Finding Conduit sandwiched between flooring?

[danski0224]

In some areas near me, it was common practice to run residential conduit between the subfloor (1 x 6 lumber- pre plywood) and the hardwood floor.

There are sleepers installed on the subfloor, in line with the floor joists. The wood flooring is nailed to the sleepers. The sleepers are notched/cut for the conduit.

There is tar paper on top of the subfloor, so you can't see anything from below.

A stud finder doesn't work, nor did the AC alert function.

A circuit breaker finder didn't work.

A low voltage tone generator didn't work.

Short of x-ray scanning, any ideas?

Amprobe and others have a $1,000+ wire tracer, but I've never seen one used in the field. Looks great in the videos, but skeptical.

 

[Rusted Nut]

This would probably pick it up.

https://www.amazon.com/dp/B00SWIHA1E/?tag=atomicindus08-20

 

[mike93lx]

Wtf? Wonder what the Justification was

Load it up for a bit and try a thermal camera?

 

[dscheidt]

Wtf? Wonder what the Justification was

Load it up for a bit and try a thermal camera?

The choice is either this, or on the ceiling of the floor below. This is almost always rigid conduit ( or just straight out gas pipe), not emt, and there's no way in hell you're feeding through the joists. I expect a good strong magnet (try the rack-a-tiers studball, even if it doesnt owrk for this, it's amazing at finding nails in studs, even little ones for lath behind an inch of plaster) would find them.

 

[Just_Steve]

I have seen adds for a scanner for a smartphone to identify what's behind the wall.

 

[danski0224]

Wtf? Wonder what the Justification was

Load it up for a bit and try a thermal camera?

Just how it was done at some point. It's easier than drilling studs horizontally through the wall.

I have a thermal imager. IF it works, it would take a long time to show up through 3/4" or so of wood.

 

[danski0224]

This would probably pick it up.

I've had iffy luck with basic stud finders.

No way to know without buying and trying.

 

[alfredeneuman]

Use a "full blast" metal detector like those designed for detecting coins etc. at the beach.

 

[danski0224]

I have seen adds for a scanner for a smartphone to identify what's behind the wall.

The ads show scanning through drywall.

Granted, this is what most people are trying to do, scan through drywall.

 

[Innovate1]

Metal detector or magnet. They used to make and maybe still do a stud/nail finder that was a small magnet on a pivot. When run over a nail the small magnet would move as you passed over the nail. Not sure how welll it will work if the conduit has a thick wood cover. You should be able to get some idea where the run is from where the wires are at the ends - or are the wire exits hidden?

Found the nail finder:
https://www.acehardware.com/departments/tools/hand-tools/stud-finders/20887

 

[Innovate1]

The ads show scanning through drywall.

Granted, this is what most people are trying to do, scan through drywall.

I've seen the ads. Some sort of radar I think. Uses a phone as the display. I have been slightly temped to get one but haven't yet. Would be interesting to hear from an actual user here if anyone has gotten one.

 

[Just_Steve]

The ads show scanning through drywall.

Granted, this is what most people are trying to do, scan through drywall.

Agree but if this type of thing is down to the DIY person, I wonder what might be available in the pro realm, maybe at a large tool rental company.

 

[b-boy]

I have seen adds for a scanner for a smartphone to identify what's behind the wall.

I bought one of these. They don't work that well.

 

[danski0224]

I bought one of these. They don't work that well.

Aha.....

 

[sparky 1971]

One of these might be able to find them. The most powerful magnet for it's size I've ever seen. Don't get your fingers between the magnet and metal. It's also the best thing I've ever used for fishing an insulated wall.

https://www.amazon.com/dp/B00MW9A8AY/?tag=atomicindus08-20

 

[Rusted Nut]

I've had iffy luck with basic stud finders.

No way to know without buying and trying.

That is much more than a basic stud finder. I’ve located rebar 6” deep with one of those.

