I didn't know 240 didn't use the neutral... I would have thought you'd run 14/3 wire for 240 applications.
It depends on the usage. Nearly all 240v lighting, motors, welders, big window A/C's, etc only require hot + hot to run. Obviously we add a third conductor as an equipment safety ground. This is refered to as 2 pole 3-wire grounding 240 (L1, L2, G)
Very few things need 4-wire 240 (aka 3 pole 4 wire grounding) (L1, L2, N, G). Most notable are dryers and ovens/ranges. In old construction (I believe 1996 this was revised in the NEC) 3 pole 3 wire (NON GROUNDING) dryer outlets (NEMA 10-30R) were no longer allowed, same went for 3 pole 3 wire range outlets (NEMA 10-50R). Dryers use 240v for the heating elements, but 120v for the motor, lighting, timer circuit, etc. Stoves are the same way, 240v for heating elements, 120v for everything else. The real concern is that there is no equipment grounding conductor and your dryer chassis is bonded to neutral. Should the neutral open, you now have 120v of potential on the chassis. Basically, look at your entire dryer as one really big wire that would love to light your *** up, as you are standing on ground and have now become the new current path. To fix the safey issue, 3 pole 4 wire grounding outlets were introduced for ranges and dryers. The chassis is no longer bonded to the neutral, so should the neutral open or a short occur, the chassis no longer has potential.
So, cliff notes;
3 pole 3 wire (L1, L2, N), 120/240v capable, no ground, was commonly used for dryers and ranges
3 pole 3 wire grounding (L1, L2, G) 240v grounded, not capable of 120v, used for lighting, motors, welders, etc as no return current is required. 30A and 50A outlets (NEMA outlets 6-30 and 6-50 respectively)
3 pole 4 wire grounding (L1, L2, N, G) 120/240v grounded, now commonly used for dryers, ovens, etc. I personally install these over 3p/3w grounding for the simple fact that it's a "do all" outlet. If I need 120/240, great, I wire the device with 4 wires. If I need 240v only, also great, only 3 wires are used. This is helpful for example for a volunteer job that I do in which one of our PA systems needs a 50A 4 wire connection, where the welder only needs 3 wire. Again, it's only needed where there are 120v devices that may be present in the equipment that require a return path. These are also commonly used in bigger RV's as again, there are both 120v and 240v devices present in the RV.
