P=E x I that is, power = the voltage times the current. the maximum current a 120V outlet can carry is 20 amps, so, the maximum wattage is 2400 watts. so, I=P/E which is the power divided by the voltage= the current, so, 2400 watts/30 volts(arc voltage) =80 amps.. so.. 200 amp welders use 240 Volts at 66.6 amps to get a capability of 200 amps.. that's 80 volts x 200 amps=16,000 watts needed.. 16,000 watts/240 volts=66.6 amps on the line cord.. under an established arc, you do get less than 80 volts at the electrode though..