FWIW, the H405-E power distribution box (the one with the tee handle) on a
VAX 6310, and perhaps others, uses the C phase (aka L3, aka the brown
wire, aka the black wire with a white stripe, depending on where you see
it at!) to operate the logic that turns on the contactor that actually turns
on the machine.  At least, on mine it does.

What this means is those of you who are eliminating one of the legs of the
three phase supply (like myself) will need to make sure that it remains
connected.  Those of you who are bridging two legs together should be
fine.