The emergency/alternate switchboard is energized
The emergency or alternate system consists of
through either the bus tie circuit breaker from the ships
selected groups of fixtures that are fed through
service switchboard or its attached emergency/alternate
automatic bus transfer (ABT) equipment. Atypical vital
generator through a generator circuit breaker. Transfer
lighting load is supplied from two separate switchboards
(fig. 4-1). Normally the power is supplied from the ship
between these supplies is accomplished automatically
by three electrical y operated circuit breakers. The
service distribution system but, upon loss of power, is
circuit breakers are electrical y and mechanical] y
shifted by the ABT to the emergency or alternate source
interlocked to prevent the closing of more than one
to keep vital lighting loads energized
breaker at a time.
If an undervoltage condition occurs while the ships
OPERATION
service generator(s) is/are supplying the load with an
output frequency of 57 Hz or higher, the following
Under normal conditions, the system shown in
conditions will occur:
figure 4-2 operates as follows:
circuitry in the switchboard will operate to open
1. Power is supplied from the ship service
the bus tie circuit breakers in the emergency or
distribution switchboard.
alternate switchboard
2. If an undervoltage condition develops on the
the emergency or alternate generator will be
ship service switchboard which is the normal
started
supply for the ABT, the ABT switch will transfer
when the emergency or alternate generator is up
the emergency lighting load to the alternate
source of power.
to speed and producing 450 VAC, the generator
Figure 4-1.--Lighting distribution system.
4-2
