text: why 120 volt ac current in us and canada? europe has 240 v ac current as basic electrical supply.  1- why us and canada has only 120 v ac.  2- along the street on the poles there are only three wires - where is the fourth zero wire. are the generators wired differently? - european lines have fourth zero cable - 240 v you get between one phase and zero. what is the difference here? good question!  because copper was so cheap in the u.s., it was not a big deal to use larger wires that are needed to carry the larger amperes of household circuits.  remember volt x amp = watt, so in order to carry a large watt appliance, you need more amps, (double the amount you need in european and other cities) and in order to carry larger amp amounts you need bigger wire.  all appliances in the u.s. are maximum about 1600 watts, which when you plug into a 110-120 volt, gives about a 15 amp circuit.  it is too bad though, for in england for example, an ordinary tea kettle (electric of course) heats so much faster because it is about 3000 watts of heat! not sure what you're asking in #2