Can I change an outlet circuit to 240V (NEMA 6)?

Question

I'm in an American house sitting in a jurisdiction that applies NEC 2014 unaltered. I've got a home office room with all the outlets on one 20A circuit. It is legal to 2014 code in all respects.

Who cares why, maybe I collect European pinball machines, maybe I just need a lot more power in the room, between my server grade PC and window air conditioner. I decide I want to convert that outlet circuit to 240V and install all NEMA 6-20 outlets. Pic

It's wired in NM 12/2 but I mark the white wire with red tape at every accessible point. Ground but no neutral. I have the requisite AFCI or GFCI breaker if required (whatever the circuit had before).

What code of Code compliance issues am I going to run into? After all, I do have outlets in all the right places.

Now suppose I also wanted to power a permanently installed light fixture. I want to use one rated for 240V. Any code issues there?

Answer 1

No problem. As long as you install a double pole breaker, make the white wire an ungrounded conductor (including marking as you describe), and change all the receptacles and devices to 240 volt devices.

Answer 2

I see there is no accepted answer yet, so here are my concerns:

NEC 210.6(A) would allow only loads greater than 6 amps (1440 VA) because this "home office" would be part of a "dwelling unit". This rule also seems to disallow the use of 240V luminaires in a dwelling unit.

NEC 210.52 requires 125-volt receptacles for a "Dwelling Unit". If you convert "all the outlets" to 240V then you'd have to add a new circuit for 125-volt to stay in compliance anyway.