- What size conduit should I use? (I was thinking 3/4")
Since you're pulling more than 2 wires through the conduit, you're only going to be able to fill the conduit to 40%. Since you didn't specifically mention what type of conduit you're using, I'll list all metallic and PVC conduit.
- 3/4" Intermediate Metal Conduit (IMC) @40% = 0.235 in.²
- 3/4" Rigid Metal Conduit (RMC) @40% = 0.220 in.²
- 3/4" Schedule 80 PVC @40% = 0.164 in.²
- 3/4" Schedule 40 PVC @40% = 0.203 in.²
I'll assume you're using THHN/THWN/THWN-2 conductors, so you'll need to know the area of these conductors in the various sizes.
- 12 AWG = 0.0133 in.²
- 8 AWG = 0.0366 in.²
To figure out if the conductors will fit, you just have to add them up.
3 #8 x 0.0366 in.² = 0.1098 in²
3 #12 x 0.0133 in.² = 0.0399 in.²
0.1098 in.² + 0.0399 in.² = 0.1497 in.²
You end up with a conductor fill value of 0.1497 in.², which means you'll be able to use 3/4" conduit no matter what type you choose.
NOTES: For a look at some of the tables where these numbers came from, see this answer.
- Can I snake all wires for the AC and outlet in one conduit (2 conductor 1 ground for ac [8awg] / 1 conductor 1 neutral 1 ground for outlet [12awg]) - not sure the fill on this size
No problem, see above.
- When I stub up, I need to wrap around the foundation a little bit; any issue going above a hose spigot?
Shouldn't be a problem.
- Am I crazy for using rigid metal conduit? A lot of people I know say just go 'as deep as I can' and use PVC. But that's against code and even though this won't be inspected I try to stick to code as much as possible
You can use metallic conduit if you want, but it will likely be cheaper to use PVC (even though you'll have to dig deeper).
I think you may be confusing PVC pipe (used for plumbing), and PVC conduit (used for electrical). There's no problem at all with using PVC conduit, unless there's a local amendment that restricts its use. However, you'll only have to bury metallic conduit 6" deep, whereas PVC will have to be 18" deep. So if you don't like digging, metallic conduit might be worth the extra cost.
The first problem can be dealt with using a Bell 5403 or equivalent weatherproof extension box to provide a place to hook the conduit to and some extra cubic inches for the additional wire fill. You'll need to hook a ground pigtail to it, by the way -- there do not seem to be non-metallic weatherproof extension boxes.
Since you are running conduit under the deck -- you can run individual THWN wires inside it instead of a UF cable (although running UF aboveground is permitted when protected from physical damage and direct sunlight if it isn't IDed as sunlight resistant), and running THWN will make it easier to pull even with an oversized conduit -- 3/4" inch will provide ample space for a single circuit extension like yours. Don't forget to put in expansion fittings, lest your conduit run do the snake on you!
Last but not least -- simply use an ordinary outlet for the new outlet, and run it from the LOAD terminals on the existing GFCI. (Although putting two GFCIs in series won't break anything, it could confuse you as there is no guarantee as to which one will trip when something happens.)
Best Answer
Sure. What you're talking about is similar to the "Electrician's Outlet"... an outlet right next to the panel which is fed by a dedicated breaker. So the electrician can plug in portable lights etc. when the rest of the house is turned off for maintenance. That's pretty much standard practice for interior panels.
The electrician's outlet just uses a conduit "nipple" (prefab short pipe) that gives you an inch or so of length, so you get far enough away from the panel so the covers don't jam.
One common trick I see is using an offset nipple, which is about 2" long and has a small zig-zag. The offset isn't used for anything, it's just a handy, pre-made 2" nipple lol.
But if you want to run conduit a little farther and make it 3' away, that is fine. I recommend planning on water getting into the pipe, and exiting the bottom of the panel in a "drip loop" sort of deal.
Any outdoor recep is going to need an outdoor in-use cover.
You cannot use Romex (actually NM-B) in conduit because Romex (NM-B) is not rated for outdoor use. Also, there's a size issue: you must treat any cable as a single round wire of the large diameter (because it twists), and that makes it too big for many conduits. UF cable is allowed outdoors, but it's even thinner and wider than NM-B, and that makes it require HUGE conduit!
I'm not really sure what people's hangups are with THHN, it's really, really wonderful stuff, especially stranded. You'll never want to alligator-wrestle Romex again! The only snag with stranded is it's hard to hook over screws, but GFCI receps have screw-to-clamp terminals, and that makes it easy.
If you run #12 wire you are welcome to use either a 15A or 20A breaker as long as it's a dual 15A recep. (a 20A recep is also acceptable on a 20A breaker).
All the THHN I own is 12 AWG (except for the larger stuff obviously). I don't see any reason to own it any #14. #12 works for #14 and now I only have to stock one thing.