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I've been remodeling my 1924 house, and have been slowly re-wiring, and splitting up an old "mega circuit" where half the house is all wired into one circuit. In the process of doing so I discovered many hidden boxes buried in the basement ceiling. Judging by the type of wiring (cloth wire in bx) I'm guessing this dates to sometime from the 30s to the 50s.

I know this isn't right, and my goal is to remove all this old wiring, and de-energize this mess. The wiring connections inside these hidden boxes seem fine and not loose, though the wiring scheme itself seems to have been done by a madman channeling Rube Goldberg (which is much of the reason I'm re-doing it).

I'm curious about the larger picture here. What are the inherent dangers of a hidden box if the wiring connections are solid, but just foolishly covered up? It makes maintenance impossible without destroying things, but is that the extent of the problem? (And yes, I'm thinking about what old circuits I want to put AFCI breakers on)

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    Drilling into a hidden box seems a good one.
    – Solar Mike
    Nov 10 '20 at 6:13
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    @SolarMike - Wouldn't a bare cable be more likely to be damaged by the drill? If anything, I'd say the box adds protection. Nov 10 '20 at 12:53
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    @batsplatsterson seen a cable protected by a metal cover drilled through by an idiot - well I just pushed harder... :) it’s difficult to make things perfectly safe because idiots are so inventive.
    – Solar Mike
    Nov 10 '20 at 13:01
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    By the time you make something fool-proof, @SolarMike, they invent a better fool... :(
    – FreeMan
    Nov 10 '20 at 14:14
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    Likely there was originally no ceiling in the basement.
    – Hot Licks
    Nov 10 '20 at 22:40
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I have heard and even participated in lengthy debates on this subject. The code is very clear, and the difficulty in maintenance and troubleshooting is of course easy to see.

Many of the arguments go down the path of, "Aren't there other things permitted in the code that are just as likely or more likely to create a hazard?" But that's not the question here. The question is, what is the actual hazard created?

The same box and the same splices with the same connections in the same wall with an accessible cover plate is compliant; a layer of drywall over that cover plate and it's no longer compliant. How does the layer of drywall over the box make it more hazardous?

In fact, you can put a box in between the joists above a recessed light where you can get to it by removing the light. That's considered accessible. How is that more hazardous than the same box between two studs?

The answer is, it is not inherently more hazardous.

Don't do it; it's still against code, and still a bad practice; but it's not inherently dangerous.

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    The difference between a box behind a recessed light and a box behind drywall is that you know there's wiring connections behind the light. Nov 11 '20 at 6:57
  • @JosephSible-ReinstateMonica - that's not a safety issue Nov 11 '20 at 10:24
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    It becomes a safety issue when some unsuspecting person drills a hole in the wall to mount a TV bracket, and get a nasty surprise when they drill into a conduit box. Nov 11 '20 at 10:47
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    @spikey_richie - that was already mentioned in comments. The splice inside a buried box is no more vulnerable than an unprotected NM cable in the wall, in fact it is probably less vulnerable to drill damage. Nov 11 '20 at 10:52
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The main problem here is always troubleshooting (and if you're burying boxes you might be doing other dumb electrical things). Your circuit stops working one day, so you start to look for the issue. After ruling everything else out (boxes you can reach and crawl spaces or attics), you're now left with a couple of troublesome and costly options

  1. Open the walls and look for the problem
  2. Just run a new cable to fix the problem (which may entail #1 anyways)

Now, the chances of this happening are low (if you're burying a box, you probably have some sanity inside the box itself), but it's not zero. It's better to avoid the risk entirely and rerun the wire without the box, or make the box accessible.

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  • Think of it as a courtesy to future residents, which may be you again in 5-10 years - are you going to remember exactly where all the buried boxes are a decade later? Having lived in a house where the previous owner was a mad-scientist level DIY'er, I can appreciate properly accessible j-boxes the same way I appreciate properly commented code. (I assume some people on here are also programmers...) Nov 10 '20 at 16:48
  • @DarrelHoffman I've heard it as "Work to make your Future-Self grateful to Past-Self for forwards-thinking"
    – Criggie
    Nov 10 '20 at 18:39
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    If we're going with software comparisons, then burying junction boxes is escaping SQL (which is "safe enough", but has some places it might not work as intended) vs prepared statements (always safe). Why do something that is mostly safe, when you can do it always safe?
    – Machavity
    Nov 10 '20 at 18:39
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A safety-related problem with hidden junction boxes is that they can make it impossible to evaluate and correct dangerous conditions that might arise in future. If e.g. a home gets hit by a high-voltage surge, it may be necessary to inspect all of the junction boxes for signs of damage. A prerequisite for doing that, however, is finding all of the junction boxes.

