IC switchboard is usually the only one required to be
SYNCHRO OVERLOAD TRANSFORMERS
AND INDICATORS.-- Synchro overload transform-
manned. The IC Electrician on watch is responsible
ers and indicators are used in the ACO section of the
for recording hourly voltage, current, frequency, and
IC switchboard to alert operating personnel of a
ground readings of the various buses associated with
casualty or overload in the associated circuit.
the IC switchboard.
The transformers are wired in series with the
When checking for grounds, the watch stander
should compare the readings being taken with
instruments. Type B and C transformers are used for
previous readings. Unusual deviations should be
60-Hz and 400-Hz circuits, respectfully.
investigated and the cause determined. Low voltage
between any phase and ground, with high voltage
When the angular displacement of the synchro
between the other phases and ground, normally
receiver is in excess of 17 ±3 degrees from the position
indicates a ground on the phase with the low-voltage
of its associated transmitter, the indicator lamp
connected to the transformer will glow. This
displacement may be caused by an open or shorted
The watch stander is also responsible for
rotor circuit, an open or shorted stator circuit, or lack
investigating all blown fuse indications, synchro
of synchronism between transmitter and receiver
overload indications, and bus failure alarms.
caused by excessive bearing friction in the receiver.
When an overload indicator lamp is glowing, the
LOCAL IC SWITCHBOARDS
cause of the malfunction should be investigated
immediately and corrected as soon as possible. The
Local IC switchboards are type II, bulkhead-
switchboard operator can isolate the affected
mounted, front-service, enclosed units. Terminal
instrument from the circuit by operating the associated
boards and an ABT are mounted inside the switch-
ACO switch. If the circuit malfunction cannot be
board. Switches, fuse holders, and lamp holders are
determined, check the transformer setting. The
mounted on the door.
indication may be the result of the overload
The number of local IC switchboards installed on
transformer being set too low.
a ship depends on the type and class of that ship. As
stated earlier, local IC switchboards provide local
control of circuits vital to the operation of a space. The
local IC switchboards that will be discussed in this
Operation of an ACO transfer switch
chapter are (1) engine room, (2) central control station,
normally causes the associated overload
and (3) steering gear room. There may be other local
indicator light to flash. This is due to a
IC switchboards installed aboard ships, depending on
momentary displacement between the
individual ship requirements.
transmitter and receiver. The flash is normal
and shows the system is operating properly.
Engine-room Local IC Switchboard
On some ships, a local IC switchboard is provided
POWER MONITORING INSTRUMENTS.--
in each engine room to energize local IC alarm,
The power monitoring instrumentation consists of
warning, and indicating systems.
are also phase selector switches for the voltmeters and
The engine-room switchboard operates on
the ammeters. These various meters are used to check
120-volt, 60-Hz, single- or 3-phase ac power, There
the voltage, current, and frequency of each input
are two sources of power available: normal and
power bus and the presence of grounds.
emergency. The nearest main IC switchboard provides
the normal power supply, The emergency power
supply comes from a local emergency lighting circuit.
The emergency power supply provides the switch-
board with power if the normal supply is lost. The
When a ship is underway, the main IC switchboard
engine-room switchboard includes supply switches,
should be manned 24 hours a day. On ships where
there are two main IC switchboards, the forward main
an ABT device, and power available indicator lights.