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I would like to run cable for an in-wall heater but not actually connect to the heater right now, I just want to get the cable run and connected to the sub-panel (along with all the other cables that we are running). That way, I don't have to bring in the electrician again later on. So can I run cable from a sub-panel to a junction box and put wire nuts on the three wires and leave the junction box accessible - covered by a box cover but not covered with dry wall? The work will be in a room that we will be renovating in the next couple of months. Does NEC allow this kind of thing?

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Putting a box in at the end of the future run, terminating the wires in nuts, and putting a cover on it is standard practice for a "future expansion" outlet of any sort -- putting a label on the cover indicating what it's intended for is a nice touch, but by no means needed by Code. In fact, you cannot "bury" the box behind the drywall -- it must remain accessible for later use/servicing.

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  • I agree. As long as the branch circuit is covered in the permit some jurisdictions don't require a final after the cover inspection.
    – Ed Beal
    Aug 9, 2016 at 3:40
  • Though as an alternative point of view, about 20 years ago I was involved with a church project where we wanted to put some wiring in place as above with wirenuts capping off live wires inside junction boxes covered with a blank panel. The journeyman electritian doing the work said that doing that was a violation of code. So, we just had him terminate the runs with standard outlets that we could then later on put what we wanted on. Another option could be to do as you plan, but not connect it at the breaker box end either, in which case the NEC wouldn't care about non-energized circuits.
    – Milwrdfan
    Mar 7, 2017 at 17:40
  • @Milwrdfan -- a blank junction box cover used there should not violate Code as far as I know -- did he give a chapter-and-verse cite?
    – ThreePhaseEel
    Jun 22, 2017 at 2:57
  • @ThreePhaseEel, no he did not cite chapter/verse. I'm not an electrician by trade, but it's possible that there could be a difference between commercial and residential in Iowa? Or, since this was on a dedicated circuit for a future video projector install on the ceiling of a gym (if I recall correctly - it was 20 years ago!), maybe being a dedicated circuit made a difference on whether the circuit needed to be terminated with an outlet rather than just wire nutted wire ends in a blank-covered box.
    – Milwrdfan
    Jun 23, 2017 at 19:39
  • @Milwrdfan -- doubt it's a commercial/residential or a dedicated circuit thing -- I think that "blank panel" might have referred to something other than a junction box cover in the situation you're talking about, or at least that's what the electrician was thinking
    – ThreePhaseEel
    Jun 23, 2017 at 22:09
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I actually agree with someone in the comments. Running wires to a location and leaving them "live, but connected to nothing" is inappropriate. It would never be allowed in conduit; you are expected to either pull useless wires or put them to a use.

In cable-in-wall construction, it is allowed to set unused cables due to the impracticability of accessing the walls later. However they should either be disconnected at both ends, or connected at both ends.

I suggest you put the wires to a use. Wire them in all respects for the future application, then fit the appropriate NEMA receptacle for the circuit run --

  • for a 15A/240V (no neutral) circuit, NEMA 6-15
  • for a 20A/240V (no neutral) circuit, one or more NEMA 6-20 or two or more (i.e. duplex) NEMA 6-15
  • for a 30A/240V (no neutral) circuit, NEMA 6-30
  • for a 15A, 120/240V circuit, NEMA 6-15 or 14-15, or if AFCI/GFCI are not required here, a common NEMA 5-15 with the hots split.
  • for a 20A, 120/240V circuit, NEMA 6-20 or 14-20, or if if no A/GFCI, then a NEMA 5-20 with hots split.

These would be generally useless (except the 5-15 or 5-20) but would justify leaving the circuit wired and hot. If an inspector asks, just say "homebrewing".

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