I think it may also depend on duration of the welding your doing.
I lived in a rent house that had the washer and dryer across from each other as you passed from the kitchen into the single car garage. The dryer had a 30 amp circuit and the breaker box was halfway across the house (only about 1100sf house) in a bedroom closet. I surface mounted a dryer outlet up on the wall on a 1x4 I attached to the wall and used a dryer plug to wire to the back of the outlet and plugged it into the normal dryer outlet. I plugged the dryer into this outlet. On the opposite side of the wall, I put another 30 amp outlet on a 1x4 and ran some heavy 4 insulated wire 'romex' thru the wall to the other outlet and hard wired it to the inside outlet, so this plug was hot if the inside plug was plugged into the normal house outlet. I hard wired my 6hp direct drive 60 gallon Sears upright compressor to the outside outlet and plugged in a Lincoln AC cracker box (100amp?)stick welder. When I wasn't in the garage, the compressor switch was turned off and the ball valve to the distribution system (1/2" pvc pipe on one wall with and outlet at the front of the garage and one at the rear with a drip leg, and combo dryer/regulator connected tot he compressor with a 3' long flex hose). If I went into the garage and was working, I'd unplug the dryer to let the wife know I was using my equipment outside. I never ran the compressor at the same time as the welder and I doubt I ever made a pass longer than about 8" with a 6013 1/8" rod. I think I only tripped the breaker once when I forgot to shut the ball valve and didn't turn the compressor off. The wife was running the dryer and the compressor fell below the what the PSI switch was set to and the compressor kicked on and flipped the breaker.
