I'm planning on running 2-2-4 URD service cable to a tankless hot water heater. It's a long story, but I have to run from an outside load center underground and through the subfloor of a building built on piers. The tankless water heater calls for #6 wire since it draws 55 amps. I have some 2-2-4 already, so was just going to use that since it's rated to (at least) 75 amps. My question is, I'll have to sleeve the cable as it exits the ground and runs up through the bottom plate of the wall. How do I figure the conduit fill for service entrance cable? Treat it like THHN/THWN/THWN-2?

  • Is there a reason you want to direct bury this instead of simply having a conduit hung off the joists? Or is the outside LC in question not mounted on the structure in question? – ThreePhaseEel Jun 15 '19 at 13:11
  • Right, it's not connected to the structure. The cable will only be under the structure for a short distance then it's exposed (buried) to the meter can/load center. Since posting this, I read that the cable has to be RHH/RHW-2 for it to enter the structure. The cable I have is Southwire MHF, anyone know if that meets the standard? – Catldavis Jun 15 '19 at 13:30
  • Did you check 338.12 Uses Not Permitted 338.12(3) and 338.12(b)(1)(2) – user101687 Jun 15 '19 at 20:51

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