A high-leg-to-ground reading of 265V almost sounds like there may be a misplaced 277V-secondary “power” transformer, with a correct 240V unit for the “lighting” pot.
CharlieE, pardon me, but that’s the idea of having other than a theoretical zero-impedance transformer. Very roughly, the change in voltage on secondary terminals decreases by the per-unit impedance when nameplate loaded versus zero load—e.g., a 3% Z, nominal 240V [or ~247V] transformer terminal voltage drops to about 97% ~233V [or ~240V] when fully loaded.
Equal loading across the ‘open’ terminals [versus across one of the two individual windings] on the open-delta bank approximately doubles. While a 3ø induction motor can succesfully operate with a lower overall [balanced] voltage like a 5% reduction, it will typically experience much greater stator heating if terminal-voltage imbalance is 5% per ANSI/NEMA standard C84.1-1995 Annex D. Discussed at
www.joliet-equipment.com/voltage_unbalance.htm
