Cummins/Onan LS-15M — Megger and Polarization Index (PI) Test
Testing & diagnosis · Generator windings
For the Cummins/Onan LS-15M, from the Cummins/Onan service manual.
Applies to: Cummins/Onan DFAA, Cummins/Onan DFAB, Cummins/Onan DFAC, Cummins/Onan DFBF, Cummins/Onan DFCB, Cummins/Onan DFCC, Cummins/Onan DFCE, Cummins/Onan DFE
Before you start
- The windings of medium-voltage (601 through 15,000 volts) generator sets must be dry before the generator is operated.
- Further H.V. testing may degrade the insulation; if required, test voltage = 0.8 (2 x rated voltage + 1000).
Procedure
- Perform the Generator Set Grounding Procedure.
- Disconnect plug J10 from the voltage regulator output stage module and the AC control input leads (marked 4, 5, 6, 7 and 8).
- If RTD option is installed, ground all six RTD temperature leads (18 leads total).
- Perform Insulation Resistance Test and PI Test for the desired windings.
- PI is ratio of ten minute reading in megohms divided by one minute reading; ratio of two or greater is good.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Megger test applies voltage for up to one minute
- PI test applies voltage between winding and ground for ten minutes
Full service-parts list: Cummins/Onan DFBF →, Cummins/Onan DFCC →, Cummins/Onan DFCE →, Cummins/Onan DFE →
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.