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6.3.1.2 Live-Front. Live-front switchboards have the circuit breakers and switches
mounted directly on the front of the panels and are generally limited to 250 VDC and 600 VAC.
These are seldom used in modern designs.
6.3.1.3 Dead-Front. Dead-front switchboards have the breakers and switches mounted on
the rear of the panels and are generally limited to a maximum of 600 VDC and 2,500 VAC. All
designs are operated from the front, providing safety to the operator. Some types are also
equipped with interlocking features that prevent access to live parts.
6.3.1.4 Control-Power. Control-power switchboards are used in generating stations and
substations to provide a separate source of energy for the control of electrically operated
apparatus. The voltages ordinarily used are 125 and 250 VDC. The switchboards generally
include control for a storage battery, one or two motor-generators, and the required number of
feeder panels.
6.3.1.5 Medium-Voltage. Medium-voltage metal-clad switchboards for 15,000 V or less,
consist of equipment housed in steel compartments completely assembled by the manufacturer.
This type of switchboard design is generally used for light, power, and station auxiliary power
supply in large generating stations and industrial plants. It is also used extensively for AC
substation switching. As all medium-voltage parts are enclosed, the equipment is interlocked to
prevent mistakes in operation. All parts of the steel enclosure are grounded providing maximum
safety to the operator for this class of switchboard. The secondary wiring is shielded, and
barriers are provided between phases and between adjacent circuit breakers.
6.3.1.6 Electrically Operated. Electrically operated switchboards employ solenoid- or
motor-operated mechanisms, some with stored-energy-type designs for circuit breaker operation.
These are, in general, controlled from a central point or control board. This arrangement allows
for the location of the control board to be independent of the location of the power board.
Complete isolation of the high-tension equipment has been made possible.
6.3.2 Control Boards. The control of large power circuits by electrically operated breakers
has effected the replacement of the switchboard by the control board. Several types of control
boards are in general use. On these are mounted the necessary control switches, lights to
indicate the positions of the breakers, indicating and recording instruments, and relays. The
arrangements of devices on the boards are simple and distinctive to aid the operator in avoiding
confusion and mistakes under normal and emergency conditions. The control and indicating
devices of each main power circuit are clearly set off from those of other circuits. The
assembly of the panels and the selection of the type of panel depend entirely upon the size and
type of station and on local conditions.
6.3.2.1 Indicating Lamps. Indicating lamps are used to indicate breaker position; green
lights indicating open breakers and red lights indicating closed breakers. White lights are
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