Brad,
Most of those machines are 3-phase. So I have a rotary phase converter making 240 single phase into 240 3-phase. Those 2-gang outlets have a separate 3-phase, 20 amp, 240 volt recepticle and a 120 Volt 20 amp recepticle.

NEMA_L21-20_Hubbell.jpg

1993 Daytona, 5.50 at 130mph (1/8) 1.19 sixty ft (PG). Link to 572 B1 - Part 1