Retrofit in an Older Garage

[bad_idea]

Friend of mine bought a house from the 70s with a garage out back. The garage has a single 120v circuit running out to it feeding a couple outlets and an overhead light. The circuit is fed from the main panel in the house through conduit out to the garage (likely 3/4" conduit, but not sure the size). He's not the garage dwelling type, like most of us here, just an average joe looking to make a useable space. He would like to get a welding machine and do some basic auto repair out there.

What is the maximum circuit size he can run through the existing conduit (lets assume 3/4" PVC for now). What is the minimum requirements for a sub panel out there? I assume he will need to drive in some ground rods? How many circuits can you have before you need a main disconnect?

Again, looking to make the best of what he's got. Not looking to dump a fortune into the project.

 

[pattenp]

If 3/4" should be able to pull three #6Cu thhn/thwn and one #10Cu thhn/thwn for 60A. Using a 100A main disconnect panel for the sub is the best option.
Two ground rods should be used.
Over six disconnects requires a main disconnect.

 

[Bert_]

In my area I would be VERY surprised if it was in conduit the whole way. I would expect UF direct buried.

 

[Syberia]

3/4" PVC is good for 4 #6. 60 amps.