I could get more power to my shed from my existing panel if I really wanted to, but the problem is you cant buy single phase welders that draw more than 15A @ 240V.
In order to go bigger, I need to go 3 phase, if for no other reason than, I can't get the equipment.
Although, I have heard stories about running 3 phase welders on a single phase, because in reality they are actually a single phase unit, but are wired to a 3 phase plug because they need the current supply available from a 3 phase outlet.
Cheers
Rohan
Huh? Maybe I'm losing something here... The Lincoln "Tombstone" and similar Hobart/Miller welders are 220V, "single phase" welders, needing 50 amp (or thereabouts) supply (although many people have said they have successfully used a 30 amp clothes drier circuit).
Welders that are rated 3 phase are not merely a single phase unit hooked up to two legs of a 3 phase circuit (well, maybe there are some welders of dubious origin that might be made that way). They use all 3 phases, with a transformer made specifically for that, resulting in decreased power usage and longer duty cycles.
There may be some confusion here because a 220 volt circuit, though often called single phase, is really a 2-phase circuit. Each phase is 180 degrees out from the other. There's an intermediate neutral; taking either leg with respect to neutral yields 110 volts. So there's 3 wires--one hot leg, the other hot leg which is 180 degrees out of phase with the first, and the neutral. There may also be a ground wire but it's not needed for actual operation of the machine.
3 phase power has 3 wires, but they are all hot, and each leg is 120 degrees out of phase with the others. There may of course also be a 4th ground but again that isn't needed for the operation of the machine. Pulling significant loads from just two wires (of a 3 phase supply) creates an imbalance which can harm the supply transformer.
Oh, here in the US at least, it's not easy for residential customers to get 3 phase power from the power company (too much hassle for the power company to set it up for the low demands of a typical homeowner). Most folks that want 3 phase run a converter to generate the 3 phase themselves.