Suppose I need to run power to an outbuilding. The line will run underground. Between the supply and outbuilding is a long, wide pond. Going around the pond isn't really feasible.

This is not a question about how to power equipment in a pond. Finding Code cites on this has been hard because Google is flooded with advice on powering loads that are in the pond, such as fountains or aerators.

I simply need to get across the pond. The pond will have ducks, otters, beaver, fish and humans.

What are the Code legal methods to carry the wires across the pond, and how do I transition between that and the underground run?

I am unable to drain the pond.


What we know won't work

First off -- a cable or conduit submerged in a pond is in something beyond a wet location from the standpoint of the Code, so our wiring method needs to be suitable for the conditions. Second, laying sticks of rigid conduit is probably not practical either -- you either have to pull or push the conduit across the pond or lay it from a boat, while making joints in the conduit every 10', and ensuring it bends properly under the forces involved, as any kinking or damage will make pulling the wire through it far more difficult.

Furthermore, any wiring method that uses anything other than an insulated copper wire for its grounding conductor is no good as well, as it violates NEC 682.31(A):

(A) Type. Equipment grounding conductors shall be insulated copper conductors sized in accordance with 250.122 but not smaller than 12 AWG.

As a practical matter, this rules out UF and USE cables, as well as armor-grounded or bare-wire-only grounded direct burial (jacketed) MC cables. Furthermore, neither cordage nor typical submersible pump cable is directly suitable for this application as they are unlikely to be robust enough to handle a long run across a pond. This leaves us with two general groups of options:

  1. Liquidtight flexible conduit (LFNC as LFMC to LFMC couplings do not seem to be a thing) with listed watertight fittings and appropriately rated cable (likely an unjacketed/multiplex submersible pump cable) inside as THWN or XHHW-2 singles aren't rated to sit in water 24/7/365
  2. Direct burial rated cables suitable for the application (some TC and MC constructions)

Going the conduit route

We will be using LFNC by the spool for a long run, or at least the longest coils you can get, here, to minimize the number of couplings to act as potential leak points. Furthermore, LFNC-B is the construction of choice for this application as all the LFNC to LFNC couplings I can find are for LFNC-B.

You can lay the conduit from shore, or from a small workboat if you prefer (remember your PFD!). Once the conduit's in from starting point to ending point, using listed LFNC fittings to transition into the boxes or handholes at each end, then pull an unjacketed (twisted multiplex) submersible pump cable through it -- individual type THWN wires are not rated for continuous submersion. Note that it may be necessary to use a wet-dry vac to "suck" the conduit dry before pulling, depending on if water was allowed to freely enter the conduit during the conduit-laying process, and it also may be a difficult pull due to the inability to install usable pull points underwater to conform with bending limits.

If you wish to go the cable route

If the above idea seems too difficult, then it is possible to do this using cable wiring methods, using either type TC-ER-JP (Tray Cable, Exposed wiring Rated, Joist Pull rated) cable or some type MC cables. TC-ER-JP has the advantage that it's cheaper and easier to run/handle; however, it will need conduit protection at the stub-ups as it's not suitable for exposed work outside of supervised industrial installations, which increases the difficulty of installation here. Jacketed MC is somewhat stiffer/harder to run and terminate, but can be obtained in a construction called MC-HL (Metal Clad, Hazardous Location rated), which offers some advantages for a submerged application -- the welded armor on MC-HL is basically watertight, and it's tested to survive a greater degree of abuse than ordinary type MC cable as well.

