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Device function numbers as per IEEE Std C37.2

Device Function Numbers
Standard Title
1 master element A device, such as a control switch, etc., that serves, either directly or through such permissive devices as protective and time-delay relays, to place equipment in or out of operation.
This number is normally used for a hand-operated device, although it may also be used for an electrical or mechanical device for which no other function number is suitable.
2 time-delay starting or closing relay 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, 79, and 82.
3 checking or interlocking relay A device that operates in response to the position of one or more other devices or predetermined conditions in a piece of equipment or circuit, to allow an operating sequence to proceed, or to stop, or to provide a check of the position of these devices or conditions for any purpose.
4 master contactor A device, generally controlled by device function l or the equivalent and the required permissive and protective devices, that serves to make and break the necessary control circuits to place equipment into operation under the desired conditions and to take it out of operation under abnormal conditions.
5 stopping device A control device used primarily to shut down equipment and hold it out of operation. This device may be manually or electrically actuated, but it excludes the function of electrical lockout [see device function 86] on abnormal conditions.
6 starting circuit breaker A device whose principal function is to connect a machine to its source of starting voltage.
7 rate-of-change relay A device that operates when the rate-of-change of the measured quantity exceeds a threshold value, except as defined by device 63.
8 control power disconnecting device A device, such as a knife switch, circuit breaker, or pull-out fuse block, used for the purpose of connecting and disconnecting the source of control power to and from the control bus or equipment.
Control power is considered to include auxiliary power that supplies such apparatus as small motors and heaters.
9 reversing device A device that is used for the purpose of reversing a machine field or for performing any other reversing function.
10 unit sequence switch A device that is used to change the sequence in which units may be placed in and out of service in multiple-unit equipment.
11 multifunction device A device that performs three or more comparatively important functions that could only be designated by combining several device function numbers. All of the functions performed by device 11 shall be defined in the drawing legend, device function definition list or relay setting record. See Annex B for further discussion and examples.
If only two relatively important functions are performed by the device, it is preferred that both function numbers be used, as described in 3.6.
12 overspeed device A device, usually direct connected, that operates on machine overspeed.
13 synchronous-speed device A 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 underspeed device A device that functions when the speed of a machine falls below a predetermined value.
15 speed or frequency matching device A device that functions to match and hold the speed or frequency of a machine or a system equal to, or approximately equal to, that of another machine, source, or system.
16 not used Reserved for future application.
17 shunting or discharge switch A device that serves to open or 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.
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 function 73 that serves for the switching of resistors.
18 accelerating or decelerating device A device that is used to close or cause the closing of circuits that are used to increase or decrease the speed of a machine.
19 starting-to-running transition contactor A device that operates to initiate or cause the automatic transfer of a machine from the starting to the running power connection.
20 electrically operated valve An electrically operated, controlled, or monitored device used in a fluid, air, gas, or vacuum line.
The function of the valve may be more completely indicated by the use of suffixes as discussed in 3.2.
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