You didn't measure the insulation when you measured did you? I find it real hard to believe, although 4 gauge is commonly used on electric stove plugs...... Just wanted to make sure you knew that you have to measure the copper part of the wire ONLY.
Also, We're talking worst-case here....... That 47.5 amps of draw is only when your welding on the highest output range of the welder..... At lower ranges, your draw is less. You may very well be able to get by on that 30 amp breaker if you're always welding stuff less than 1/2 inch thick.