A second issue relates to being able to list all of the loads served by each circuit and understand any requirements therefor. If a split-phase circuit is used to drive both 110V and 220V equipment, it must have a common-trip breaker. If a circuit were thought to only be driving 110V equipment, however, it might be reasonable to replace a common-trip breaker with a handle-tie breaker so that if one side of the circuit is overloaded one could identify the side on which the overload occurred. If a hidden junction box coupled the circuit to a 220V heater, however, an overload condition on half of the circuit when the heater is off might cause devices on that half of the circuit to be shut down, but if the header switched on the devices might spontaneously start up again (though with voltage reduced as a consequence of having the heater in series).

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  • He is asking given everything else being equal what is wrong with them, not common problems and issues that come from your average junction box. So given that the box was not hidden and met code, what is the difference if you drywall over it.
    – DMoore
    Nov 10 '20 at 19:12
  • @DMoore: If a home gets damaged by a power surge, by what means would anyone know to inspect the junction box that's covered over by drywall?
    – supercat
    Nov 10 '20 at 19:58
  • if your home gets hit by a power surge are you up in your attic checking the 4 junction boxes out?
    – DMoore
    Nov 10 '20 at 20:05
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    @DMoore: For a power surge like the one that hit my parent's house in the 1990s, probably. The surge was strong enough to fry the fusebox and weld a number of plugs into receptacles. It wasn't necessary to replace the wiring in the walls, but I think all known junction boxes were inspected since a power surge strong enough to weld a plug into a receptacle could quite plausibly damage wire nuts in unknown fashion.
    – supercat
    Nov 10 '20 at 20:26
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The problem is not that it is more dangerous. Unless you are mixing wire types (and they could build that into "new code") it is not more dangerous - AT ALL.

But... I hate it but I get it...

If you allow hidden junctions you are allowing the most half-assed, non-sense based circuit layouts and it is basically impossible to enforce any kind of "best practice". It isn't about having 1-2 strategic junction boxes in a house it is allowing some dumb ass "electrician" (who probably shouldn't be certified) to just do whatever he wants as long as it "works" right then.

However... I have gone through this more than a few times. Just put nice blanks on your junction boxes when you need 1-2 to save you from rerunning 10 outlets. I try to put blanks on the other side of an outlet stud and it looks good. I have also put junctions in oversized light fixture covers and things like that. I have actually gone around in circles with inspectors about the light fixture covers (and won).

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  • Well I mean most bad electricians aren't really electricians they are just guys that run wire with no certification. Not to say there are some truly horrible certified electricians but allowing junctions in walls basically gives a bad homeowner electrician an out for all of their shoddy work.
    – DMoore
    Nov 10 '20 at 18:23
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    @SteveSether - switching the neutral was a common practice in that time period and code compliant at the time, it's not a sign of poor workmanship. Nov 10 '20 at 21:31
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I believe from personal experience and anecdotally that the kinds of things you are seeing are common in homes from that era. I found a number of hidden boxes in my home when I pulled down ceilings and walls. Some turned out to not be in use but I found a couple at least that were energized. Talking to contractors who do renovations, they suggested that code may not have forbidden this at the time. I'm not sure if that's the case but alternately, perhaps enforcement was lax. I'm more concerned when I find bare splices to 'fix' damaged wiring.

I'm surprised that no one has mentioned this because I've seen it here before: one issue is that the most likely place for a fire or other issues is where wires are spliced.

If your wiring is this old you should really be looking to replace it anyway. The insulation on old wires gets brittle and cracks. Mostly not an issue in the wall but in outlet and switch boxes where the have been moved over the years, you can have problems. I have to assume that there's no dedicated ground either.

As far as the crazy wiring scheme goes, this is also common in older homes. To understand it you have to consider the structure before the walls were put up. The goal was to minimize wiring and effort, not to create a logical layout. While it might not make sense as an occupant to have an outlet on the same circuit as a ceiling light on the next floor down, they are physically close together which is more obvious when the floor and walls are open. So instead of being crazy or foolish, they were probably being (too) clever.

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