go by a little 12v adapter at radioshack for twenty or so dollars. that's what i do and it works and even powers a amp and 4 speakers
In North America it takes two "hot" wires to obtain 240 volts.
Don't!
White wire is usually used as a neutral conductor and a 240v ac unit has no neutral. Each leg of the 240 volts is a "hot" leg However, very often a 12/2 or 14/2 NM cable is used to power small window ac units using 240v. In this case one of the conductors is white, but is not a neutral. It is good practice to mark the white wire with black tape so it is readily identified as a hot wire.
Outdoor wire is harder to work with but you can use it indoors.
The dryer is a 240v dryer so two of the wires are your hot wires, or the ones with power on them. One is your ground wire. And the forth is your neutral.
It depends on the amount of power/current drawn from the generator. A small amount of current requires thin wire, more current requires thicker wire. The siae of wire can be calculated when the current is known.
4 wire household wiring is black, red, (hot wires) white (neutral) and bare or green (ground wire). You say 3 wires. Is it 120v or 240v. If its 240v which is more common just use the two hots and the ground and cap off the neutral wire.
I'm sure this isn't what you want to hear, but you probably need to ask an electrician familiar with your service and what you want to connect. As a general answer, you can connect a 240v line to line resistive load like an electric water heater to any 240v source. If you also need the 240v to have 120v line to neutral, like a 240v electric stove that contains a 120v clock and oven light, then its possible if the 3 phase power is connected in a "high delta" configuration, and you connect to the correct leads. If you have a high delta service and want to ignore the 3-phase power service and wire most or all of the loads in the building as a single phase load, the utility may have to be consulted.
5 mm
two hot one ground
16 mm to 18 mm
Shield is ground. White is Neutral, center tap of the transformer from the power company.