I would like to extend a 6/3 NM-B (Non-Metallic) ROMEX Simpull wire diagonally across my yard from basement to a wooden pole that will have the Nema 14-50 outlet. The outlet will be exposed to the elements, since it will not be in a enclosed area.

I have read many opinions around protecting the wire from physical damage, and in some cases that it is prohibited to run the wire in a conduit. Appreciate your help with code that will allow me to stretch the wire diagonally buried under the yard running some 30 ft.

It will be helpful to know the type of conduit I should use, how deep should it be buried underground and how to finally connect the wire to the outlet. the other end of this wire will be directly connected to a electrical panel with 50 AMP breaker. The panel is directly inside the front wall, therefore my plan is to make a hole and pull the wire from outside into the electrical panel.

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  • 1
    Are you open to using individual THHN wires in your conduit, instead of a cable? Dec 6, 2019 at 5:26
  • 2
    Does "diagonal" mean anything special? You are allowed to bee-line at non-square angles compared to buildings or compass directions. It won't mess up the ley lines :) In fact, by putting the wires in the obvious bee-line location, you make life easier for backhoe crews digging up your yard. Dec 6, 2019 at 5:33
  • sorry, I tried to search but did not find what bee-line location means. Can you pls. elaborate? thanks!
    – marc Katz
    Dec 6, 2019 at 12:08
  • 1
    Bee-line means a straight line, the shortest possible route. When bees have collected all the nectar they can carry, they fly straight back to the hive. In fact, you can find feral beehives this way: capture a worker bee, move it, then release it and see which way it flies. Do that twice and see where the lines cross. Dec 6, 2019 at 12:30

2 Answers 2


Cable in conduit

Say what? It's never prohibited to run a wire in a conduit. What's prohibited is running wires in too-darned-small conduit, which is a problem of the cheap. Well, in fairness, it's easy to mis-guess with cable, because a flat cable needs the same space as a round cable of the wide dimension. (because they twist).

For instance, with 1 cable in conduit, the conduit ID must be 138% of the widest dimension of the cable. 6/3UF is flat and 1.223" wide, so the conduit ID must be 1.680". That puts you into 2" conduit.

You need to use UF cable, because the cable you want to use, NM-B, is not rated for outdoor use, and lots of us have experience with NM-B cable failing outdoors.

Why even put cable in conduit?

Because cables are the only kind I have ever heard of. I didn't know there were other kinds of wiring.

Meet THWN-2 wire. It is actual wire, not cable. Like what's inside an NM-B sheath, but with insulation that's up to the task, and wire markings to make it legal to use directly. Needless to say, this packs much nicer into conduit than balky cable, only needing a 3/4" conduit (though I recommend 1" to make the pulling easier).

Also, it's a pleasure to pull, since each wire flexes independently.

Downside: THWN-2 cannot be used outside a conduit. So the entire route must be conduit.

Upside: Shallower burial depth, only 18" cover isntead of 24" for cable. Also, Rigid or IMC metal conduit only needs 6" cover - expensive, but the upside is you can trench it with a garden trowel.

Upside: smaller wire. 50A only requires #8 Copper THWN-2 instead of #6. Further, #6 Aluminum THWN-2 is also acceptable, for some cost savings, but this requires a socket which is CO-ALR rated. The breaker lugs are already aluminum rated.

Boxes at the pole

That's pretty easy. They already make a variety of outdoor boxes for mounting on poles, intended for RVs. Just use one of those.

You can get a simple one, that simply provides a receptacle.

Or you can get an RV "sub-panel", that provides a 50A, 30A, and normal common outlets all in the same panel. However, this will require installation of grounding rods on-site and a ground wire back to the panel must also be run. The ground wire deals with ground faults; the ground rod deals with lightning.

Certain applications will also require GFCI protection on the 50A circuit. If you need that, it needs to be a GFCI circuit breaker back in the main panel. Upside: the 120V socket doesn't need it now.

You come into the bottom of the box with conduit. Even if you use direct burial cable like UF, you must still use conduit for the rise from burial depth to the surface and on into the box. Remember your 6 AWG UF cable will require 2" conduit. Make sure your box has a knockout that big!

