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 sometimes included to be energized from potential transformers to indicate live circuits. Some
stations include orange or another distinctive color to indicate that the circuit has tripped
automatically. Red and green lights are commonly wired so that they are energized through the
tripping coil and circuit of the breaker to supervise the trip circuit. An opening in the trip-coil
circuit is then indicated by a dark lamp.
6.3.2.2 Mimic Bus. Mimic buses are frequently installed on the faces of control boards to
aid operation, showing in miniature the bus and the circuit connections controlled by each control
switch.
6.3.2.3 Auxiliary Circuits. Auxiliary circuits used on switchboards provide the following:
(a) The use of one instrument for several machines or circuits is made possible by the
voltmeter bus and switches on plugs.
(b) Current supply for instruments and relays.
(c) Control power supply for operation of circuit breakers and switches.
(d) Annunciator or alarm circuits.
(e) Potential supply for relays.
(f) Synchronizing circuits.
(g) Test supply.
6.3.2.4 Ground Detector. Ground detectors are desirable on ungrounded systems so that
immediate steps may be taken to clear a ground before a second ground occurs. The occurrence
of a second ground, before the first has been cleared, could create a phase-to-phase short circuit.
6.3.3 Supervisory Control Equipment. Supervisory control equipment is often used to
remotely control a number of devices from a distant location, using a minimum number of
communication channels. The basic approach is to select, at one time, a single operating point
and connect the control for that device to the communication channel to permit remote operation.
Generally, only one device can be controlled at one time.
6.3.3.1 Functions. The functions normally performed by supervisory control include the
following:
(a) Opening and closing circuit breakers and disconnect switches from the master
station.
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