Sub panel separate garage

Question

I'm currently building a small wood shop in my 2 car garage and need some assistance in what size of copper electrical wire to use.

• Garage is 60ft (20M) from house, estimate 80ft (25M) of wire
• Have underground PVC conduit is 1 1/4" inside diameter
• Currently have table saw (15amp), drill press, mitre saw and other small equipment.  Future installations, saw dust collection and shop heater -hoping 120v, not 240v.  The shop will be about 290sq ft.
• Aiming for 60 amp service
• located in Northern Ontario Canada

Unable to find 6/3 copper wire due to demand.  Can I run 2 separate 10/3 wires, each having their own 30 amp breaker on the main panel and connecting them together to the sub panel in the garage. I'm hoping the 2x#10 wires will fit into the PVC pipe. Figured 2x#8 would be too big.

Thank you,

Bruce

Answer 1

You've got conduit. Use it properly. That means individual wires instead of cables. Plus, use aluminum instead of copper and save a lot of money.

Using Home Depot prices (which are not necessarily the best, but a good easy way to compare):

• 6/3 copper = unavailable, and about $8 per foot
• 10/3 copper = only good for 30A = about $1.67 per foot
• 6 AWG copper = single wires, so x 3 = $0.83 x 3 = $2.49 + 10 AWG ground = $0.32 = $2.92 per foot
• 2 AWG aluminum = single wires, so x 3 = $0.52 x 3 = $1.56 + 4 AWG ground = I'm having trouble finding that, so throw in a 2 AWG = $0.52 = $2.04 per foot and it is good for 90A.

You can't run 2 x 10/3 copper, but you wouldn't want to anyway as it costs a lot more than 2 AWG aluminum. And the individual aluminum wires will be a lot easier to pull than any cables. According to the Southwire Conduit Fill Calculator, 4 x 2 AWG aluminum will fit just fine in 1-1/4" schedule 80 PVC.

Your actual pricing will vary, but unless you happen to stumble across some copper wire of questionable provenance, it is extremely unlikely that you will find copper that can beat aluminum pricing, at least not for a while.

There are issues with aluminum at smaller sizes, but it is standard for panel/subpanel feeds.

Answer 2

Allow me to add my voice to the chorus of people recommending #2 aluminum wire, and individual wires if the conduit run is complete end-to-end. (if it isn't, complete it).

I would avoid copper. The lugs on the subpanel will be aluminum because essentially all large lugs are (as well as neutral and ground buses). You don't want to deal with dissimilar metals.

Copper is not more deluxe, it's actually kind of a bad choice for feeder for above reasons.

Some people worry about aluminum because of stuff that happened in the 70s on small 15-20A branch circuits. That is poorly understood by the public, but in fact was not aluminum's fault; rather some comically bad misapplication of non-AL-rated receptacles, and failure to set torque to spec. Wrong torque continues to make problems for copper wire and torque drivers are now a Code requirement.

Aluminum has proven perfectly safe at these large sizes, and #2 is designed for 100A services but it can also be used for feeders up to 90A. The 60A breaker will accommodate #2 wire. It's very popular so it's unlikely to be out of stock.

#6 aluminum may also be available, that is good to 50A (so 2 banks of 50A each).

Assuming your conduit is continuous end to end, the cable types you can use are

• MH feeder for a cable with all conductors included in it
• THWN individual wires
• XHHW individual wires
• USE/RHW individual wires
• Cannot use SER or SEU as it is not rated for outdoors in conduit.

Make sure you are calling ALL stores in your area, not just Home Depot and Lowes. Include local family-owned lumber yards and electrical supply houses.

NM-B cable is not allowed outdoors, not even in conduit. UF cable is very flat and wide, and #6/3 UF requires 2" conduit as a result. All of these are hideously expensive compared to aluminum #2.

Paralleling two sets of copper wires is illegal. It requires the source end to be UL listed equipment specifically rated for paralleling.

Answer 3

Not sure about Canadian codes, but in the US you can't run parallel feeds of a wire size of 1/0 CU or AL. I would strongly suggest AL wire rather than CU due to the cost difference, if allowed in your jurisdiction. Also, run everything you can at 240v. Less voltage drop, can use smaller wires. I have a decent sized wood shop and run my table saw, band saw, jointer, planer, compressor and dust collector all at 240v. If you go with 240, you'll need to provide the appropriately configured outlets and have to make a small change to the wiring on the motors (instructions/diagrams are usually attached), assuming they can accommodate 240.