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I'm working with 6-3 UF-B wire in a wet location (under a deck). Does this wire need to be in conduit or buried? In other words, can the wire be exposed to the elements as is under the deck?

If there is no requirement for running in conduit, what are the advantages of doing so?

Edit #1 - The underside of the deck cannot be accessed without unscrewing deck boards.

Thanks.

  • The way I understand it, UF cable is rated for direct burial. There are situations and locations where it has to be protected from being damaged physically, that would be an advantage of conduit. Someone will hopefully post which situations require protection, it also could vary per local code enforcement authority. – Jimmy Fix-it Sep 18 '15 at 19:54
  • If the underside of the deck is accessible then conduit or similar protection is required. – Kris Sep 18 '15 at 20:24
  • @Kris, I disagree. Just because an area is accessible does not automatically mean it is an area that is "subject to damage". – Speedy Petey Sep 18 '15 at 22:37
  • @Speedy Petey, actually that is an interesting point. All UF/NM wire would require some form of protection regardless. However, only if accessible. – Kris Sep 18 '15 at 22:41
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    And it should be noted that Sch40 PVC affords no more protection than the cable itself in the eyes of the code. Sch80 would be required for protection. – Speedy Petey Sep 18 '15 at 22:49
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Since the deck itself protects the wire from physical damage and sunlight, you will have no problem running the UF exposed under the deck. Attach it to the side of a joist in the same way you'd do an indoor run of NM in an unfinished space, and treat it as 60 deg C wire for ampacity purposes.

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UF is designed and approved for direct burial. For direct burial, the required depth is 24" or less depending on AHJ or if it's under pavement, you'll have to read the Table 300.5 in the NEC to get the exact details. Your deck is not considered a building in the NEC so it will need to be buried. It also must not be exposed to sunlight unless the wire you use is specifically rated for it.

I can't remember if UF is compliant for being run in conduit, I don't think it is, but even if it is, it would be miserable pulling that through. Instead, if you use conduit, you should use THWN since the interior of the conduit is considered a wet location, and you must also use waterproof compliant splices if any are inside the conduit.

If you don't want to dig a 24" deep trench, you need to use conduit, and it needs to be protected either by still being 18" or more below grade, or use other means of protection from physical damage.

  • Also see 300.5(D)(1), which requires the cable to be protected where it emerges from the ground. – Tester101 Sep 18 '15 at 20:47
  • UF is also design and approved for above ground locations as long as it is protected from physical damage and not in direct sunlight.. 340.10(3,4) – Kris Sep 18 '15 at 22:15
  • Also approved to be installed in conduit diy.stackexchange.com/q/31149/37795 – Kris Sep 18 '15 at 22:21
  • I'm having problems finding the definition of "above/below grade" in this context. Can you define this exactly? Sorry I'm not familiar with this terminology quite yet. – Scott Lin Sep 19 '15 at 1:11
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    This answer is an example of why folks need to stick with their field of expertise. – Speedy Petey Sep 19 '15 at 11:07

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