Let's play "Find the hidden junction box"!

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Old 10-18-10, 04:39 PM
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Let's play "Find the hidden junction box"!

I need some methods here. Over the past several months I've been rewiring my mom's house. The kitchen is the last circuit I have to do. I started with the kitchen first, but put it on the back burner while I did the rest of the house. Why? Because somewhere between the first light fixture in the kitchen and the ceiling light in the hall/stairwell, there is a hidden junction box containing a crucial splice. The house was originally wired with only 4 circuits total. That means that everything in the kitchen is on one 15A breaker. Meaning you can't run the microwave and toaster or coffee pot at the same time.

Now I have pulled 4 new 20A circuits (2 countertop, refrig/lights, OTR microwave), and I have the kitchen itself done, but I can't get the new circuits into the kitchen until I find this junction box. So everything is tied together onto old wiring and on a 15A breaker for the time being. There are several obstacles which have foiled every method I have tried..

Heres the details..

- Walls and ceilings are mudwall. 1/2" thick cement slathered over steel mesh.
- All wiring is in conduit.
- No attic in this house. It has a flat tar/gravel roof. There is about 12" deep of airspace between concrete/rebar joists 20" OC above the ceiling, but no access to it without punching through ceiling.
- Original wiring is 12ga tinned copper, with rubber/cloth insulation. High end from the late 30's when the house was built.

I have a Fluke Fox/Hound set, but it does not work with the wires inside EMT. Is there a way to make the conduit itself carry the tone? I tried just clipping one lead to a wire and the other to the box, but that doesn't work.

I tried several stud finders, including those designed for thick walls and metal studs, but the metal mesh confuses them.

Tried a strong magnet to try to find the box cover, but no luck. I'm not sure how far a rare-earth magnet can penetrate cement though, since it didn't seem to stick to the metal mesh either..

So what else can I try? I do not have a boroscope nor do I have the $500 to buy one. I do have an oscilloscope and access to a function generator if someone can think of a clever trick using them.

And blindly knocking a hole is an absolute last resort. I don't feel like having to repair a mud ceiling.
 
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Old 10-18-10, 06:05 PM
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I might suggest using a metal fish tape and trying to tap it against the inside of the junction box and see if you can hear the tapping. This will probably involve 2 people.

Ridgid has an inspection scope that only needs a 3/4" hole or so. I don't remember the price. Milwaukee has one about $125.
 
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Old 10-18-10, 06:43 PM
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Originally Posted by JerseyMatt View Post
I need some methods here. Over the past several months I've been rewiring my mom's house. The kitchen is the last circuit I have to do. I started with the kitchen first, but put it on the back burner while I did the rest of the house. Why? Because somewhere between the first light fixture in the kitchen and the ceiling light in the hall/stairwell, there is a hidden junction box containing a crucial splice. The house was originally wired with only 4 circuits total. That means that everything in the kitchen is on one 15A breaker. Meaning you can't run the microwave and toaster or coffee pot at the same time.

Now I have pulled 4 new 20A circuits (2 countertop, refrig/lights, OTR microwave), and I have the kitchen itself done, but I can't get the new circuits into the kitchen until I find this junction box. So everything is tied together onto old wiring and on a 15A breaker for the time being. There are several obstacles which have foiled every method I have tried..

Heres the details..

- Walls and ceilings are mudwall. 1/2" thick cement slathered over steel mesh.
- All wiring is in conduit.
- No attic in this house. It has a flat tar/gravel roof. There is about 12" deep of airspace between concrete/rebar joists 20" OC above the ceiling, but no access to it without punching through ceiling.
- Original wiring is 12ga tinned copper, with rubber/cloth insulation. High end from the late 30's when the house was built.

I have a Fluke Fox/Hound set, but it does not work with the wires inside EMT. Is there a way to make the conduit itself carry the tone? I tried just clipping one lead to a wire and the other to the box, but that doesn't work.

I tried several stud finders, including those designed for thick walls and metal studs, but the metal mesh confuses them.

Tried a strong magnet to try to find the box cover, but no luck. I'm not sure how far a rare-earth magnet can penetrate cement though, since it didn't seem to stick to the metal mesh either..

