ARMY TM 9-6115-644-24
AIR FORCE TO 35C2-3-446-12
MARINE CORPS TM 09249A/09246A-24/2
1-12-1-1 The Fault System (FIGURE 1-2) protects the generator set and any connected load against the potential faults
described below and provides an indication of any incurred fault. The following summary of the Fault System will assist
in understanding the operation of the other generator set systems. Additional details relating to specific protection devices
are also provided in the descriptions of the respective systems.
1-12-1-2 The Fault System consists of the malfunction indicator, low fuel level float switch, fuel float switch module, fuel
level relay, low oil pressure switch, coolant high temperature switch, overvoltage relay, overload/short circuit relay, over-
speed switch, overspeed relay, OVERSPEED RESET switch, undervoltage relay, reverse power relay, engine fault relay,
electrical fault relay, and BATTLE SHORT switch. In addition to the fault indicator lamps, the malfunction indicator includes
the PUSH TEST & RESET LAMPS switch which when depressed, illuminates all the lamps and resets any fault indication.
1-12-1-3 Activation of any one of the following protection devices will cause three events to occur. The AC circuit inter-
rupter relay will open; the generator set engine will be shut down; and a fault indicator lamp will be illuminated to show
which malfunction occurred.
1-12-1-3-1 Coolant High Temperature Switch. This device will activate when the engine coolant leaving the engine ex-
ceeds 225 ± 5° F (107 ± 3° C).
1-12-1-3-2 Low Oil Pressure Switch. This device activates when the engine lubrication oil pressure falls below 15 ±
3 psi (103.4 ± 20.7 kPa).
1-12 -1-3-3 Low Fuel Level Float Switch. This device will activate when the fuel level falls to a point at which the operating
time of the set at rated load is four minutes.
1-12-1-34 Overvoltage Relay. This device will activate when the 120-volt generator coil winding has risen to and re-
mained at any value greater than 153 ± 3 volts.
1-12-1-3-5 Overspeed Relay. This device will activate when the engine speed exceeds 2200 ± 40 RPM.
1-12-14 Fuel Float Switch Module.
This device prevents inadvertent engine shutdown by providing a one second delay after actuation of the Iow fuel level float
1-12-1-5 Electrical protection devices will cause two events to occur. The AC circuit interrupter relay will open, and a
fault indicator lamp will illuminate to indicate which fault occurred.
1-12-1-5-1 Short Circuit Relay. This device will activate when the set output current in any phase exceeds 425 percent
of the rated value.
1-12-1-5-2 Overload Relay. This device will operate when the load current in any phase exceeds 110 percent of rated
1-12-1-5-3 Undervoltage Relay. This device will activate instantaneously when the 120 volt generator coil winding has
dropped to 48 volts and will trip after time delay when the coil voltage drops below 99 volts.
1-12-1-54 Reverse Power Relay. This device will operate if power flow into the generator set exceeds 20 percent of rated
1-12-1-6 Although it is possible for more than one fault to occur at one time during operation, only the first fault to occur
will be displayed by the malfunction indicator. The activated indicator lamp circuit remains illuminated until the malfunction
indicator is reset. The lamp will be off with the MASTER SWITCH in the OFF position and will be reilluminated when the
MASTER SWITCH is turned to one of the RUN positions. Resetting a fault indication is done in two steps. First push the
PUSH TEST & RESET LAMPS switch located on the malfunction indicator. Then move the MASTER SWITCH to the OFF
position. After a shutdown due to engine overspeed, the OVERSPEED RESET switch must be actuated to reset the en-
gine electrical control circuit before the engine can be restarted.