Either way, you'll need a cable construction that fits the following criteria:

  • Copper conductors, minimum 12AWG, with THWN (acceptable) or XHHW-2 (preferred) insulation
  • PVC outer jacket, direct bury/wet location rated
  • 3 conductors (hot, hot, neutral) + an insulated ground (for MC-HL, insulated ground wires can be obtained in control cable constructions only)
  • For type MC cable, MC-HL (continuous welded corrugated armor) construction is preferred, with AIA (aluminum interlocked armor) construction acceptable depending on availability and cable sizing.
  • Type TC cable needs to be TC-ER-JP (Tray Cable, Exposed usage Rated, Joist Pull rated) in order to be adequate for this application -- this ensures that it has a fighting chance at surviving abrasion and other such physical abuse

I would terminate the cable and trench it in to 24" topcover at one end, then use a workboat to lay the rest of the cable (remember your PFD!) to the opposite shore of the pond, where you can then trench in the rest of the cable and terminate it at the other enclosure. Termination is fairly simple here -- the insulated ground wire lands on a ground bar or lug within each enclosure, while the armor of type MC cable is terminated at the fitting. With TC cable, a suitably sized Schedule 80 PVC or rigid metal conduit can be used to provide stub-up protection; this is terminated normally at the enclosure, with the jacket cut off and the insulated ground wire landed on the enclosure ground bar/lug.


I spent a while searching around to cobble together an answer. You're right about this being unclear when it comes to underwater.

NEC, for instance, forbids underground wiring within 5 feet of a body of water

Underground wiring isn't permitted under bodies of water. Wiring within 5 ft horizontally of the inside wall of a body of water must be installed in rigid metal conduit (RMC), intermediate metal conduit (IMC), or a nonmetallic raceway system (680.10). Use the burial depths shown in Table 680.10.

What makes this confusing is that section 680 governs pools. As such, it doesn't seem to apply here (if you're installing a pool, you can set where the wires will run). I mention it because a LOT of search results got hung up on it (not in the least because it uses the vaguer "body of water" terminology). NEC 300.5 doesn't offer any help either, simply assuming that anything "below grade" will get wet, without having an explicit section for underwater.

I think it's safe to say we can lay wires on the bottom of the pond (many people reported doing so successfully). But what kind and how? After reading around, it's safe to say that UF isn't a good choice here (you yourself ruled that out long ago!). THWN-2 is OK, but there's mixed anecdotes of it being reliable in this circumstance. What looks like a good pick here would be the newer XHHW-2 wire. It's THWN's heartier cousin

XHHW-2 has XLPE insulation instead of the PVC insulation used in THHN wire.

This makes XHHW the more expensive option, but its coating is more resistant to chemicals, ozone and abrasions.

I would also say that conduit is a must here as well. To avoid any potential damage, I would go with stainless steel RMC conduit. PVC might do OK and save money, but if it doesn't, it will be a pain to re-run. Stainless steel offers the fewest questions here.

  • Love this site! I read through the first link about conduit under bodies of water and it denotes pool's, spa's and other manufactured water holding things as bodies of water. It however omits any reference to naturally occurring bodies of water. Do you think from a code perspective, in this case a pool and a pond are different? I only have the Canadian Electrical Code and it's a digital copy. I want to print it now. – Joe Fala Feb 22 at 4:43
  • @JoeFala -- in the US, the NEC deals with "bodies of water", both natural and manmade, under Article 682, whereas constructed pools, spas, and the like are handled under Article 680 rules. Compare 680.1 vs 682.1 for details. – ThreePhaseEel Feb 22 at 5:01

I think that you'll need a pole on each side of the pond and then have to run the line over the top. I don't see any other way if you can't go around.

I don't know if allowed or not but there is flexible liquid-tight electrical conduit that may be able to be dropped into the pond. Not sure what otters/beavers, etc. might do to it though.

  • 2
    The op is not asking fir alternatives to running the line under the body of water but what methods are approved for running it under the body of water – Kris Feb 23 at 2:53

UF wire should be sufficient and code compliant for the entire run. You can have some access points for making the run easier or sub panel for GFCI protection midway if the run is over 80 ft. I say this because GFCI manufacturers have a limit on the distance the GFCI will work before the voltage drop causes problems.

The tricky part will be securing the UF. Perhaps PVC

Edit: In light of NEC 682, the requirement to have the EGC insulated prohibits UF wire. But PVC with THWN midway with GFCI protections would solve this. NEC 682 has a lot of rules so be sure to read it and study it.

  • 1
    UF actually won't work since the EGC in UF is bare, in contravention of 682.31(A) – ThreePhaseEel Feb 23 at 4:58

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