So what else can I try? I do not have a boroscope nor do I have the $500 to buy one. I do have an oscilloscope and access to a function generator if someone can think of a clever trick using them.

And blindly knocking a hole is an absolute last resort. I don't feel like having to repair a mud ceiling.
How is that junction box going to help you? What do you expect it contains? You'd think if that junction exists, it might be the center point of a fork in the to-kitchen/to-hall and ? circuit.

Do you expect to find 4 hot wires up there so you can tap in and create 4 kitchen circuits from there? That doesn't seem likely.

Just trying to figure out what you think is in that junction box, that makes it very valuable for all those new circuits you ran.
 
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Old 10-18-10, 08:13 PM
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Originally Posted by pcboss View Post
I might suggest using a metal fish tape and trying to tap it against the inside of the junction box and see if you can hear the tapping. This will probably involve 2 people.

Ridgid has an inspection scope that only needs a 3/4" hole or so. I don't remember the price. Milwaukee has one about $125.
The fish tape sounds like it's worth a try.. I don't see a $125 Milwaukee scope, quick googling turns them up for $250+, which is still more than I want to spend on it. I could swing $125. Got a model number or link?

Originally Posted by ecman51` View Post
How is that junction box going to help you? What do you expect it contains? You'd think if that junction exists, it might be the center point of a fork in the to-kitchen/to-hall and ? circuit.

Do you expect to find 4 hot wires up there so you can tap in and create 4 kitchen circuits from there? That doesn't seem likely.

Just trying to figure out what you think is in that junction box, that makes it very valuable for all those new circuits you ran.
First of all, this box is in between the kitchen and the source. The light in the hall connects to the conduit that goes to the old breaker box (which is now gutted and used as a pullbox). So I have 4 new circuits pulled up to the hall light box (remember, EVERYTHING is in conduit). Then there's a conduit that goes between the hall light box and the hidden box. Then from the hidden box goes to the first ceiling box in the kitchen. That hidden box is also where the range hood (now OTR microwave) outlet and exhaust fan wiring pull power from (I'm assuming, unless I have 2 hidden boxes to look for, since those are the only two unaccounted for outlets)

If it were just powering those two outlets, I'd just slap it on its own circuit with a 15A AFCI and call it a day. But it is the main feed into the kitchen, and until I find it, I can't split off the circuits. And being as it is older than dirt wiring, even though it is 12ga, I don't feel comfortable upping it to a 20A breaker It was originally on a 17.5A breaker (SquareD 4 way multibreaker, 70A total). It is a weak link in the wiring.

There is also no real 'logical' place for it either. There was a hidden box in another part of the house, but I was able to find it pretty much by luck. It was covered with paper and halfway built into the wall in a closet. So I expect no less idiocy on this one.
 
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Old 10-18-10, 09:21 PM
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How about a FLIR camera? Not sure how those would be with wire mesh, or an interior cavity, but with lath and plaster on an uninsulated exterior wall the conduit behind stood out beautifully. They're not cheap but maybe you can rent one or find a contractor or energy auditor who'd give it a half hour for a reasonable price.
 
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Old 10-18-10, 09:33 PM
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Old 10-19-10, 06:34 PM
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Originally Posted by JerseyMatt View Post
And being as it is older than dirt wiring, even though it is 12ga, I don't feel comfortable upping it to a 20A breaker
This is a point you raise that I think many people overlook. They think 12 ga. automatically means 20 amp. But with old wiring, where people in the past have perhaps reworked the wiring here and there, and it got cut, crushed, flexed back and forth one too many times, or whatever, to a smaller gauge or weakened at those defects - could be a source for a fire. And maybe some of these mysterious electrical fires that occur? - maybe it is sometimes for that reason. Maybe the 12 gauge wire winds up at about 18 gauge or something.
 
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Old 11-07-10, 04:41 PM
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Update! And another question..

So I found while wandering Home Depot, Ryobi has a $140 inspection scope which did the trick. I found the box. It is inside the pantry closet, above the duct for the exhaust fan. No wonder I couldn't find the damn thing. It isn't even close to the ceiling.





