Cummins/Onan — Circuit Breaker Insulation Resistance Check
Testing & diagnosis · AC load circuit breaker
From a Cummins/Onan service manual covering: 4BT3.9, 4BT3.9-GC1, 4BT3.9-GC2, 6BT5.9, 6BT5.9-GC1, 6BT5.9-GC2, 6CT8.3, 6CT8.3-GS/GC1, 6CTA8.3, 6CTA8.3-GS/GC1, 6CTA8.3-GS/GC2. Check it applies to your exact model before use.
Applies to: Cummins/Onan 4BT3.9, Cummins/Onan 6BT5.9, Cummins/Onan 6CTA8.3, Cummins/Onan 4BT3.9 engine, Cummins/Onan 6BT5.9 engine, Cummins/Onan 6CT8.3 engine, Cummins/Onan 6CTA8.3 engine
Procedure
- Disconnect load and line conductors; place breaker in On position.
- Use insulation resistance meter applying at least 500 volts to test leads.
- Measure insulation resistance between each pole, and to ground.
- Also test between line and load terminals with breaker in Off position.
- Reading less than 100,000 ohms indicates a ground; clean case surfaces and retest.
Tools required
- Insulation resistance meter (at least 500 volts) Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Reading less than 100,000 ohms indicates a ground
Source: Cummins/Onan service 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.