Generac — Test All Stator Windings to Ground (Insulation Resistance)
Testing & diagnosis · AC generator stator
From a Generac service manual covering: GN-190, GN-220, NP-30G, NP-40G. Check it applies to your exact model before use.
Applies to: Generac NP-30G, Generac GN-190 / GN-220 engine, Generac GN-220 engine
Before you start
- All Stator leads must be isolated from other components, especially circuit boards, before performing tests. The high voltages used in testing insulation resistance will damage electronic components.
Procedure
- Disconnect and isolate all Stator leads before starting tests.
- Connect the ends of all Stator leads together; make sure none touch any terminal or part of the generator.
- Connect one tester probe to the junction of all Stator leads and the other to a clean frame ground on the Stator.
- Apply a voltage of 1000 volts for about 1 second.
- If insulation resistance is low, clean and dry the Stator and repeat the test; if it fails again replace the Stator assembly.
Tools required
- Hi-Pot tester or Megohmmeter Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Test voltage 1000 volts for about 1 second
- Minimum insulation resistance (megohms) = generator rated volts / 1000 + 1 (e.g. 120 VAC = 1.12 megohms)
Full service-parts list: Generac NP-30G →
Source: Generac 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.