Help with wiring my garage.

[lombard]

So, my builder, being an organization of geniuses, gave me exactly one accessible outlet in my garage, good for all of 15 amps. My breaker panel is in my garage, surface mounted in a small frame work that goes up to the ceiling to allow all the housing wire to route through the attic.

I want to add two 20A circuits in my garage, each with 3-4 outlets. I had intended to use schedule 40 PVC conduit to route both circuits through the garage, all surface mounted on the walls. Then I started checking the NEC and got stymied by the regulations regarding routing electrical in conduit, especially romex.

I don't have the option to route everything in-wall since 60% of my garage walls are solid poured concrete. So I need suggestions...

[Tom Slick]

What is your question?

Romex (NMB) in Conduit? Not allowed except under specific exceptions. Run THHN wires in conduit.

[reddog552]

NMB in conduit

NMB is allowed in conduit. Athough I stay away from it.

[lombard]

So basically, the easiest solution is THHN in conduit. That's what I was thinking. I figured an alternative possibility might present itself.

[JR]

Metal Clad (MC) is also a code-compliant option for surface mounting. It's not as pretty as conduit, but it's easy to use.

JR

[Tom Slick]

THHN is much easier to pull through conduit and is less expensive. There really isn't any reason to pull NMB for normal wiring.

[reddog552]

Sch. 40 pvc

SCH 40 is not allowed for phisical Damage reasons.PVC Sch.80 is identified for areas were phisical damage may occur.

[woodturner]

I want to add two 20A circuits in my garage, each with 3-4 outlets. I had intended to use schedule 40 PVC conduit to route both circuits through the garage, all surface mounted on the walls. Then I started checking the NEC and got stymied by the regulations regarding routing electrical in conduit, especially romex.

I assume you have open joists/rafters? I would surface mount 1/2" EMT (metal conduit) to metal boxes on the wall. The conduit only needs to extend to the rafters. Run NM-B in the conduit to the boxes, then across the rafters to the panel. I'd use 10 guage NM-B and 20 A breakers and receptacles.

[lombard]

Well, I don't have open rafters. It's a finished ceiling.

Guess I'm back to conduit and THHN. Just to be safe, I guess I'll bump up to schedule 80.

Couple more questions, since I don't have time to run to the library to get a copy of the NEC. Like I said, planning to run two circuits, 20A each. That pushes me to 12ga wire. Total of four current conductors. What's the smallest diameter conduit I can run? 3/4"?

Any particular requirements when it comes to the colors used for the THHN insulation?

Aside from easier bending/pulling, any particular reason to choose between solid core and stranded?

Finally, can I get by with running one ground wire for both circuits?

Thanks in advance guys.

[cabinetman]

I would suggest getting advice or service from a qualified electrician. Advice from forum members could be right or wrong, and they hold no responsibility for electrocution, fires, or tool damage.

.

[woodturner]

Like I said, planning to run two circuits, 20A each. That pushes me to 12ga wire.

I would consider using 10 gauge wire. The startup inrush current for motors can be two or three times the rated current, and the larger wire will have less voltage drop. Basically, for a small additional cost, your motors will run better and cooler.

Any particular requirements when it comes to the colors used for the THHN insulation?[

Standard color code - black or red for hot, white for neutral, green for ground. There are some other colors allowed, but those are the basics.

Aside from easier bending/pulling, any particular reason to choose between solid core and stranded?

Solid wire can be a little easier to terminate, but probably doesn't matter much in this application.

Finally, can I get by with running one ground wire for both circuits?

Technically, that would not comply with NEC. There are specific circumstances where that is allowed, but this application doesn't appear to meet them.

More importantly, it is less safe. Wires can behave in non-intuitive ways when subjected to ground faults. If a common ground wire is used, in some circumstances the ground is not as effective.

[Mr__Bill]

Aside from easier bending/pulling, any particular reason to choose between solid core and stranded?

As I recall, in some jurisdictions with stranded wire you must use crimp on connectors to attach to the devices or splice a short piece of solid wire to make the connection, and crimp connectors rather than simple wire nuts at the splices.

Stranded is much easier to pull but....
If you unspool the wire rather than just pulling it out like a slinky, and not let it get twisted and make sure there are no kinks in the wire the solid wire will pull in rather well.

If you go to #10 solid wire you may need larger or deeper boxes and will need larger wire nuts for the connections. You also may wish to put in two duplex receptacles at each location. If you group your tools it's easier to leave them plugged in rather than having to switch the plugs.

Bill
only two things have kept me from becoming rich and famous.

Oh, and... I'm not an electrician, the above is a product of my experience, free advice should be judged by what you paid for it.

[jdon]

... since I don't have time to run to the library to get a copy of the NEC.

The great advice on this forum notwithstanding, it might be worthwhile to take a little more time to research. Personally, I find it hard to dig the specific nuggets I need directly out of the NEC.

For decades, my go-to source had been H.P. Richter's "Practical Wiring" (the most appropriately titled book ever). It hews to the NEC, but in a much more accessible- and yes, practical- style.

[lombard]

Thanks for all the advice guys. I've got to do a few calculations to determine the acceptable conduit size for this job. I'm also going to have to track down a cheaper supplier of THHN than the local borg. I'm not talking about any really long runs, so 4 500 ft spools (one black, one red, one white, one green) is going to be overkill, both on the amount of wire and the price. My local HD and Lowes both seem to only carry these 500' spools.

10 ga wire would certainly be nice, if only to allow for any necessary downgrading of the amperage rating that seems to be necessary at times for running in conduit.

I've been putting this job off for a while and really wanted to just jump on it. Guess it won't be happening any time soon.

[BobSch]

My local HD and Lowes both seem to only carry these 500' spools.

Check with a local hardware store. Around here, at least, some of them still sell by the foot.