Electrical sub-panel question

[rbstern]

I've been doing my welding in a detached garage, which has a 120v/20A circuit serving the garage door opener and a couple of recepticles, along with another circuit that is 15A for the lighting (the tail end of a circuit serving lighing in the nearby laundry room). I'm hitting the limits of my 120v equipment and want to advance to a 240v welder, probably arc.

Stupidly, in this relatively new construction (2018), I didn't anticipate heavier welding in the garage, and didn't have the electrician run a dedicated 240v circuit. And doubling down on stupid, I finished much of the basement recently, cutting off the easiest path to getting wire from the main panel to the garage. So I made this task harder for myself.

Staring at most of a 250' roll of 12/2 left over from wiring the basement, I thought I would just try to snake it through to the garage (the buildings are attached by a breezeway roof, which houses the wiring between the structures) and run a dedicated 240v/20A outlet just for welding. That would probably handle 98% of what I need, and for the heaviest welding, I could move whatever portable 240v welder I get down to the basement workshop, where 240/30A or even 40A are easily implemented.

But then I started thinking about other tools I might be running in the garage, in the future: Plasma cutter, compressor, metal bandsaw. Heavier sanding equipment. I now realize, if I pull anything, it probably should be at least an 8/3, maybe a 6/3, feeding a 40A or 50A sub-panel, freeing myself from the limits of the dedicated circuits.

Just wanted to confirm with those who are more electrically aware than I: For a sub-panel, I need two hots, neutral and ground for the sub panel. The ground is grounded to the main panel ground. The neutral is bonded to the main panel neutral. The hots...each to the 120v leg of the main panel on a double pole breaker. And, the sub-panel needs a separate ground wire, to it's own ground rod. Do I have that right?

Anything else to consider?

Side note: Plenty of physical and theoretical capacity in the main (200A) breaker box.

 

[Diggin It]

6/3's gonna be a bugger to pull any distance. How far are you talking about from the main panel and meter base?

 

[BrokenTrack]

I recently did what you are suggesting, but I went with 2-2-4 (bare neutral), but went OVERHEAD. I put a electric pole in halfway because we get ice storms here and i wanted a little less strain on the wires.

I had an underground wire, but snagged it with my bulldozer, so this time I went overhead.

My run was about 100 feet.

 

[rbstern]

6/3's gonna be a bugger to pull any distance. How far are you talking about from the main panel and meter base?

Maybe 70', and it's going to be a bit of a maze. First 30' is easy, through the open truss basement ceiling. Then it gets hard. Got to get up to the attic via a great room wall; not sure it can be done without sheet rock surgery to create new holes through the 2x6 plates. Hence, why I am kicking myself: Eight months ago (pre-basement sheet-rock), this would have been a one hour, two beer project.

 

[rbstern]

I recently did what you are suggesting, but I went with 2-2-4 (bare neutral), but went OVERHEAD. I put a electric pole in halfway because we get ice storms here and i wanted a little less strain on the wires.

I had an underground wire, but snagged it with my bulldozer, so this time I went overhead.

My run was about 100 feet.

Love it, but that would be a particularly expensive project for me. Not so much the wiring, but the ensuing divorce for putting overhead power pole anywhere near my wife's carefully tended gardens.

 

[rbstern]

Rob, so I understand correctly: Assuming 40 amps, I would have to pull an 8/2 (or 8/3), and the grounding and neutral wires could not be in the same Romex assembly?

 

[tshep]

It's my understanding (Va Mst Ele) that a simple, single service connects ground and neutral at only a single point - a tie or screw in the main panel, and stay separate from there out.

 

[crazyal]

If you are doing a sub-panel then it needs a separate neutral and ground wire. The sub panel box can't have the neutral and ground tied together.

When I was much younger and still living in my father's house I had the exact same problem. Not wanting to deal with spending a lot of money what I did was buried plastic conduit. I had to go under a sidewalk so I dug a hole on each side and pushed a piece of pipe through the dirt. His basement was cement wall and I wanted to do it just once so I drilled 1/4" holes in a circle and then broke the center out. After sliding the conduit into it I put grout around the hole. The garage had a block wall so it was easier but basically did the same thing. I ran 2" conduit so I had extra room for a phone line. I ran a 30a 120v line and a 30a 240v line vs running a line for a sub panel. Plus I had the existing 20a 120v line. Running 10 gauge wire is much easier than larger stuff.

When I built my house I had to run 350 mcm, which is larger than 0000, aluminum wire. What I did was slid each section of conduit onto the wire vs trying to slide it through after laying the conduit. It's also how I did it when I ran power to my garage's sub panel. In Georgia you probably don't have to worry about frost and an expansion joint.

 

[3Ts]

You should consider putting 240v/50 amp service in the garage/shop. A lot of welders have a 50 amp plug - not that they actually use all 50 amps (I've run one off a dryer outlet with the proper plugs and sockets on a short power cord). That way you can run it at full capacity if you ever need to.

 

[LS Tractor Owner]

Technically, if I am correct, by NEC code, sub panel boxes rely on the ground and neutral from the original supply box. No additional ground Rod needed for the sub. This may have changed since I last checked over a year ago. Someone with more knowledge will be along shortly to confirm or correct me