So to this point I've read just about everything on 240v, 3 prong wiring and I'm still stuck.
I bought a 240v, 4800w 20amp garage heater. I added the 30amp circuit (noted on the box as the required circuit), ran the 10/2 wire (it happens to be 10 CU 2, if that makes a difference, I was told it didn't), connected the 6-30p outlet, tested L1-ground, and L2-ground, each at 120v and... the heater doesn't work.
I'm sure I'm missing something tremendously simple, but it's completely evading me.