Hi folks, first time posting here but I've spent the past week scouring articles here and have learned quite a lot. Great stuff.

I have yet another detached garage project. The house was built in 2009 and currently the wiring looks like this (from a side view)


I'd like to put some woodworking tools out there (contractor saw, miter saw, router table, all listed @15A or less) and run them one-at-a time along with an 11A shop vacuum for dust collection. Thus I need to upgrade the capacity. In an ideal world, I'd follow "Plan A" and replace the underground line with a 60A (or more) feeder (THHN inside schedule 40 conduit), add a new panel and grounding rods at the garage, reconnect the existing circuit, and add new 20A GFCI receptacles on dedicated circuits for the tools and vacuum.

One difficulty however is that I'd need to run new conduit under the concrete slab patio, since the current conduit is only 1/2" diameter. Tearing up the concrete is simply not an option. There's also not much room on either side of the slab to work, so tunneling under would be challenging. I might be able to route conduit the long way around but this is also a lot of work.

In any case, I would be remiss if I didn't at least enumerate all my alternative options. If for no other reason than to rationalize Plan A with my wife

I have a few alternatives in mind that do not involve running new conduit. I would sincerely appreciate your thoughts about their safety/legality/practicality.

Plan B:

From what I understand, the latest NEC guidelines say that 2 circuits in a detached structure must be fed by at least 30A capacity feeder. (More than 2 circuits require 60A feeder IIRC.) What I'm confused on is the multi-wire topic and whether this configuration constitutes 2 circuits or 4.

Plan C:

This one clearly has much less capacity. Question again regarding multi-wiring and whether this constitutes a single circuit (and thus no need for a sub panel and grounding rod).

Also, is it ok to add the second hot using just a single THWN conductor, or would I be required to remove the builder's UF cable and run four new THWN conductors?

Plan D:

This is essentially no plan at all, and what I currently resort to. I'd just add a dedicated circuit for convenience and to ensure each tool has its own circuit.

 

It is amazing they even were able to pull UF in ½" conduit. the first challenge would be getting it out. Four #10 will fit in ½" conduit so you could run a 30amp feed to a subpanel if that will meet your need. However are you sure the conduit isn't just used to sleeve the UF where it enters and leaves the ground? (Given the near impossibility of pulling UF in ½" conduit I'd guess the conduit isn't continuous.)

Plan B: All current carrying conductors must be in the same raceway so not code compliant.Wrong, you can have only one circuit. A multiwire circuit is considered a single circuit.

Plan D: Extension cords are for temporary use only.

My suggestion if the garage and house door line up is to build an open breezeway between the two and run your wiring there. If not just run a trellis between the house and garage and use it to conceal an overhead conduit.

 

Thanks for the speedy reply!

Excellent question. During landscaping (deep tilling) I discovered that the conduit does indeed run horizontally after both sweeps. I couldn't verify underneath the concrete obviously though. Keep in mind that it's 14-2 UF in two sweeps for about 26 feet. In any case all this is moot if it's not enclosed under the concrete.

Thanks greatly for the code check. I think I understand what you're saying regarding multi-wire. I'll try to dig up the reference that led me astray.

Is Plan C thus non-compliant as well? Is this considered two circuits because the two loads (existing devices on one phase, new receptacle on other phase) are not sharing a common 14/3 NM-B, but rather are on two separate 14/2 NM-B "raceways"?

Thanks again.

 

Ray, you are a lifesaver

I decided to test my assumption about the conduit. I ran a fish tape down one side. 13 feet in and it stopped. As I reeled it back in, I noticed water on the tape. Not looking good. Then I ran fish tape down the other side. Stopped at 7 feet. This time I found clay at the tip of the tape. So that confirms it... there's about 6 feet of wire beneath the slab that isn't enclosed in conduit

Plan A it is.... Now to mentally prepare for the much bigger job ahead. I guess I'll be running extension cords from the house in the short term, and storing them away when not in use.

Edit:
Great idea, never even occurred to me. Probably more effort than it's worth in my particular house, but good food for thought nonetheless.