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Home›Repair guides›Caterpillar›Recommended Periodic Insulation Test Procedure

Caterpillar — Recommended Periodic Insulation Test Procedure

Maintenance · Generator Windings

From a Caterpillar owner's manual covering: 3306B, 3406, 3406E, 3412C, SR4B. Check it applies to your exact model before use.

Applies to: Caterpillar 3306B, Caterpillar 3406, Caterpillar 3406E, Caterpillar 3412C, Caterpillar SR4B

Before you start

  • Personal injury or death can result from electrocution. The megohmmeter applies a high voltage; discharge the leads before touching.

Procedure

  1. Take the generator out of service.
  2. Visually inspect the generator for moisture. If moisture exists, do not perform this insulation test. Dry the unit first.
  3. Inspect the installation. Determine the equipment that will be tested by the insulation tester.
  4. Discharge the capacitance of the windings.
  5. Disconnect T0 from ground.
  6. Disconnect the regulator sensing lead wires: 20, 22, and 24.
  7. Connect the insulation tester's RED lead to ground.
  8. Connect the insulation tester's BLACK lead to T0.
  9. For units 600 volts or less set the voltage to 500 Volts. For units more than 600 volts set the voltage to 1000 Volts.
  10. Use the 30/60 Time Resistance Method: apply voltage and observe readings at 30 seconds and 60 seconds.
  11. Record the 60 second reading corrected for temperature. Record temperature and humidity. Remove voltage.
  12. Evaluate the readings by comparing the 60 second resistance reading with previous readings taken under similar conditions.
  13. Switch the insulation tester to OFF to discharge the leads, then disconnect the insulation tester's leads.

Tools required

  • 142-5055 Insulation Testing Gp Amazon
  • 9U-6003 Insulation Testing Gp Amazon

Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.

Specs & values

  • If a 60 second resistance reading has a 50 percent reduction from the previous reading, the insulation may have absorbed too much moisture

Full service-parts list: Caterpillar 3406 →, Caterpillar 3406E →, Caterpillar 3412C →, Caterpillar SR4B →

Source: Caterpillar owner's manual. Steps and values are as documented; always cross-check against the official manual and any later revisions for your exact serial number before servicing.

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