UFC 3 -520-01
June 10, 2002
PROTECTIVE DEVICE DESIGNATIONS.
Every protective device has an associated device function number. These
numbers are designated by ANSI/IEEE C37.2, IEEE Standard Electrical Power System
Device Function Numbers
. The numbering scheme defined
by this national standard
used in electrical schematics, engineering specifications, textbooks, and other
documents referring to electrical devices. The designations most likely to be used in
interior electrical facilities are provided in Table 9 -2. Refer to ANS I/IEEE C37.2 for a
complete list of protective device designations. Use these designations as applicable
on all electrical drawings.
Table 9-2. Protective Device Designations
Definition and Function
Master Element is the initiating device, such as a control switch, voltage
relay, or float switch, which serves either directly, or through such
permissive devices as protective and time -delay relays to place an
equipment in or out of operation.
Time-Delay Starting, or Closing, Re lay is a device that functions to give a
desired amount of time delay before or after any point or operation in a
switching sequence or protective relay system, except as specifically
provided by device numbers 62 or 79 described later.
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.
Master Contactor is a device, generally controlled by device number 1 or
equivalent, and the necessary permissive and protective devices, which
serves to make and break the necessary control circuits to p lace an
equipment into operation under the desired conditions and to take it out of
operation under other or abnormal conditions.
Stopping Device functions to place and hold an equipment out of operation.
Starting Circuit Breaker is a device whose principal function is to connect a
machine to its source of starting voltage.
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
connecting and disconnec ting, respectively, 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