Introduction

NOTE: For Specifications with illustrations, make reference to Specifications For 3406 Spark Ignited Engine Attachments, Form No. SENR3868. If the Specifications in Form SENR3868 are not the same as in the Systems Operation and Testing And Adjusting, look at the printing date on the back cover of each book. Use the Specifications given in the book with the latest date.

Electrical System

Two electrical systems are available to provide engine protection. In each case, engine shutoff is achieved by grounding the magneto. Each system is also capable of activating the gas shutoff valve if provided.

1. For the self-powered protection system, oil pressure (OP) and water temperature (WT) protection are provided. When combined with a mechanical overspeed contactor switch (MOS) [(provided standard on engine)], full protection is obtained. An energized-to-shutoff (ETS) gas shutoff valve (GSOV) is available which is activated by magneto voltage.

2. An energized-to-run (ETR) non-auto-start-stop protection system provides OP, WT and OS (overspeed) protection. An electronic speed switch (ESS) is used for the OS protection. This system is fully independent and requires an external 24 volt power source and an energized-to-run (ETR) gas shut-off valve.

Electrical Schematics And Wiring Diagrams

Electrical schematic foldouts are provided in this section with the text for each protection system. Use the electrical schematics to follow the circuit operations of the protection systems.

Point-to-point wiring diagrams for the protection systems, junction boxes, and starting, charging, and tachometer circuits are located in the Wiring Diagrams Section of this module. Use the diagrams for component position layout.

Components

The components that follow may be used on one or more of the two protection systems available on the 3406 spark ignited engine.

Electric Service Meter

The electric service meter group is self-powered. A magnetic pickup mounted on the flywheel housing provides voltage (starting at 200 engine rpm) to power the electric service meter which records clock hours with quartz accuracy. A separate magnetic pickup must be used for each service meter; it cannot be shared with the digital tachometer, electronic speed switch, or electronic governor magnetic pickup.

Water Temperature Contactor Switch (WTS)

A water temperature contactor switch is located in the cooling system. The unit is nonadjustable. Thermal expansion of the element operates a micro-switch that signals the shutoff solenoid which causes engine shutdown. The water temperature element must be in contact with the coolant. If overheating occurs due to low coolant level or no coolant, the sending unit will not function.

The water temperature sending unit can also be wired into an alarm system or light to signal high water temperature. After an overheated engine is allowed to cool, the contactor automatically resets itself.

Contactor Switch (Water Temperature)

Magnetic Pickup (MPU)

Magnetic Pickup
(1) Clearance dimension. (2) Magnetic pickup. (3) Wires. (4) Locknut. (5) Gear tooth. (6) Housing.

The magnetic pickup is a single pole, permanent magnet generator made of wire coils around a permanent magnet pole piece. As the teeth of the flywheel ring gear go through the magnetic lines of force around the pickup, an AC voltage is made. A positive voltage is made when each tooth goes by the pole piece. Each time the space between the teeth goes by the pole piece, a negative voltage is made. Engine speed is then determined by the frequency of these signals.

Mechanical Overspeed Switch (MOS)

The overspeed contactor is used in a self powered protection system to protect the engine from damage due to overspeeding. It contains a micro switch that is activated by high engine speed. The overspeed switch is mounted on the tachometer drive. If the engine overspeeds, the switch contacts close and connect the magneto to ground to shut down the engine. When the engine shuts down because of overspeeding, the overspeed contactor switch must be reset by pushing reset button. The overspeed contactor switch is adjustable.

Circuit Breaker (CB)

The circuit breaker is a switch that opens the battery circuit if the current in the electrical system goes higher than the rating of the circuit breaker.

A heat activated metal disc with a contact point completes the electric circuit through the circuit breaker. If the current in the electric system gets too high, it causes the metal disc to get hot. This heat causes a distortion of the metal disc which opens the contacts and breaks the circuit. A circuit breaker that is open can be reset after it cools. Push the reset button to close the contacts and reset the circuit breaker.

Circuit Breaker Schematic
(1) Reset button. (2) Disc in open position. (3) Contacts. (4) Disc. (5) Battery circuit terminals.

Oil Pressure Switch (OPS)

Oil Pressure Switch

The oil pressure switch uses a spring loaded piston to activate a micro switch for a specific pressure rating. This type of switch has better accuracy over the operating temperature range and uses a much higher electrical contact rating to improve reliability.

Slave Relay (SR)

This is a standard type relay that, when energized, has contacts that open across one circuit and close across another circuit. The circuits are wired so that voltage from the magneto goes to the spark plugs when the relay is energized. When not energized, the relay causes magneto voltage to go to ground. This relay is not used on the self-powered protection system.