As you can see there are two EMT and two old school BX coming together here. Aside from the fact that I'm not going to leave a concealed joint, I can barely see the box at the angle through the hole (I had to cut the duct to get at it in the first place). So I'm going to have to install a nice deep square box in the wall next to the fan hole and extend the EMT to it. I have a couple rolls of smurf tube laying around, do they make a coupler to transition from EMT to smurf? And it should be acceptable to change from rigid to flex in a concealed space as long as there is no joint in the wire, right?

There is enough slack in both pieces of BX that I should be able to just move them over to the new box. They are also short enough pieces that I SHOULD be able to yank the old wires out of them and replace them with THHN. As long as I can get a green ground in there (which I should, because THHN is about half as thick as this stuff), does anyone see a problem with that? (I know it was sorta discussed in another thread, but that was just adding a ground, not gutting the old BX and running all new wires though it as if it were FMC)
 
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Old 11-07-10, 08:28 PM
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I think that you could use whatever fittings necessary to go from the EMT to the Smurf; a compression style box connector on the EMT to a rigid coupling to a threaded (plastic) adapter that would glue onto the Smurf. You would, of course lose any inherent grounding via the EMT so you need the equipment grounding conductor run complete from source to load.

As for pulling the old conductors from the BX...that isn't kosher since BX is an assembled cable and pulling the old conductors out and pulling new conductors in (even including an insulated equipment ground) is not code compliant. Even if you "call" the BX flexible conduit I think there is a specific code requirement that does not allow 3/8 inch "trade size" (which is what that BX would be) for use in field wiring. Can you perhaps snake some Smurf in place of the BX?
 
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Old 11-07-10, 08:52 PM
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Yeah I know on the ground. I've been pulling greens through the whole house anyway so as not to rely on the integrity of the conduit. So no issue there..

The one BX wouldn't be a problem because it'll most likely be abandoned in the near future anyway (the original exhaust fan is a plug-in, and the BX feeds that receptacle. I'm considering options now for a new/better fan that'll be wired in). The other one though goes to the OTR microwave (naturally the one I really need), and it is set into concrete. I can not pull the spiral out.
 
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Old 11-07-10, 09:16 PM
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The other one though goes to the OTR microwave (naturally the one I really need), and it is set into concrete.
Okay, you didn't read it here but under those circumstances I would probably just pull the three new THHN conductors through the BX. It won't be legit but neither would it be unsafe. Be sure to use the plastic anti-short bushings in the ends of the BX.
 
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Old 11-07-10, 09:39 PM
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a compression style box connector on the EMT to a rigid coupling to a threaded (plastic) adapter that would glue onto the Smurf.
I think I'd make that a female threaded PVC adapter and drop the rigid coupling.
 
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Old 11-07-10, 09:42 PM
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Hummm.,

Just a quick note you will not able pull the new conductor thru the old BX cable so the only legit alternative way you can do is pull the MC { metal clad } cable and you will have to figure out a way to make that junction box open or make a note where the junciton box is located { I will never leave it hidden }

Or the other alternative way is get a old work cut in box and get half inch greenfeild flexibale metal conduit and adpator fitting on the EMT or Steel pipe fitting and move it over the wall where you can able work with out issue.

Merci.
Marc
 
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Old 11-07-10, 09:59 PM
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Originally Posted by CasualJoe View Post
I think I'd make that a female threaded PVC adapter and drop the rigid coupling.
As long as it's legal, I'll see what HD has to make it work with as few fittings as possible.

Originally Posted by french277V View Post
Hummm.,

Just a quick note you will not able pull the new conductor thru the old BX cable so the only legit alternative way you can do is pull the MC { metal clad } cable and you will have to figure out a way to make that junction box open or make a note where the junciton box is located { I will never leave it hidden }

Or the other alternative way is get a old work cut in box and get half inch greenfeild flexibale metal conduit and adpator fitting on the EMT or Steel pipe fitting and move it over the wall where you can able work with out issue.

