BOLT 1004830 - Caterpillar

Recommended Periodic Insulation Tests
The high voltage that is produced by an operating generator set can cause severe injury or death. Before performing any maintenance or repairs, ensure that the generator will not start.Place the engine control switch in the "OFF" position. Attach "DO NOT OPERATE" tags to all starting controls. Disconnect the batteries or disable the starting system. Lock out all switchgear and automatic transfer switches that are associated with the generator.
Table 1
Tools Needed
Part Number Part Name Quantity
300-8648 Insulation Testing Gp 1 Periodically, use an insulation tester to check the insulation resistance of the generator's main stator winding. The frequency of this test is determined by the generator's environment. Previous insulation tester readings will also determine the frequency of this test.Test the main stator windings with an insulation tester in the following situations:
The generator set is started for the first time.
The generator set is removed from storage.
The generator set is operating in a humid environment. Test every three months.
The generator set is not protected from the elements in an enclosed area. Test every three months.
The generator set is installed in an enclosed area. This area needs to be low in humidity and this area needs to have steady temperatures. Test every twelve months (minimum).
The generator set has not been run under load for three months. Test the generator set weekly. Use space heaters around the generator set if the generator is exposed to a sea water environment or if the humidity is above 75 percent. Also use space heaters if a test result was below 3 megohms.Space heaters must be used whenever the generator set is not under load. Space heaters must also be used whenever salt is present or whenever high humidity is present. Using a space heater in this fashion is the only way to maintain insulation tester readings above one megohm. Use space heaters only when the generator is not running.For additional information, refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".Recommended Procedure for the Insulation Test
Personal injury or death can result from electrocution.The megohmmeter is applying a high voltage to the circuit.To avoid electrocution, do not touch the instrument leads without first discharging them. When finished testing also discharge the generator windings.
Take the generator out of service.
Visually inspect the generator for moisture. If moisture exists, do not perform this insulation test. Dry the unit first. Refer to Special Instruction, SEHS9124, "Cleaning and Drying of Electric Set Generators".
Inspect the installation. Determine the equipment that will be tested by the insulation tester.
Discharge the capacitance of the windings.
Disconnect "T0" from ground.
Disconnect the sensing lead wires for the regulator. This may be accomplished by unplugging the harness connectors.
Disconnect the PT leads of the load share module.
Connect the insulation tester's Black lead to ground.
Connect the insulation tester's RED lead to "T0".
Set the voltage to the rated voltage of the generator.
Use the 30/60 Time Resistance Method:
Apply voltage.
Observe the readings at 30 seconds. Observe the readings at 60 seconds.
Record the 60 second reading. This reading must be