Generac — Stator Insulation Resistance Test
Testing & diagnosis · Stator windings
From a Generac service manual — check it applies to your exact model before use.
Applies to: Generac GH-410 engine, Generac GT-530 engine, Generac GT-530 engine, Generac GT-990 engine
Before you start
- All parts that might be damaged by the high megger voltages must be disconnected before testing.
Procedure
- Disconnect stator output leads 11 and 44 from the generator main line circuit breaker.
- Remove stator output leads 22 and 33 from the neutral connection and separate the two leads.
- Disconnect the C2 Connector from the side of the control panel.
- Connect the terminal ends of Wires 11, 22, 33 and 44 together, clear of the frame.
- Connect the red test probe of the Hi-Pot tester to the joined terminal ends; connect the black tester lead to a clean frame ground.
- Turn the Hi-Pot tester switch OFF; plug the tester cord into a 120 volt AC wall socket and set its voltage selector switch to "1500 volts".
- Turn the tester switch ON and observe the breakdown lamp. After one second, turn the tester switch OFF.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Minimum acceptable megger reading = (generator rated volts / 1000) + 1 megohms; 500 V megger; do not apply voltage longer than one (1) second.
- Rotor minimum insulation resistance: 1.5 megohms.
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.