Emergency Stop Switch (ES)

The emergency stop switch has two normally closed contacts. When pressed, magneto voltage is grounded and the gas shutoff valve (GSOV) is closed. The engine will be prevented from starting until the switch is manually reset.

Electronic Speed Switch (ESS)

Electronic Speed Switch (ESS)
(1) Verify button. (2) Reset button. (3) "LED" overspeed light. (4) Seal screw plug (overspeed). (5) Seal screw plug (crank terminate).

The Electronic Speed Switch (ESS) is designed with controls built into a single unit to monitor several functions at the same time. The functions that the ESS monitors are:

Engine Overspeed (OS)

This is an adjustable engine speed setting (normally 118% of rated speed) that prevents the engine from running at a speed that could cause damage. This condition will cause a switch to close that shuts off the fuel to the engine and connects the magneto to ground to stop current flow to the spark plugs.

Crank Termination (CT)

This is an adjustable engine speed setting that signals the starter motor that the engine is firing and cranking must be terminated. When the speed setting is reached, a switch will open to stop current flow to the starter motor circuit. The starter motor pinion gear will now disengage from the engine flywheel ring gear.

Junction Box

Junction Box (Box For External Powered Shutdown Shown)
(1) Terminal strips (TS). (2) Location for electric speed switch (ESS). (3) Emergency stop switch (ES). (4) Location for slave relay (SR). (5) Stop-bypass switch (SBS) (6) Location for circuit breakers (CB).

Two junction boxes are used on the engine, one for a powered protection system as pictured and one for a self powered protection system. The junction box contains the terminal strips (TS), location for electric speed switch (ESS), emergency stop switch (ES), location for slave relay (SR), stop-bypass switch (SBS) and circuit breaker (CB). It also has an oil pressure switch (OPS) located in the back. The junction box for the self powered protection system contains a terminal strip TS), ignition adapter (IA) and a stop-bypass switch (SBS).

NOTE: The start-bypass switch is always located on the J box cover. A start-bypass switch may also be located on the bracket below the instrument panel on the right side of the engine or underneath the gauge panel.

Self-Powered Protection System

This system requires no external power for electrical protection. When started (by a separate system), the engine is protected from low oil pressure fault (OP) and high water temperature fault (WT). Overspeed protection (OS) is provided with a mechanical overspeed contactor switch wired into the system. An optional energized-to-shutoff gas valve (GSOV) is available for this system.

The junction box for this system contains a stop-bypass switch (SBS), and an ignition adapter (IA).

To follow the circuit operations of this protection system, refer to Electrical Schematic For Self-Powered Protection at the end of this text.

The point-to-point wiring diagrams for this protection system and junction box are located in the Wiring Diagrams section of this module.

Circuit Operation: No Faults

Engine Stopped

With the engine stopped, no electrical power is available to the system. The water temperature switch (WTS) and mechanical overspeed switch (MOS) are in their normally open positions. Oil pressure switch (OPS) is in its normally closed position.

Engine Startup

When the engine is started (by a separate system), the start-bypass switch must be held in the bypass (up) position (open between contacts SBS-2 & 3 and between SBS-5 & 6) until engine oil pressure is obtained. Magneto voltage is not allowed to travel to ground.

If the start-bypass switch is not held in the bypass position before oil pressure is achieved, magneto voltage will be allowed to travel through closed contacts SBS-2 & 3, through the closed oil pressure switch OPS and then to ground. The voltage traveling through the gas shutoff valve (if so equipped) energizes the valve coil, shutting off the gas to the engine. At the same time, the circuit between contacts GSOV-1 & 3 opens and the circuit between contacts GSOV-1 & 5 closes. This also grounds the magneto voltage, preventing spark to the cylinders.

Once oil pressure is achieved, oil pressure switch OPS will open and the start-bypass switch can be allowed to return to run (center) position (closed contacts between SBS-2 & 3, open contacts between SBS-4 & 5). Magneto voltage is not allowed to travel to ground.

Engine Running

When the engine is running with no problems, magneto voltage is not grounded. The oil pressure switch (OPS), water temperature switch (WTS) and mechanical overspeed switch (MOS) are all open. No magneto voltage is felt by the valve coil of the gas shut-off valve (GSOV), therefore gas is allowed to the engine.

Engine Normal Stop

The operator stops the engine by pressing the start-bypass switch to the stop (down) position to close contacts SBS-5 & 6. This allows the magneto voltage to go to ground, preventing spark at the cylinders. The valve coil of the gas shut-off valve (if so equipped), energized by the magneto voltage, then shuts off the gas supply. At the same time, the circuit between contacts GSOV-1 & 3 opens and the circuit between contacts GSOV-1 & 5 closes, grounding the magneto voltage.