  • Is the expansion of GFCI to > 20A RV receptacles new with 2020? 551.71(F) only requires them for 15/20A, 125V RV receptacles... Dec 6, 2019 at 5:49
  • @ThreePhaseEel Gah, I'm getting it mixed up with boats. Thinking too much about British narrowboats as RV's. Dec 6, 2019 at 6:02
  • @ThreePhaseEel Also, my use of RV receptacles has made me assume RVs. OP hasn't stated the application. Might be an onboard EVSE. Dec 6, 2019 at 6:08
  • Thanks for the detailed explanation. Another way I can do is to not bury the wires underground, rather take it through edges of my home via fences; i.e., attach the conduit 2 inch above the ground to the outside wall and fence.. Does this change anything?
    – marc Katz
    Dec 6, 2019 at 12:11
  • 2
    @marcKatz Agreed with ThreePhaseEel, any outdoor conduit is a wet location so NM-B is still Right Out, and pulling cable through conduit is still masochism. Presume all outdoor conduit is 100% full of water 100% of the time; the defense happens in the wire insulation. Also the conduit needs to be tough enough to survive physical abuse i.e. rampaging lawnmowers; so Sched 40 PVC is no-go. Dec 6, 2019 at 15:35

NM doesn't belong here!

Since you're putting conduit down, you do not want to try to stuff that NM cable down your conduit, for multiple reasons. First and foremost, a buried conduit is a wet location, as per NEC 300.5(B):

(B) Wet Locations. The interior of enclosures or raceways installed underground shall be considered to be a wet location. Insulated conductors and cables installed in these enclosures or raceways in underground installations shall comply with 310.10(C).

This means that whatever wires or cables are inside your conduit must be rated for wet location use, and NM is explicitly prohibited in wet locations by NEC 334.12 point 4, as the paper separator in NM will wick up water and deliver it to junction boxes, leading to difficult-to-troubleshoot failures down the line:

(B) Types NM and NMS. Types NM and NMS cables shall not be used under the following conditions or in the following locations:

(4) In wet or damp locations

Furthermore, even if you switched to UF (which is wet location rated), you'd be simply setting yourself up to swear up a storm as you tried to stuff the UF cable down the conduit, both due to the space a 6/3 UF takes up within the conduit, and due to the stiffness of UF cable compared to the alternative, namely running individual THHN/THWN wires in the conduit. You'll need 3 6AWG stranded wires (2 hots, 1 white neutral) and a 10AWG stranded green or bare ground for this, but you'll thank us for this later when you can use reasonably sized conduit, such as 3/4" Schedule 40 PVC or RMC, or 1" Schedule 80 PVC (you can use 3/4" Schedule 80 PVC if you use a bare ground, but that makes for quite a tight fit), and still be able to pull the wires through it with ease.

The good news is that running conduit "as the crow files" is your best option, if at all possible, as it makes the conduit easier to find the easy way (vs. the hard way!) down the road, and also saves you materials and bend allowance compared to a more complex path. However, you'll want to come up the outside of the house with the conduit to avoid a subgrade penetration and its associated leakage hassles. This does require a LB body to make the turn into the house, going into the back of your electrical panel, but the LB also provides a convenient pull point to avoid having to do more work with the panel open than one absolutely needs to.

P.S. installing the conduit on the fence is fine, if a pain in the butt for bends, but doesn't change the equation any otherwise

While there's nothing stopping you from installing conduit on your fence, it does have the downside that you may need more conduit bodies in order to conserve the 360° conduit bend budget between pull points that the NEC gives you, in addition to the longer route taking more conduit and work in general. Furthermore, aboveground outdoor conduit is still a wet location, as per NEC 300.9:

300.9 Raceways in Wet Locations Abovegrade. Where raceways are installed in wet locations abovegrade, the interior of these raceways shall be considered to be a wet location. Insulated conductors and cables installed in raceways in wet locations abovegrade shall comply with 310.10(C).

  • Thanks for the detailed explanation. Another way I can do is to not bury the wires underground, rather take it through edges of my home via fences; i.e., attach the conduit 2 inch above the ground to the outside wall and fence.. Does this change anything?
    – marc Katz
    Dec 6, 2019 at 12:12
  • thank you all. I have a good understanding now.
    – marc Katz
    Dec 7, 2019 at 17:03

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