Two common '220V' three-phase systems:

208Y/120V. The windings are connected in a 'wye' or 'star' configuration. Phase-phase voltage is 208V, and any phase-neutral is 120V.

240/120V. The windings are in connected in a 'delta' configuration. One winding (usually A-C) is center-tapped and grounded.

Phase-phase is 240V. A and C to neutral voltages are 120V. B to neutral is EDIT: 208V. This system is also known as 'red-leg', or 'high-leg' since the one phase is a higher voltage to ground.

Either system can accept 3-phase load.

The 208Y/120V can accept 1-phase load on any phase, A, B or C.

The 240/120V system can accept 1-phase load only one phase.

Check for a namplate and wiring diagram on the alternator!

Best Regards,
Jim