Show/hide table

To prevent personal injury due to accidental starting of the engine, disconnect the batteries during maintenance or repair work.

Before starting the engine again, do the steps that follow:

1. Correct any faults that may have been the cause of the emergency shutdown.

Show/hide table

Unburned gas left in the manifold can ignite when the engine is restarted.

2. Before restarting any gas engine which was stopped by grounding the magneto, crank the engine with the gas valve turned off, and the magneto grounded, for 10 to 15 seconds. This will clear the unburned gas from the exhaust system.

3. Manually reset the gas shut-off valve (if so equipped).

4. Start the engine again while holding the start-bypass switch (SBS) in the up (bypass) position until oil pressure is achieved.

Fault Circuit Operation

Low Oil Pressure (OP), Coolant Overheating (WT), Engine Overspeed (OS)

When the engine is running, any one of the following faults will cause magneto voltage to be grounded through the respective switch:

1. Oil pressure drops below setting of oil pressure switch (OPS) and causes it to close.

2. Coolant temperature exceeds setting of water temperature switch (WTS) and causes it to close.

3. Engine increases above the overspeed setting of the mechanical overspeed switch (MOS) and causes it to close. The (MOS) must be reset if this occurs to unground the ignition.

When the magneto is grounded, spark is no longer available to the cylinders. Magneto voltage going to any of the closed switches also energizes the gas shut-off valve (if so equipped). The energized GSOV then shuts off the gas supply. At the same time, the circuit between contacts GSOV-1 & 3 opens and the circuit between contacts GSOV-1 & 5 closes, grounding the magneto voltage.

Show/hide table

Unburned gas left in the manifold can ignite when the engine is restarted.

Before restarting any gas engine which was stopped by grounding the magneto, crank the engine with the gas valve turned off, and the magneto grounded, for 10 to 15 seconds. This will clear the unburned gas from the exhaust system.

Refer to these notes and abbreviations when using Electrical Schematic for Self-Powered Protection and Powered Protection.

NOTE F: Attach ground wire to ground strap bolt on junction box mounting bracket.

NOTE H: When starting engine, stop-bypass switch must be held in up position until oil pressure is achieved. Failure to do so will result in engine shutdown.

NOTE P: Remove jumper between terminal points TS-2 and TS-3 when gas shutoff valve is used.

Powered Protection System

This full independent system requires external 24 VDC power for electrical engine protection. The engine is monitored for engine overspeed (OS) oil pressure (OP) and water temperature (WT). The gas shutoff valve (GSOV), if provided, is energized to run (ETR).

The junction box contains an electric speed switch (ESS), slave relay (SR1), oil pressure switch (OPS1), circuit breaker (CB5) and emergency stop switch (ES). With this system, the slave relay remains energized in order for the engine to run.

The point-to-point wiring diagrams for this protection system and junction box are located in the Wiring Diagrams section at the end of this text.

Circuit Operation: No Faults

Engine Stopped

With the engine stopped, power is always available across terminals 5 and 6 (line 54) of electronic speed switch (ESS). At this time all switches are in their normally open or normally closed positions.

Engine Start-up (with electric start)

When the engine mounted start stop switch (EMSSS) is moved to the START position, the circuit to the starter motor is closed across terminals EMSSS-1 and EMSSS-3 (line 3). The starting motor pinion solenoid (PS) (line 3) is energized and closes its contact to energize the starting motor (SM) (line 2).

At the same time, current flows from EMSSS-3 through diode 4 (line 12) to slave relay 1 (SR1) (line 37) arming SR1 and also energizing the energized-to-run gas shutoff valve (GSOV) (line 40). The energized SR1 opens its contacts across terminals SR1-1 and SR1-2 (lines 45 and 47) and closes its contacts across terminals SR1-1 and SR1-3 (lines 45 and 43) preventing the magneto (MAG) from being grounded.

When the engine starts to run and the crank termination speed setting is reached, electronic speed switch (ESS) crank terminate switch (CT) opens its contacts across terminals ESS-11 and ESS-12 (line 17) and closes its contacts across terminals ESS-10 and ESS-11 (line 18).

When ESS(CT) contacts open across terminals ESS-11 and ESS-12, current flow is stopped to the starter motor circuit and the starter motor (SM) will now stop.

