2. I n t e r i o r communication switchboards and
Maintenance
panels
If any problems are discovered during the testing of
3. ECSS consoles
bus transfer equipment, you, as the GSE, must correct
4. Steering power panels
them immediately. Remember to follow all standard
electrical safety precautions when you are
Manual bus transfer (MBT) units are used for all
troubleshooting and repairing bus transfer equipment.
loads having low voltage protection (LVP) control
features, except in the case of pumps associated with the
Your first step in the maintenance of bus transfer
main and auxiliary machinery plant which have their
equipment is to perform a functional check of the ABT
own low voltage release (LVR) control features. MBT
or MBT. You will normally follow the applicable PMS
units are also used for loads having manual restart after
card to perform this check. Your check should include
a voltage failure and for electronics power distribution
cycling or shifting the bus transfer equipment from the
panels. Loads that have LVR or LVP control features and
normal to the alternate power source and vice versa.
require two sources of supply are sometimes combined
Observe the operation and note any problems that occur.
and supplied from an ABT unit. MBT units are located
as close as possible to the panel or equipment being fed
U s e the correct procedures for performing a
from the bus transfer unit.
functional check of an MBT by taking the following
steps:
On power systems, there is a short time delay after
the normal feeder is de-energized and before the ABT
1. Make certain the alternate power indicator lamp
switch takes over. During this shift, the load is without
is on, showing that alternate power is available.
power. Remember, however, that ABT switches on
2. Open the normal power circuit breaker (CB).
lighting systems have no time delay and transfer power
instantaneously.
3. Shift the interlock to prevent closure of the
normal power CB, and enable the closure of the alternate
Testing
power CB.
4. Close the alternate power CB.
Bus transfer equipment should be tested according
Using these steps, you will shift the MBT back to
to your ship's preventive maintenance system (PMS)
the normal power source. The MBT shifting process is
schedule. For MBT equipment, manually transfer a load
purely a mechanical one. If power is not transferred
from one power source to another. Check the
mechanical operation and mechanical interlocks of the
during the functional check, look for a faulty CB in the
MBT. For ABT equipment, check the operation by using
MBT unit.
the test switches. Your test should include a check to see
You can perform the functional check of an ABT in
if operation starts after you cut off power (by opening
two ways. First, manually test the ABT by placing the
the feeder circuit breaker). This check will confirm that
control disconnect switch in the MANUAL position and
the automatic transfer unit is working.
shifting the manual switch to the opposite position. (See
fig. 5-22.) Second, automatically test the ABT by
placing the control disconnect switch in the AUTO
CAUTION
position and turning the spring-loaded test switch to the
When you are testing the ABT units, be careful they
TEST position. The ABT should shift to the alternate
do not supply vital and sensitive electronic circuitry.
power source. Releasing the spring-loaded test switch
Some sensitive electronic circuits are adversely affected
allows the ABT to shift back to the normal source of
by a loss and almost instant return of power. Before
power. If the ABT fails to perform in this reamer, you
c o n d u c t i n g the test, make certain all personnel
must begin troubleshooting.
concerned are informed of the power interruptions.
Various types of ABTs are used throughout the
Be careful when testing an MBT unit. Make certain
Navy. You must make certain you get the correct
you follow the correct procedure when shifting an MBT
manufacturer's technical manual before you begin to
f r o m normal to alternate power. You should get
troubleshoot and repair the ABT. Once again, follow all
permission from the EOOW before starting the test of
standard electrical safety precautions when working on
an MBT. Failure to do so could cause loss of vital
equipment that is on line.
this equipment.
5-22
