Generac GT-990 — Rotor Insulation Resistance Test
Testing & diagnosis
For the Generac GT-990, from the Generac service manual.
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Before you start
- Disconnect and isolate all leads before testing.
Procedure
- Remove brush holder completely.
- Attach all stator winding leads to ground.
- Connect red tester lead to positive (+) slip ring nearest rotor bearing.
- Connect black tester probe to clean frame ground on rotor shaft.
- Set tester to 1500 volts and apply for one second only.
- Observe breakdown lamp.
- If lamp comes on, clean and dry rotor and repeat test.
- If breakdown lamp comes on during second test, replace rotor assembly.
Tools required
- Hi-Pot tester Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Rotor minimum insulation resistance 1.5 megohms
- Do not exceed 500 volts for megger test
- Do not apply voltage longer than 1 second
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.