receiver relay

 Is a relay that is operated or restrained by a signal used in connection with carrier-current or dc pilot-wire fault directional relaying.

86- 86 Lockout relay

 is an electrically operated hand or electrically reset auxiliary relay that is operated upon

the occurrence of abnormal conditions to maintain associated equipment or devices out of service until it is reset.

87- 87 Differential protective relay

is a protective relay that functions on a percentage, or phase angle, or other quantitative difference between two currents or some other electrical quantities.

88- 88 Auxiliary motor or motor generator

is a device used for operating auxiliary equipment, such as pumps, blowers, exciters, rotating magnetic amplifiers, etc.

89- 89 Line switch

 is used as a disconnecting, load interrupter, or isolating switch in an ac or dc power circuit. (Thisdevice function number is normally not necessary unless the switch is electrically operated or has electrical accessories, such as an auxiliary switch, a magnetic lock, etc.)

90- 90 Regulating device

functions to regulate a quantity or quantities, such as voltage, current, power, speed,

frequency, temperature, and load, at a certain value or between certain (generally close) limits for machines, tie lines, or other apparatus.

91- 91 Voltage directional relay

is a relay that operates when the voltage across an open circuit 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 two circuits when the voltage difference between them exceeds a given value in a predetermined direction and causes these two

circuits to be disconnected from each other when the power flowing 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 of field excitation on a machine.

94- 94 Tripping or trip-free relay

Functions to trip a circuit breaker, contactor, or equipment, or to permit immediate

tripping by other devices; or to prevent immediate reclosing of a circuit interrupter

if it should open automatically, even though its closing circuit is maintained closed.

95- 95

96- 96

97- 97

98- 98

99- 99

Used only for specific applications on individual installations where none of the assigned numbered functions from 1 to 94 is suitable.

Over Current trip        }

E/f. Trip                       } Relay trip : K3 Master trip

Diffl.Trip                     }

OSR/OLTC trip          :           163T

Bucholz trip                :           63T

O.T trip                       :           26T

W.T trip                       :           49T

Over fluxing trip         :           99

P.R.V trip                    :

Ter.Ala Trip                 :           149T

Bucholz Alarm            :           63A

W.T Alarm                  :           49A

O.T Alarm                   :           26A

Ter.Alarm                    :           149A

Busbar prot. Trip         :           96

Pole discrepancy trip   :           162