Generac — Generator Voltage Checks
Testing & diagnosis · Generator supply to transfer switch
From a Generac service manual covering: RTSC400A3, RTSW300A3, RTSW400A3. Check it applies to your exact model before use.
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Before you start
- Do NOT proceed until generator AC output voltage and frequency are correct and within stated limits.
Procedure
- On the generator panel, select MANUAL mode. The generator will crank and start.
- Allow generator to stabilize and warm up at no-load for at least five minutes.
- Set generator main circuit breaker (CB1) to ON (CLOSED).
- With an accurate AC voltmeter and frequency meter, check the no-load voltage and frequency.
- Measure across ATS terminal lugs E1 to E2; E1 to NEUTRAL and E2 to NEUTRAL.
- When voltage is correct, turn OFF generator supply to the transfer switch.
- Set generator main circuit breaker (CB1) to OFF (OPEN).
- On the generator panel, select OFF to shut down the generator.
Tools required
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Terminals E1 to E2: 240-246 VAC
- Terminals E1 to NEUTRAL: 120-123 VAC
- Terminals E2 to NEUTRAL: 120-123 VAC
- Frequency: 60-62 Hz
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.