Caterpillar — Insulation - Test
Testing & diagnosis · Generator windings
From a Caterpillar owner's manual covering: C3.3, C3.3 Rental Generator Set, C4.4, C4.4 Rental Generator Set, D4D1-Up, GLE1-Up, N3X1-UP, N4R1-Up, N4X1-Up, X3B1-UP, XYC1-Up, XYD1-Up. Check it applies to your exact model before use.
Applies to: Caterpillar C3.3, Caterpillar C4.4
Before you start
- Personal injury or death can result from electrocution
- Do not touch the instrument leads without first discharging them
- When finished testing also discharge the generator windings
Procedure
- Isolate the generator. Ensure windings are free of moisture and at room temperature.
- Main Armature (Stator L4): open the line circuit breaker or load connections T1, T2, T3, T0.
- Prevent wires from contacting each other or ground. Isolate main armature from the voltage regulator.
- Connect one test lead to the generator enclosure (ground) and the other to generator lead T0.
- Insulation resistance must be one megohm or more.
- Exciter Field (Stator L1): disconnect wires 5+ and 6-.
- Connect megohmmeter between generator enclosure (ground) and exciter field lead (5+ or 6-).
- Exciter field insulation resistance must be a minimum of 0.25 megohm (250000 ohms).
- Exciter Armature (Rotor L2): disconnect the three wires of the exciter armature from the rectifier blocks.
- Connect one test lead to the rotor shaft and the other to any one exciter field lead.
- Insulation resistance must be a minimum of 0.25 megohm (250000 ohms).
Tools required
- 142-5055 Insulation Tester Megohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
Full service-parts list: Caterpillar C3.3 →, Caterpillar C4.4 →
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.