When the electric protection system detects an unsafe limit, the system energizes or the system de-energizes the fuel solenoid or the 2301A Electric Governor Control. An unsafe limit is called a fault.
The basic difference between the ETR protection system and the ETS protection system is the operation of the fuel solenoid. The ETR system de-energizes the fuel solenoid in order to stop the fuel flow which causes engine shutdown. The ETS system energizes the fuel solenoid in order to stop fuel flow which causes engine shutdown.
The ETR protection system requires the fuel solenoid to be energized in order for the engine to run. The fuel solenoid must be energized before the fuel is allowed to flow to the engine cylinders. After the engine starts and runs, a normal shutdown or a problem with any of the engine functions that are monitored will cause the fuel solenoid to be de-energized. When the fuel solenoid is de-energized, the fuel flow to the cylinders is stopped. This action causes engine shutdown.
The ETS protection system requires the fuel solenoid to be de-energized in order for the engine to run. The fuel solenoid must be de-energized before the fuel is allowed to flow to the engine cylinders. After the engine starts and runs, a normal shutdown or a problem with any of the engine functions that are monitored will cause the fuel solenoid to be energized. When the fuel solenoid is energized, the fuel flow to the cylinders is stopped. This action causes engine shutdown.
The 2301A Electric Governor Control operates in the same manner on the ETR protection system or on the ETS protection system. When the electric governor control system is installed, the fuel solenoid is not used. When a fault occurs, the electric governor control system is de-energized. This causes the fuel control linkage to stop the fuel flow to the engine.
The ETR protection system and the ETS protection system use two or three engine components in order to monitor as many as six engine operating functions:
- Engine overspeed (OS) which is monitored by the electronic speed switch
- Crank termination which is monitored by the electronic speed switch
- Oil step latch which is monitored by the electronic speed switch (3500 Series Engines)
- Engine oil step pressure which is monitored by the electronic speed switch (3500 Series Engines)
- Water temperature (WT) which is monitored by the water temperature contactor switch
- Oil pressure (OP) which is monitored by one or two oil pressure switches.
Overspeed protection monitors the engine from starting through 118% of rated speed. An engine that has all three of the components is called a Full Protection System.
An engine which does not have an electronic speed switch is called Partial Protection because the electric protection system does not have overspeed protection. Partial Protection has only oil pressure protection and water temperature protection.
Two options for the switchgear are available. The first option does not require the switchgear. The second option requires the switchgear in order for the electric protection system to function. The switchgear can be purchased from Caterpillar or other suppliers.
Five basic junction box arrangements are available. The arrangements are listed in the table. Variations to these basic arrangements are produced when optional attachments are purchased with the engine. An automatic air shutoff and a starting aid switch are examples of optional attachments.
| Basic Junction Box Arrangements | ||
| Engine Model | Switches | Switchgear that is provided with the engine |
| 3200-3400 | OP, WT, and OS | No |
| 3200-3400 | OP and WT | No |
| 3200-3400 | OP, WT, and OS | Yes |
| 3500 | OP, WT, and OS | No |
| 3500 | OP, WT, and OS | Yes |