At this point, the engine has started to run. Crank termination setting is reached, but oil pressure is not yet achieved. The EMSSS is still held in the START position. Current is flowing through ESS (CT) terminals ESS-11 and ESS-10, ESS(OS) terminals ESS-8 and ESS-9 (line 30), ES terminals ES-1 and ES-2 (line 19), WTS terminals WTS-2 and WTS-3 (lines 19 and 20), and EMSSS terminals EMSSS-1 and EMSSS-2 (line 4). Oil pressure switch OPS1, open at terminals OPS1-1 and OPS1-2 (line 13) due to low oil pressure, is bypassed.

When oil pressure is achieved, oil pressure switch contact terminals OPS1-1 and OPS1-3 will open and terminals OPS1-1 and OPS1-2 will close. The EMSSS switch can be released to its normal ON position, to close contacts across terminals EMSSS-1 & EMSSS-2 (line 4). OPS1 is now included in the circuit, and full protection (OP, WT, OS) is in effect.

Engine Start-up (no electric start)

On the front of the junction box door is a stop-bypass switch (SBS) spring loaded to the run position. When the engine is started (by a separate system), the stop-bypass switch must be held in the bypass (up) position (open contacts between SBS-2&3, SBS-5&6 and SBS-11&12) until engine oil pressure is obtained. Magneto voltage is not allowed to travel to ground.

If the stop-bypass swutch (SBS) is not held in the bypass position before oil pressure is achieved, voltage will not travel through the open contacts SBS-10&11, which energizes the slave relay (SR1) and provided current to the to the energized-to-run gas shutoff valve (GSOV). This prohibits gas flow to the engine. Also, since the slave relay is de-energized, contacts SR1-1&2 are closed which allows magneto voltage to flow to ground.

When the engine starts to run and the crank termination speed setting is reached, electronic speed switch (ESS) crank terminate switch (CT) opens its contacts across terminals ESS-11 and ESS-12 (line-17) and closes its contacts across terminals ESS-10 and ESS-11 (line 17).

At this point the engine has started to run, but oil pressure is not yet achieved. The stop-bypass switch (SBS) is still help up in the bypass mode. Current is flowing through ESS (CT) terminals ESS-11&10 (line 17), ESS (OS) terminals ESS-8&9 (line 29), ES terminals ES-1&2 (line 18), WTS terminals WTS-2&3 (lines 18&19) and SBS terminals SBS-10&11 (line 24). Oil pressure switch OPS1, open at terminals OPS1-1&2 (line 13) due to oil pressure is bypassed.

When oil pressure is achieved, oil pressure switch contact terminals OPS1-1 and OPS1-3 will open and terminals OPS1-1 and OPS1-3 will open and terminals OPS1-1 and OPS1-2 will close. The SBS switch can be released to its normal RUN position, to close contacts across terminals SBS-11&12 (line 24). OPS1 is now included in the circuit, and full protection (OP, WT, OS) is in effect.

Engine Running

With no engine problems and engine running, oil pressure switch (OPS1) (line 13) is closed across contacts OPS1-1 and OPS1-2, so there is still current flow to energize slave relay SR1 (line 36) and gas shutoff valve GSOV (line 39). The engine will continue to run with these conditions.

Engine Normal Stop

The operator stops the engine by turning the engine mounted start-stop switch (EMSSS) to the OFF position on electric start or by pressing the stop-bypass switch (SBS) down to the STOP position. This stops current flow through the OPS1 (line 13) terminals OPS-1&2. With no current from OPS1, the gas shutoff valve (GSOV) (line 39) closes and SR1 (line 36) is de-energized. SR1 contact terminals SR1-1&3 open and terminals SR1-1&3 close, grounding the magneto (MAG) and preventing spark from reaching the cylinders.

After complete engine shutdown is accomplished, the electronic speed switch ESS(CT) closes across terminals ESS-11 and ESS-12 (line 17) to allow for restart. The engine can now be immediately restarted.

Emergency Stop Switch (ES)

The emergency stop switch (ES) is a red, mushroom shaped pushbutton that is located on the front of the junction box door. This pushbutton will shut the engine down and will also prevent the engine from being restarted, because it locks in the OFF (in) position.

When pushed in, ES creates an open circuit across contacts ES-1 and ES-2 (line 18). Flow of current is stopped to SR1 (line 36) and GSOV (line 39). The energized-to-run gas valve closes. At the same time, relay SR1 closes its contact between SR1-1 and SR1-2 (line 47) to connect the magneto (MAG) to ground and stop current flow to the spark plugs.

Show/hide table

To prevent personal injury due to accidental starting of the engine, disconnect the batteries during maintenance or repair work.

Before starting the engine again, do the steps that follow:

1. Correct any faults that may have been the cause of the emergency shutdown.

Show/hide table

Unburned gas left in the manifold can ignite when the engine is restarted.

