Electrical - running power outside under deck. WWYD?

I was going to put in an exterior receptacle, but plans changed. I now want to run power from this box to a greenhouse. There is a deck running from just below the box all the way to the side of the greenhouse, with a 12 inch gap between the Deck and the GH. I've searched Google, and let me tell you, there are so many opinions I'm not sure of the correct way to do it. The line is 20 amp 12/3 and protected by a GFCI receptacle in the garage (I'll add one in the GH as well). What would you do to get power into the GH?

 

I would run the wire through a conduit from the garage to the gh. That should protect the wire fro weather and critters.

 

How long is the run is first question?

Judging from first pic it doesnt look like there would be a significant drop in current. I really dont remember all the math about it, but doesnt look like a real concern at all in this situation.

You can run UF and bury it deep enough to not be disturbed and likely have it work for the rest of your life.

As stated above, conduit would be the best option for the longest lasting time and least susceptible to damage.

Edit: Most likely points of failure are taps/ improper boxes, so do that shit right.

 

Also keep in mind what all is on the garage circuit. You likely/ hopefully have door openers on their own circuits, and all/any receptacles in the garage on their own circuit. So anything pugged into the garage circuit plays a role i.e. fridges etc.

 

What kind of wire (THW, THWN or UF), and what conduit (pvc, metal or...?). So many options and opinions out there...

It's about 25 feet. Not worried about voltage drop - it's only going to run a small vent fan during summer days and sometimes LED string lights at night. I was hoping to not bury anything since it's under the deck and there's opinions out there on the need to use conduit if using THWN under a deck. It's the THWN that is unknown. It's stranded while the existing wire is solid core. So the connection of the two, gauge of the THWN, etc. is a question.

I have 4 separate circuits for the garage, laundry and screen porch - all 20 amp each. This line will be for convenience receptacles only.

 

HA! I got one circuit in the garage for the openers (pretty sure they were added after original construction in mid 70s), outlets, overhead lights, and for some reason the outlet in the (adjacent) interior laundry room.

 

Going with these. Weather proof boxes, UF wire, short bit of pvc conduit for the sections of wire that aren't under the deck.

 

Usually you want to pull the stranded wire through conduit. Honestly Id just go with the UF. Not sure by the picture how much room under the deck you have? Looks pretty low by the picture, but if you can get under it then just tack the UF up to the joists/boards. You could then junction and pull the stranded through the conduit. Or you could just pull the UF honestly. Not the biggest deal. IF your not going to just bury the UF and use it for the whole run, just make sure the pvc connections are good and that the UF isnt just going in to an open end of pipe. Again, not the biggest deal, but if you're dead set on using the conduit then might as well add the box and fittings to make sure its properly sealed.

 

Also, make as few turns as possible with conduit. Especially if youre pulling the UF through it.

 

There's about 8-10 inches between the bottom of the deck boards and the ground, so i had planned on only using conduit where the UF leaves the box to where it goes under the deck. The long run under the deck will not be in conduit. I'll staple it to the pier posts, not the deck boards themselves. Most deck boards are 8-12 feet long and secured with stainless steel screws, so pulling up a few of them will be easy.

 

Well, sounds like you got a pretty good plan. Have a feeling you do what I do and agonize over planning. Just do it. Get them fans running.

 

Made some progress today. Ran wire under the deck, boxes attached and conduit in place (not glued yet). Need to turn off power to connect but there is a giant pile of laundry being processed that's on that circuit. The deck will be extended to the greenhouse, so most of that will be covered. I'll be able to energize the line tomorrow.