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Foreword: I've been using UF wire for about 10 years now, and I've really grown to hate it. It's hard to work with, hard to strip, and hard to pull through conduit. I prefer all my underground wire to go through conduit, because WHEN something happens (and it will ... I've had lightning fry underground wires thrice in 10 years), it's much easier to replace when you don't have to dig it up again.

With that said, I'm starting a new project of lining my driveway with lamp posts. Due to voltage drop (600+ feet), I need 6 AWG wire. 6 AWG UF is HUGE and would require ENORMOUS conduit. I've never used THWN before, but after much research, it looks far easier to work with that UF. I've decide to go with THWN, instead.

The wire I'm getting is rated THHN/THWN-2/MTW/AWN, so it's suitable for dry AND wet locations to 90ºC. I know, obviously, that it isn't suitable for direct burial and MUST be in conduit from the breaker box to the lamp post. However, this is where things become less clear. I've looked through the Code thoroughly, and I haven't found any guidance that clearly applies to what happens once the wire enters the lamp post. I'll run conduit through the ground and up INTO the lamp post. This gets the THWN wire above grade. However, once I get into the lamp post, what then? Can I simply run the THWN up through the lamp post and join it to the conductors for the light fixture within the lamp post body? Must the light fixture wires be joined to the THWN in a junction box? Must I run UF wire through the lamp post from a junction with the THWN to a junction with the light fixture wires?

Any guidance on this would be appreciated. I'd hate to find out after pouring the concrete and mounting the lamp post that it doesn't pass the inspection.

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Are there any instructions with the lamp posts? Where are the fixture wires in the lamp post? Are you planning to connect the 6 AWG conductors to the fixture wires directly? –  Tester101 May 21 at 10:11
    
I'm used to the plain, hollow lamp posts that are basically pipes: No instructions, no junction boxes, and no factory wiring. Granted, that's not the post we're getting. We're getting a surface mount post, because my wife doesn't like the simple posts. The surface mount posts at the home stores that I saw don't have junction boxes or factory wiring in them. We ordered one we like better online, but we're still waiting on our template unit (we just ordered one for now to make sure we like it in person) to arrive, so I don't know if it specifically has a junction box or factory wiring in them. –  Nick Williams May 21 at 11:50
    
Posting the manufacturer, make, and model, or product SKU of the lamp post would allow us to look up the lamp post, and possibly provide more accurate answers. –  Tester101 May 21 at 12:09

2 Answers 2

up vote 1 down vote accepted

You've got a couple of options.

THWN Conductors

You could simply run THWN conductors inside the lamp post.

THWN Conductors

Underground Feeder (Type UF) Cable

You could also run a smaller gauge UF cable inside the lamp post.

UF Cable


In either case, you'll want the conduit to come up above ground. Either inside the lamp post, or next to it, depending on the post.

If the splices are underground, you'll want to use a splice method approved for wet locations. Conduit underground is considered a wet location. Even though the splices may be in a conduit body, it's still considered a wet location.

If the lamp posts have access panels built in to them, you can make your splices inside the lamp post. This would eliminate the need for a handhole or conduit body.

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Thanks for the thorough explanation! The first image is roughly what I had planned, but I'll put the junction above ground in the base of the lamp post instead of below ground. (The lamp post will have a wide, surface-mount base.) It's good to know that the THWN conductors are allowed inside the lamp post. –  Nick Williams May 21 at 18:07
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Splices CANNOT be underground unless they are accessible, such as with a flush garden box. Done as shown in the drawings above would not be complaint. –  Speedy Petey May 21 at 19:27
    
This is true, Speedy, and I was aware of this. I'm not exactly sure of Tester101's intentions in the drawing, but I'd bet he knew and meant this as well. –  Nick Williams May 22 at 3:47
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After reading my comment above see amended correct drawings.... Although I really see no reason at all for boxes. The splices inside the post are fine and quite trade typical, in everything from a post in someone's yard to the largest parking lot tower light. In such installations boxes would be superfluous. –  Speedy Petey May 22 at 11:17
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@SpeedyPetey The OP didn't link to a specific lamp post, so I didn't want to assume there was an access panel built into the post. If there is, then of course you could make your splices directly in the post itself. –  Tester101 May 22 at 11:38

Yes, you can run THHN/THWN conductors inside the lamp post and up to the fixture. No need to run the conduit all the way to the top.

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Thanks, Speedy! That's the information I was looking for! (I'll give it a day or so to make sure I don't get any conflicting answers before I mark this answer correct.) –  Nick Williams May 21 at 11:51
    
Effectively the lamppost is a conduit and/or junction box. All the commercial ones I've seen tend to be wired with THWN, so I'm pretty sure you are good. –  Ecnerwal May 23 at 2:17

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