8. Shut down the power plant(s) connected to the
power circuit in the load bank. If the CONTROL
CIRCUIT toggle switch (7, fig. 7-63) is in the dc
load bank, then disconnect all cables.
position, all dc loads are dropped. The
OVER-VOLTAGE RESET toggle switch (5) on the dc
WARNING
panel will not reset the control power control unless the
Always make certain that the power supply to the
input voltage is less than 29 volts.
load bank has been completely shut off (check the
DC-VOLT and AC-VOLT meters for indications)
AC Overvoltage Cutout
before disconnecting the power cables.
If the ac voltage applied to the ac input from the
power plant exceeds 130 volts (phase A to neutral), a
9. Close and secure all covers and doors on the load
cutout relay interrupts and locks out the ac control
bank.
power circuit in the load bank. If the CONTROL
CIRCUIT toggle switch (7, fig. 7-62) is in the ac
Emergency Shutdown Procedure
position, the ac load is dropped. The
OVER-VOLTAGE RESET toggle switch (6) on the ac
To shut down the load bank in an emergency,
panel does not reset the control power circuit unless the
proceed as follows:
input voltage is less than 125 volts.
1. Place the CONTROL CIRCUIT switch (7, fig.
7-62) in the OFF position. This action drops all
Underfrequency Cutout
loads and turns off the control power circuit in
the load bank.
If the frequency of the ac input from the power
plant is less than 370 Hz, a cutout relay interrupts and
2. Place all toggle switches on all control panels to
locks out the ac control power circuit in the load bank.
the OFF position.
If the CONTROL CIRCUIT toggle switch (7, fig.
3. Turn the VARIABLE 0-55 AMPS controls (1
7-62) is in the ac position, the ac load is dropped. The
and 4, fig. 7-62) fully counterclockwise.
UNDERFREQUENCY RESET toggle switch (10) on
the ac panel does not reset the control power circuit
CAUTION
unless the frequency is greater than 377 Hz.
This course is intended only to familiarize you with
Cooling Airflow Failure
equipment operation. Because of support
equipment changes and manufacturer's updates,
Two wind switches in the load bank sense the flow
proper procedures may change. Always consult the
of cooling air through the load bank assemblies. If this
technical manual for proper operating procedures.
flow of air is reduced by obstructions, such as blockage
Operating procedures for both the MLB1 and the
of inlet louvers or closed exhaust doors, or a fan
DA-675/MSM are also attached to the inside cover
malfunctions, the wind switches extinguish the WIND
of the control panels.
SWITCH CLOSED indicator (6, fig. 7-62) and cut out
the control power circuit, thereby dropping all loads.
The fans continue to operate, however, unless there is a
FAILURE OF THE LOAD BANK TO
defect in one or both.
OPERATE
Thermal Overload
The following text provides guidance for the
operator in situations where the load bank cannot be
Four temperature-sensitive switches in the load
started or ceases to operate during a power plant test
bank sense the temperature in the load bank
procedure.
assemblies. If the temperature becomes excessively
high, these switches cut out the control power circuit,
DC Overvoltage Cutout
thereby dropping all loads. The fans, meanwhile, will
continue to operate. When the temperature drops to
If the dc-volt voltage applied to the aircraft
normal, the switches automatically reset, restoring
servicing input from the power plant exceed 31 volts, a
control power.
cutout relay interrupts and locks out the dc control
7-66
