Murphy Series A900 manual Provides a signal to the overspeed shutdown circuit if

6-1/2 in.

(165 mm)

Low Water	Overcrank
Temperature
Loss of Speed	Overspeed
Signal
Lamp Test	Oil Pressure
AUTO	Water
	Temperature

be turned off so no overcrank shutdown occurs.

(e)	Shutdown Time Delay Bypass; this delay prevents the oil
	pressure, water temperature and loss of speed signal
	shutdown circuits from operating for 15 seconds after the
	engine starts as detected by the crank disconnect circuit.
(f)	Overspeed Speed Switch;
	1. Provides a signal to the overspeed shutdown circuit if
	the engine exceeds the preset speed. The factory
	setting is approximately 3894 Hz, or 1980 RPM on an
	engine with 118 teeth on the flywheel ring gear. The

9-3/4 in.

OFF

adjustment range is 300 Hz to 10,000 Hz.

(248 mm)

TEST

Air Damper

Closed

Figure 3-5.1

2. A push to test switch is provided to allow testing of the

overspeed circuit without overspeeding the engine.

When switch is depressed, the set point of the speed

switch is lowered approximately 10%.

3. The push to test switch can also be used to set the

overspeed switch at approximately 110% of running

speed. Hold the switch depressed while adjusting the

setting until the overspeed trips. When switch is

released, the set point will be 10% above normal

running speed. This is the method used to make the

factory setting. With engine speed at 1800 RPM or

3540 Hz.

(g) Cooldown circuit; this circuit keeps the engine running

for five minutes after the transfer switch has removed

the load from the generator and signaled the A902-2 to

stop the engine. This feature may be selected (turned

On, standard setting is Off) with a switch on the back of

the Control / Display Module.

(c)TEST; turns on the engine controls and shutdown circuits. A start signal is applied to the automatic control and the engine start sequence begins.

3-5.1.2Lamp Test Pushbutton: Tests the lights on the A- 902-2 module.

3-5.1.3The A902-2 SELECTRONIC® Control Module includes the following engine control features:

(a)Cycle crank circuit; will crank the engine for 15 seconds then rest for 15 seconds until the engine starts. The crank/rest time is selectable for either 10, 15, 20, 25 or 30 seconds. If the engine false starts, goes above crank disconnect speed then drops below that speed, the control will rest for a fixed 10 second period before cranking again.

(b)Crank Disconnect Speed Switch; this circuit detects engine speed and terminates cranking when engine speed rise above the speed switch setting. The speed switch is adjustable, 25 Hz to 2000 Hz, and is factory set at 1180 Hz. This would be 600 RPM on an engine with 118 teeth on the flywheel ring gear.

(c)Auxiliary Crank Disconnect Circuit; this circuit, required by NFPA-110, is provided as a back up for the Crank Disconnect Speed Switch. It is operated by an external switch sensing either speed, generator voltage or some other variable that could be used to terminate cranking. Either circuit will disconnect the starter when the engine starts.

(d)Overcrank circuit; will stop automatic cranking and indicate overcrank if engine fails to start after 3 attempts. The number of cranks are selectable for 1, 2, 3, 4 or 5 cycles before shutdown. The overcrank circuit may also

3-5.1.4Seven (7) First-out Shutdown Circuits; provide first-out indication of cause of shutdown. These circuits deactivate the fuel relay and lockout the A902-2 until reset. Shutdown circuits are activated by the crank disconnect circuit and are not active when the engine is stopped. Six (6) Red Shutdown Indicating Lights are provided. The Remote Shutdown circuit does not have an indicator light.

(a)Overcrank; tripped by the overcrank sensing circuit which counts the number of cranking attempts.

(b)Overspeed; tripped by overspeed switch when engine exceeds a preset speed.

(c)Oil Pressure; tripped by the oil pressure SWICHGAGE® if pressure drops below preset point while the engine is running.

(d)Water Temperature; tripped by the water temperature SWICHGAGE® if engine coolant temperature exceeds the switch setting.

(e)Spare Shutdown; tripped by an external switch. This circuit is provided for an additional shutdown that may be recommended by the engine supplier.

(f)Loss of Speed Signal; tripped by an internal sensing circuit that detects the loss of the Magnetic Pickup frequency signal for the speed switches while the engine is still running. Since the Overspeed shutdown circuit is activated by the frequency input, it prevents the engine from running without overspeed protection.

(g)Remote Shutdown; this circuit is provided to shutdown the engine generator from a remote location. No

indicating light is provided.

3-5.1.5Two (2) Alarm Indicating Circuits; provide indication

9