If my service disconnect breaker is a 150 and my fuse box isn't maxed out, 3 slots still available would I be pushing the limits to add a 50 amp breaker for a arc welder? I haven't pulled the cover to see what gauge wire is coming into the house or how it's split. I have a newer home (2007) and nothing out of the ordinary requiring power. The typical dryer, stove, water heater and a/c circuit breakers. I don't want to push the capabilities of the fuse box but would really like to add the 50 amp breaker for a 240 lead in the garage.
Depends on how much load the rest of the house is putting on the service at the same time... but if the total demand stays under what your service is rated for, and you use wiring that can handle the 50A demand, you theoretically should be OK.
Run the numbers.
(My electric drier plugs into a 220V outlet fed by a pair of 30A breakers, and I have only 100A total service; that's roughly proportional to what you want to do. When I switch to a gas drier, I'm planning to re-route those 30A legs to my workshop.)