IEEE device numbers and functions for switchgear apparatus


 The devices in switching equipments are referred to by numbers, with appropriate suffix

letters when necessary, according to the functions they perform. These numbers are based on a system adopted as standard for automatic switchgear by IEEE, and incorporated in American

Standard C37.2-1979. This system is used in connection diagrams, in instruction books,

and in specifications.



Device Number  Definition and function


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



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



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



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.