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I need some advice that I'm having problems finding any conclusive answers for.

We are moving an electric water heater that is on a 20amp circuit outdoors (we live in South Florida)

I plan on running 10/2 UF cable from the box, under the house about 30ft in a dry crawl space. Then exit and go up 8ft to the water heater.

The water heater will go into a galvanized steel enclosure against the house.

My issues is that I would like to protect the UF cable from where it exits the crawl space to where it enters the water heater enclosure. About 8ft (2ft from inside the crawlspace 6ft up to the top of the water heater enclosure). I believe 8" of protection is required by code anyways to protect against vermits and weed wackers...

I know UF CAN be ran through conduit, but I'm having a hard time determining the correct size and determining the easiest/best conduit to use...

Does anyone have any suggestions or see an flaws in this plan? Any help is greatly appreciated.

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    When I answered I thought you were thinking 8” as through the floor protection. But if you are talking 8’ from the ground level up to protect the UF you should use schedule 80 pvc conduit for the cost but I would go the entire way so it doesn’t look like a hack.
    – Ed Beal
    Commented Mar 30, 2020 at 16:31

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There isn't a chart that says a specific size, you have to calculate it from the exact cable size per NEC Chapter 9, Table 1, Note 9:

(9) A multiconductor cable, optical fiber cable, or flexible cord of two or more conductors shall be treated as a single conductor for calculating percentage conduit or tubing fill area. For cables that have elliptical cross sections, the cross-sectional area calculation shall be based on using the major diameter of the ellipse as a circle diameter.

So you need to measure or find a table from the manufacturer of it's actual size, do some math, then check inside diameter of raceway desired for maximum 53% fill. Even Sch 40 or 80 can make a difference.

Most electricians I have worked with won't even know off the top of their head what 10/2 UF works out to because they wouldn't even try to push UF through the conduit, it's difficult, ugly, and inconvenient. I would run 1/2" PVC and THWN conductors.

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    You are correct as far as fill but we don’t know what the OP is using? 2 or 3 wire with ground? Some are round and some are flat , the flat being more common is a real bugger with 4 wires. 1/2” no way even 3 wire. If the op has what I have it will be much easier depending on crawl space. You won’t find me running conduit under my house barely enough room for a young skinny man.
    – Ed Beal
    Commented Mar 30, 2020 at 20:33
  • The point was to not even try putting the UF into conduit, using individual THWN conductors instead.
    – NoSparksPlease
    Commented Mar 31, 2020 at 0:22
  • I understand your point but UF under a house instead of conduit is easier, remember most DIY haven’t worked with conduit. As I mentioned if their is limited space I use UF because it is easier and I have to purchase the UF but always have conduit and thhn/thwn on hand. This is 2 points for UF even though it is a bugger to feed through the pipe.
    – Ed Beal
    Commented Mar 31, 2020 at 13:22
  • Thank you all, yes the crawl space utterly sucks, about 1.5' of room and putting in conduit would be a royal pain. I'll use some large 1" conduit, it will be excessive, but for the short run I need will be worth the price and security.. thank you all for your input, I truly appreciate it.
    – Matt
    Commented Apr 2, 2020 at 15:45
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The answer is yes, you can run UF in conduit. For your short section this would be normal. I normally use 1 inch; it fits easily and the NM is not damaged. UF is slightly thicker but should fit it depends on the MFG; some are round and some are flat, 3 wire or 4 wire, etc. A water heater only needs 3 wire normally: 240v and ground with no neutral.

I usually have to have a section of metal flex conduit from the wall to a water heater to protect standard NM since smurf tube or non-metallic is not allowed and liquid tight is too expensive.

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There is no "easiest". UF-B in conduit will be a masochistic pull no matter what size you use, unless you go rather extreme like 2" or something.

You can use conduit either as a wiring method (the whole run from junction box to junction box being in conduit) or simply as a wire guard.

As a conduit wiring method, the conduit must be at least 138% of the wide width of the cable. The cable is 0.518" which means the conduit needs 0.715" inside diameter conduit. In other words 3/4" conduit of almost any kind will do.

As a mere guard from damage, it doesn't matter whether the conduit fill rules apply. It simply will not be workable to choke it down 1/2" conduit.

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    I have 1 inspector that occasionally wants verification if we use 3/4 especially if flat any scrapes and he wants It redone so I just started using 1” and he never messes with it (but to tell the truth it probably scrapes on 1” also when moving fast and not paying attention.
    – Ed Beal
    Commented Mar 30, 2020 at 20:28

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