Generac — Utility Voltage Checks
Testing & diagnosis · ATS terminals / 3 phase power monitor relay
From a Generac service manual — check it applies to your exact model before use.
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Before you start
- Failure to turn off the UTILITY supply before working on the UTILITY connections of the ATS will result in extremely dangerous and possibly fatal electrical shock.
- The transfer switch is now electrically hot.
Procedure
- Turn ON UTILITY power supply to transfer switch.
- With accurate AC voltmeter measure across ATS lugs N1-N2, N2-N3, N1-N3.
- Measure across ATS lugs N1-N, N2-N, N3-N.
- Locate 3 phase power monitor relay; verify LED green and ON (208 Vac) or NORM indicator green and ON (480 Vac).
- If LED is not ON, rotate adjustment potentiometer counter-clockwise until LED turns ON.
- Verify utility phase rotation matches generator using a phase rotation indicator.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Factory setting 80% of nominal voltage
- 208 Vac system dropout = 166 Vac
- 480 Vac system dropout = 384 Vac
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.