Cummins/Onan — Insulation Resistance Testing
Maintenance · Generator windings
From a Cummins/Onan service manual covering: 1000DFHD-60 / 900DFHD-50, 750DFHA-60 / 620DFHA-50, 800DFHB-60 / 700DFHB-50, 900DFHC-60 / 800DFHC-50. Check it applies to your exact model before use.
Applies to: Cummins/Onan DFHA, Cummins/Onan DFHB, Cummins/Onan DFHC, Cummins/Onan DFHD, Cummins/Onan QST30 engine, Cummins/Onan QST30-G1 engine, Cummins/Onan QST30G2 engine, Cummins/Onan QST30-G3 engine, MTU QST30G3 engine
Procedure
- Disconnect plug J10 from the voltage regulator output stage module.
- Disconnect the AC control input leads (marked 5, 6, 7 and 8) from the generator output terminals.
- If the RTD option is installed, ground all six RTD temperature leads (18 leads total).
- Apply test potential between the winding and ground (winding laminations).
- Compare readings with Table 6-1; investigate and correct low readings before returning to service.
Tools required
- 500 VAC megger Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- P7 frame: main stator, main rotor, PMG, exciter stator 10.0-1.0 MEG at 500 VDC setting
- HC6 frame: 5.0-1.0 MEG at 500 VDC setting
Full service-parts list: Cummins/Onan DFHA →, Cummins/Onan DFHB →, Cummins/Onan DFHC →, Cummins/Onan DFHD →
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.