I'm installing a 240V outlet in my shop to run a welder and I'm trying to understand when a neutral is needed and when it's not. The welder has a NEMA 6-50P plug, so I don't need to run a neutral line, right? That said, there are plenty of 240V receptacles/plugs that have 4 holes/prongs. I presume these are for L1-L2-N-Gnd. Is this because whatever is being plugged in here has some 120V components?
Here is part of my confusion: my dryer can be wired in either a 3-wire and 4-wire configuration. If the dryer has 120V components (I suspect all of the control hardware runs on 120V and the only things powered by 240V is the heating elements) then what is the return path since there is no neutral? Does current return through the ground in this configuration (seems bad)?
Regardless of whether a neutral is needed or not, I plan on running the neutral to my new outlet just in case I ever need it (bad idea?). FWIW I'm in the US.