Cummins/Onan — Measuring Insulation Resistance
Testing & diagnosis · stator / rotor / control panel
From a Cummins/Onan service manual covering: P3200i, P4300i, P4300ie, RG 3200 IS, RG 4300 IS, RG2800i. Check it applies to your exact model before use.
Applies to: Cummins/Onan P3200i, Cummins/Onan P4300ie, Subaru EX21 engine, Subaru EX27 engine
Before you start
- Any part with insulation resistance less than 1 MΩ has faulty insulation and may cause electric leakage and electric shock; replace the faulty part.
Procedure
- Use a Cummins Onan generator tester in megger mode or a megger tester (500V range).
- Connect the tester to one receptacle output terminal and the ground terminal.
- Measure the insulation resistance.
- If below normal, disassemble and measure stator, rotor and control panel individually.
- For stator, check resistance between red lead and core, blue lead and core, and white lead and core.
- For control panel, measure resistances between live parts and grounded parts.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Insulation resistance of 1 megohm or more is normal
- Original insulation resistance at shipment is 10 megohm or more
Full service-parts list: Cummins/Onan P4300ie →
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.