Merci.
Marc
The problem is, the BX is set into (not just running through a hole drilled into) concrete. There is no way whatsoever to replace that without busting into the wall, which isn't going to happen anytime soon..

I know not to leave the junction hidden, I had no intention of it. I was going to use smurf tube, since I have that onhand and the conduit isn't being used for grounding. That's why I asked about a connector to join it to EMT so I can extend it out to the wall.. That box isn't big enough anyway, because there will be 4 separate circuits running through it now, as opposed to one big splice on one circuit, so I'm going to put in a 4x4 deep box with a mud ring, and just put a double blank plate on it, rather than have to paint a regular metal cover..
 
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Old 11-07-10, 11:41 PM
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The last part you suggest that is a workable idea and yes that is wise to use the deep 4X4 box with mudring that help a bit.

Merci.
Marc
 
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Old 11-08-10, 01:37 AM
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I agree with Casual Joe's suggestion of a female PVC adapter. I so seldom use those I forgot they even exist.
 
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Old 11-08-10, 05:48 AM
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Originally Posted by ArgMeMatey View Post
How about a FLIR camera? Not sure how those would be with wire mesh, or an interior cavity, but with lath and plaster on an uninsulated exterior wall the conduit behind stood out beautifully. They're not cheap but maybe you can rent one or find a contractor or energy auditor who'd give it a half hour for a reasonable price.
This can work well in conventional stud walls and similar construction if the box is in an exterior wall or ceiling, and you arrange the IR inspection at the right time of day.

For example, here's a hidden junction box that was covered with drywall at the ridge of a cathedral ceiling (likely, for a ceiling fan):



you can't see the wiring as it not in direct contact with the drywall and is not conducting heat to the drywall's backside , but the edges of the box are clearly visible where they conduct heat from direct sunlight on the roof through to the drywall:


There are a number of such uses for IR imaging, and I keep finding more as I get more familiar with the technology:

Infrared Inspections for Electrical and Plumbing Components In Walls And Ceilings - Paragon Infrared Inspections Chicago
 
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Old 11-08-10, 09:32 AM
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Originally Posted by JerseyMatt View Post
The problem is, the BX is set into (not just running through a hole drilled into) concrete. There is no way whatsoever to replace that without busting into the wall, which isn't going to happen anytime soon..
Any chance you could go to surface raceway like Wiremold on the concrete face?
 
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Old 11-08-10, 10:54 PM
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JerseyMatt.,

Just let you know not too long ago I just have one customer in his house I allready found 30 hidden junctions boxes that was even more tougher than your part.
BTW., that is my record of numbers of hidden junction boxes I found in a house.

Merci.
Marc
 
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Old 11-08-10, 11:38 PM
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I just saw an episode of Holmes on Homes where Mike found something like 25 hidden boxes between the two rooms he gutted. I can't believe people do that. It's absolutely infuriating. I was lucky, there was only two in the entire house. Well, there's still another one I haven't found, but that's not electrical, it's the one where the 'antenna' outlets from all the rooms come together. That will just be a bonus when i find it because it'll be used for satellite and cat5 lines.

Ben, I'm going to just abandon that BX line. I stuck my camera up into the void and found a space where I can run a new line into the cabinet with minimal destruction.
 
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Old 11-08-10, 11:45 PM
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Originally Posted by JerseyMatt View Post
I just saw an episode of Holmes on Homes where Mike found something like 25 hidden boxes between the two rooms he gutted. I can't believe people do that. It's absolutely infuriating. I was lucky, there was only two in the entire house. Well, there's still another one I haven't found, but that's not electrical, it's the one where the 'antenna' outlets from all the rooms come together. That will just be a bonus when i find it because it'll be used for satellite and cat5 lines.

Ben, I'm going to just abandon that BX line. I stuck my camera up into the void and found a space where I can run a new line into the cabinet with minimal destruction.
JerseyMatt I do see Mike Holmes's show from time to time and I have see few crazy stuff what some of unlicensed person done like that. Tell you the truth no matter which place I am at { either in Wisconsin or Paris France } it will always be the same story.


And I am glad you found a new way to deal with it with minium of destruction.

Merci.
Marc
 
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