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I'm installing a subpanel that will supply only 240V 2-pole devices. I'm positive I never will need the capability to run 120V (1-pole) devices. Am I required to run a neutral wire to the subpanel? Please don't provide answers that recommend I do it "either way" for future-proofing. I only want to know what is code-required.

The code for feeders talks a bunch about the required size of feeder grounded wire, but as far as I've seen it never comes right out and states that it is required to provide a grounded wire. I am of course providing a grounding wire.

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  • If I had a nickel for every person who was positive they'd never need - and then did - I'd be rich. But I'll leave the code question for someone else as I'm not sure off the top of my head.
    – Ecnerwal
    Dec 30, 2016 at 17:43
  • @ecnerwal The subpanel is only 10 ft from the main and is only feeding a tankless water heater that wants 3x 40 amp breakers (and doesn't have terminals sized to fit the gauge that would be required for the full current). The subpanel is going to be maxed out on capacity from the tankless heater alone.
    – David Pfeffer
    Dec 30, 2016 at 18:39
  • My guess is since code says the minimum size is specified in 250.122, that that size is not only the minimum but also required. But that's never stated, its just implied.
    – David Pfeffer
    Dec 30, 2016 at 19:54
  • I suspect the reference to "grounded conductors" in 215.2 is an error -- I'll have to yak at the NFPA next week though as they're closed for the holidays right now.
    – ThreePhaseEel
    Dec 30, 2016 at 21:42
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    I guess this: Are you allowed to designate a panel a 240V-only panel? Of course. What would a service panel like that look like? Like a 3-phase delta panel with only 2 phases, which would look exactly like a split-phase panel without a neutral bar. How would you source breakers for that? Normal 240V breakers. How would they even know they were on a 240 and not 240/120 circuit? They wouldn't. They already don't. How can that be wrong, and if it is wrong, how could something else be righter? I don't see how.
    – Harper - Reinstate Monica
    Dec 31, 2016 at 4:12

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Its fine, no different than the main feed to your house. NEC(1999) article 200 is "grounded conductors" and 215 is "feeders".

"200-2. General. All premises wiring systems, other than circuits and systems exempted by sections ... 215-7 ..., shall have a grounded conductor that is identified in accordance with section 200-6. ..."

and so

"215-7. Ungrounded Conductors Tapped From Grounded Systems. Two-wire dc circuits and ac circuits of two or more ungrounded conductors shall be permitted to be tapped from the ungrounded conductors of circuits having a grounded neutral conductor. Switching devices in each tapped circuit shall have a pole in each ungrounded conductor."

Meaning that you need to use double pole switches and breakers. (that disconnect both wires, as opposed to common light switches that only disconnect one of the wires.)

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