I've got an old dryer outlet in a 1 gang box with 10/3 Romex cable running to a 2-pole 30amp circuit breaker. I've converted the old laundry room into a server room. I want to get a bigger UPS that requires an L5-30R outlet. Since there is already 10/3 Romex run I have a few options.
1) Install an L14-30R and use a Y-adapter that breaks the two poles into two L5-30R outlets.
2) Install two L5-30R outlets, pigtailing the neutrals and grounds and split the two hot legs from the 10/3. This requires a new box and extra work but might be worth it long term.
3) Something smarter?