This question raises many others. Are you wiring in an office, a barn, or a house? Is the application to wire a pool pump, sump pump, an air conditioner, an oven, a heater, or what? Where is the appliance located? Is it new or existing? Is it installed and grounded? How far is the application from the main electric panel? Is the wiring to run outdoors or will it be exposed to moisture, extreme temperatures? Will it be run inside a wall or left exposed? What is the amperage rating of the appliance or machinery or heating device? Will this line be dedicated to one appliance or machine? Have you identified the breakers to be used? If so what is the amperage rating? Is the circuit protected? Is your electric supply single phase two wire, three wire, or 3-phase current? In what U.S. State is the intended application? I am sorry. Your question cannot be answered. You see, the fact is if you did not know enough about electrical matters to realize that the question lacked vital detail you should not be doing your own wiring and should hire an electrician for this job. It is too dangerous to do it yourself. This doesn't mean you cannot learn. If you are very interested in obtaining more knowledge you might start with one of the more elementary but thorough paperback books: Wiring Simplified by H.P. Richter if still available. It was published by Park Publishing, Inc., 1999 Shepard Road, St. Paul, MN 55116. Good luck!
In North America it takes two "hot" wires to obtain 240 volts.
The recommended wire size for a 240V electrical circuit is typically 10-gauge wire.
The recommended wire size for a 240V 30 amp circuit is typically 10 gauge wire.
The recommended wire size for a 30 amp 240v circuit is typically 10 gauge wire.
The appropriate wire size for a 240V 30 amp circuit is typically 10 gauge wire.
The recommended wire size for a 240V 50 amp circuit is typically 6 AWG copper wire.
The appropriate wire size for a 240V 50 amp circuit is typically 6 AWG copper wire.
The appropriate wire size for a 50 amp 240v circuit is typically 6 AWG copper wire.
For a 240V steam generator, it is recommended to use a wire with a gauge of 10 AWG for a 30-amp circuit or gauge 8 AWG for a 40-amp circuit. Make sure the wire is rated for the voltage and amperage of the steam generator, and always consult a professional electrician for proper installation.
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.
For a 240V outlet, you should use a fuse that is rated for 240V. The fuse's amperage rating should match the amp rating of the circuit and be appropriate for the connected devices. It's important to use the correct type and rating of fuse to protect the circuit from overloading and electrical hazards.
Don't!