2. Before restarting any gas engine which was stopped by grounding the magneto, crank the engine with the gas valve turned off, and the magneto grounded, for 10 to 15 seconds. This will clear the unburned gas from the exhaust system.

3. Make sure the ES has been reset (pushbutton is out) on the engine junction box. To reset, turn the pushbutton in the direction shown on the button face.

4. Restart the engine.

Fault Circuit Operation

Low Oil Pressure (OP), Coolant Overheating (WT), Engine Overspeed (OS)

When the engine is running with no problems, electric current for gas shutoff valve (GSOV) and slave relay (SR1) travels through ESS overspeed ESS(OS), water temperature switch (WTS), and oil pressure switch (OPS1). Any one of the following faults will stop current flow to GSOV and SR1. When de-energized, GSOV will close to shut off gas and SR1 will cause the magneto (MAG) to be grounded to prevent spark to the cylinders.

1. Oil pressure drops below rating of OPS1, causing contacts between terminals OPS1-1 and OPS1-2 (line 13) to open.

2. Coolant temperature exceeds setting of WTS, causing contacts WTS-2 and WTS-3 (line 18) to open.

3. Engine speed increases above the overspeed setting of ESS(OS), opening contacts ESS-8 and ESS-9 (line 29).

NOTE: A reset button on the ESS must be pushed to open the overspeed switch ESS(OS) before the engine can be restarted.

Show/hide table

Unburned gas left in the manifold can ignite when the engine is restarted.

Before restarting any gas engine which was stopped by grounding the magneto, crank the engine with the gas valve turned off, and the magneto grounded, for 10 to 15 seconds. This will clear the unburned gas from the exhaust system.

2301 Electric Governor Control System

When the 2301 Electric Governor Control (EGC) is used, all components of the protection system are activated in the same way as discussed with the nonelectric governors.

Wiring Diagrams

Engine Protection Systems (Starting, Charging, and Tachometer Circuits)

This section contains point-to-point wiring diagrams for the engine protection systems and starting, charging, and tachometer circuits.

These diagrams can be helpful for the user who is not familiar with the electrical schematic-type format, or who is interested in the component position layout for replacement purposes.

Refer to the notes and abbreviations on this page when using the wiring diagrams in this section. See the chart on the following page for the battery cable size.

NOTE A: Cable to be grounded at tachometer only when used without electric speed switch. Ground cable at speed switch when available.

NOTE B: Grounded system required for proper operation of shut-off system.

NOTE C: If 2301 Governor is used, only one magnetic pick-up is required. Use magnetic pick-up from speed switch. Connect mag pick-up to speed switch and then to 2301 Governor Control. Do not use multiple grounds on any particular length of shielded cable.

NOTE D: If electric starting motor is not used, connect positive lead of 24 VDC power source to TS-1 on junction box terminal strip and negative to TS-28.

NOTE E: Diagrams and schematics for junction box wiring shipped inside junction box.

NOTE F: Attach ground wire to ground strap bolt on junction box mounting bracket.

NOTE G: Refer to Chart B for engine start-stop switch operating schematic.

NOTE J: Attach ground wire to start-stop switch mounting bracket bolt.

NOTE L: Start-stop switch required with oil pressure, water temp, overspeed protection system only when used in a non-auto-start-stop application.

NOTE P: Remove jumper between terminal points TS-2 and TS-3 when gas shutoff valve is used.

Wiring Diagram Self-Powered Protection

Wiring Diagram ETR, Powered Protection System

Junction Box Wiring Diagrams

This section contains point-to-point wiring diagrams for the junction boxes used with the engine protection systems. These diagrams can be helpful for the user who is not familiar with the electrical schematic-type format, or who is interested in the component position layout for replacement purposes.

NOTE: The junction boxes for the ETR independent and ETR auto-start-stop protection systems are used for other engines in addition to the spark-ignited 3406. Therefore, some components shown in the junction box wiring diagrams for the ETR protection systems will not apply to the spark-ignited 3406.

Refer to the abbreviations on this page when using the wiring diagrams in this section.

Water Temperature, Oil Pressure, Mechanical Overspeed Protection-No External Power Source

Junction Box Wiring Diagram Self-Powered Protection

NOTE: WHEN STARTING ENGINE, STOP-BYPASS SWITCH MUST BE HELD IN UP POSITION UNTIL OIL PRESSURE IS ACHIEVED. FAILURE TO DO SO WILL RESULT IN ENGINE SHUTDOWN.

Junction Box Wiring Diagram ETR, Powered Protection, f/u/w Electric Start

Junction Box Wiring Diagram ETR, Powered Protection, n/f/u/w Electric Start