What are the dangers of hidden boxes?

Question

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)

Answer 1

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.

Answer 2

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.

Answer 3

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).

Answer 4

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).

Answer 5

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.