Cummins/Onan — Changing Three-Phase AT to Single-Phase
Repair & overhaul · Transfer switch
From a Cummins/Onan service manual — check it applies to your exact model before use.
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Before you start
- Failure to remove AC power from the automatic transfer switch and to disable the generator set presents a serious shock hazard during this modification.
- Incorrect voltage may damage transfer switch.
Procedure
- Open the cabinet door of the automatic transfer switch.
- Move the operation selector switch to STOP.
- Disconnect the battery cables of the starting batteries.
- Remove the AC line voltage from the automatic transfer switch.
- Remove the control disconnect plug and open the control accessory panel.
- 400 ampere AT only: remove one screw from inside center support for the left cabinet door and open.
- Remove generator, line and load connections from the transfer switch terminal C.
- Connect single-phase generator, line, and load connections to respective terminals A and B.
- Control accessory groups 10-15 and 20-25: remove undervoltage sensors 2 and 3 (if equipped) and insert 300-0927 bypass plug modules into openings 2 and 3.
- Control accessory groups 51 through 55: replace the panel with one matching the single-phase voltage.
- Remove one screw on top and one screw on bottom from inside the meter-lamp panel flange.
- Swing meter-lamp panel outward and rewire transformers T11 and T12 as needed.
- Close the meter-lamp panel and secure the top and bottom with two screws.
- Close the control accessory panel and reconnect the control panel disconnect plug.
- Restore AC line voltage, reconnect starting batteries, move selector switch to RMT or NORMAL, close cabinet door.
Source: Cummins/Onan 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.