METER GP-SERVICE 4W5556 - Caterpillar

Two basic electrical systems are available to provide engine protection: self-powered and powered by an external source. Protection from low engine oil pressure, high coolant temperature, and engine overspeed is provided. In both types of systems, engine shutoff is achieved by grounding the ignition system. Both systems are capable of activating a gas shutoff valve.For the self-powered system, protection from overspeed is provided by a mechanical overspeed switch. The gas shutoff valve (if equipped) is an energize-to-shutoff valve. The valve is activated by voltage from the ignition system.There are two basic types of protective systems that are powered by an external source. Both systems are energize-to-run systems: manual start/stop and automatic start/stop. An external power source of 24 volts is required for these systems. A gas shutoff valve is also required. An electronic speed switch provides protection from engine overspeed.For the automatic start/stop, the customer provides the cranking panel and the logic for starting and stopping.Junction Box
Illustration 1 g00776891
Inside of a typical junction box
(1) Terminal strips
(2) Electronic speed switch
(3) Emergency stop switch
(4) Run relay
(5) Circuit breakers The junction box contains terminal strips (1) and emergency stop switch (3). An engine oil pressure switch is located at the back of the junction box.The junction box may contain some other items according to the type of protection system that is used. The items may include the electronic speed switch (2) and run relay (4) for the gas shutoff valve. Circuit breakers (5) help to protect the electrical system from power surges.The junction box also contains the specific wiring diagram of the engine's electrical system.Self-Powered Protection System
This system requires no external power for electrical protection. The power is provided by the ignition system when the engine is running. The system is an energize-to-shutoff system. The engine is protected from low engine oil pressure, high water temperature, and overspeed. A gas shutoff valve (if equipped) will shut off gas to the engine when the valve is energized.Normal Operation
The junction box includes a bypass switch for starting, an emergency stop button, and an engine oil pressure switch.When the engine is stopped, no electrical power is available to the system. The engine oil pressure switch, the water temperature switch, and the mechanical overspeed switch are in the normally open positions.When the engine is started, the bypass switch must be held in the upward position until sufficient engine oil pressure is achieved. Otherwise, low engine oil pressure will prevent the engine from starting because the voltage from the ignition system will be grounded.When the engine is running without any problems, the ignition system is not grounded. The engine oil pressure switch, the water temperature switch, and the mechanical overspeed switch are in the normally open positions. When the switches are open, voltage is not supplied to the gas shutoff valve (if equipped).To stop the engine, turn OFF the gas supply. Press downward on the bypass switch in order to ground the ignition system.Engine Shutdowns
When the engine is running, any of the following shutoffs will cause the