Cummins/Onan — Voltage Regulator Adjustment
Adjustments · Voltage regulator and voltage control rheostat
From a Cummins/Onan owner's manual covering: 230NT2, 230NT4, 250NT3, 275NT6, 275NTA1, 300NTA2, 350NTTA2, NT-855, NTA-855, NTTA-855-G2. Check it applies to your exact model before use.
Applies to: Cummins/Onan 350NTTA2, Cummins/Onan NT-855-G2 engine, Cummins/Onan NT-855-G4 engine, Cummins/Onan NT-855-G3 engine, Cummins/Onan NT-855-G6 engine, Cummins/Onan NTA-855-G1 engine, Cummins/Onan NTA-855-G2 engine, Cummins/Onan NTTA-855-G2 engine
Before you start
- Do not adjust any other voltage regulator potentiometers or rheostats; they are factory-calibrated.
Procedure
- Loosen voltage control rheostat locking nut; turn rheostat fully counterclockwise, fully clockwise, then to mid position.
- Remove cover from voltage regulator housing on engine side of generator conduit box.
- With set operating and voltage monitored, adjust Coarse Voltage Potentiometer to desired generator voltage.
- Perform fine voltage adjustment (+3 percent) with control rheostat and retighten locking nut.
- Stop and restart generator set to confirm proper operation.
- If voltage cannot be brought within range, check wiring per unit wiring diagram and repeat; contact service representative.
- Shut down set and replace voltage regulator housing cover before returning to service.
Tools required
- Screwdriver Amazon
Tool links are Amazon searches (affiliate links); manufacturer special tools may only be available from a dealer.
Specs & values
- Generator voltage adjustable within +/-3 percent of rated nameplate voltage
Full service-parts list: Cummins/Onan 350NTTA2 →
Source: Cummins/Onan owner's 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.