The old code from like 30 years ago allowed 10-2 with ground (3wires) and a 3 prong plug. This is still used in older homes.
Both will work fine.
Yes you need another wire. Right now you have 220/240 Volts going to it. That is 2 hot wires. You need a third wire. the Neutral (white) wire. Some not all newer units need that white wire for 120volt for things like lights timers and internal computers/processors.
Technically 4 wires you need. 2 hot, 1 neutral and 1 ground
This is National Electrical Code. You will not pass a inspection to sell your home.
When you "hear everyone saying..." remember that they will not be paying you your fire damaged insurance deductible. You'd be smart to get the advice of an electrician. I'm not an electrician but have had some experience at the level you're at so I'm saying get yourself to the hardware or lumber yard were they sell the right stuff and answer questions like this. BTW, isn't this a car forum?
A 10-2 actually has three wires, two hot, one grd correct? There is only three prongs, but I suspect a fourth wire (10-3) goes to the outlet box itself, there by grounding that. IDK
You need two insulated wires and a ground.