 

[Zeke]

One of these might be able to find them. The most powerful magnet for it's size I've ever seen. Don't get your fingers between the magnet and metal. It's also the best thing I've ever used for fishing an insulated wall.

https://www.amazon.com/dp/B00MW9A8AY/?tag=atomicindus08-20

That looks like a time saver/money maker.

 

[sparky 1971]

That looks like a time saver/money maker.

It is. I have lost two of the magnet leads that go inside the wall though. Both times they go stuck on something so bad that I broke either the chain of the pull string that was attached to it. Not quite as profitable when that happens, but it has paid for itself many times over.

Replacement Magnepull Bullet W/Leader

Replacement Magnepull Bullet W/Leader

www.techtoolsupply.com

 

[alfredeneuman]

The magnet from an old hard drive might work.
They are super powerful.

 

[rharman]

That magnetic nail finder from Amazon might not have enough pull. This little guy has worked really well for me on drywall or lath & plaster. I thought it was a gimmick but it works better than my expensive Franklin electronic one.

The Stud-Pop...

 

[danski0224]

I'm not sure about a magnet pulling through 3/4" of oak flooring.

The Stud Pop will (should) pick up the nails used to fasten the flooring.

For me, a scanner or wire tracer would have more additional uses vs a magnetic wire pulling setup. I had not seen one of those, so it is neat.

 

[sparky 1971]

I'm not sure about a magnet pulling through 3/4" of oak flooring.

The Stud Pop will (should) pick up the nails used to fasten the flooring.

For me, a scanner or wire tracer would have more additional uses vs a magnetic wire pulling setup. I had not seen one of those, so it is neat.

I don't know about 3/4" oak but I've found steel studs through two layers of 5/8" drywall with the roller part of the Magnepull.

 

[RyanE]

Pin locator like the one linked below (no affiliation, just a good example).

I use these to locate buried culverts and iron survey pins all the time. Sweeping across the floor you will very quickly locate the position of any steel/iron. If you sweep in a grid pattern, you should be able to identify your steel conduit easily. I've also used one to locate rebar in a sidewalk.

Pin Locator

 

[HoosierBuddy]

I'm confused. Is the conduit steel?

Cause if it's plastic a magnet isn't going to find it and it certainly won't find the copper conductor either.

Also...you can rent this:

Amprobe AT-2005-A for Rent, Advanced Wire Cable/Tracer/Locator

Advanced Wire Cable/Tracer/ Locator

www.transcat.com

 

[RPH]

Use your new induction heater to warm conduit. Then take a thermal image. It will show the location of it.

 

[Innovate1]

Pin locator like the one linked below (no affiliation, just a good example).

I use these to locate buried culverts and iron survey pins all the time. Sweeping across the floor you will very quickly locate the position of any steel/iron. If you sweep in a grid pattern, you should be able to identify your steel conduit easily. I've also used one to locate rebar in a sidewalk.

Pin Locator

Interesting. Looks like a common metal detector with a smaller, maybe longer coil for better detection and/or location of pins...

 

[rlitman]

...I have a thermal imager. IF it works, it would take a long time to show up through 3/4" or so of wood.

So, what's the rush? Plug in a space heater and give it a few hours. It WILL find that circuit. Don't believe me? Take your thermal imager to your refrigerator and you'll be able to trace that circuit too.

 

[sparky 1971]

I'm confused. Is the conduit steel?

Cause if it's plastic a magnet isn't going to find it and it certainly won't find the copper conductor either.

Also...you can rent this:

Amprobe AT-2005-A for Rent, Advanced Wire Cable/Tracer/Locator

Advanced Wire Cable/Tracer/ Locator

www.transcat.com

If it's PVC run right under 3/4 flooring any nail or screw 1" or longer is going to eff it up. It's steel and every time I've seen it done, which isn't very many times, it was rigid.

EDITED: spell check got me

 

[RPH]

We used the induction units with a rope style coil. This would be wrapped or laid out as needed. Power switched on causing the highway frequency energy to intersect with the metal. The metal would warm and the thermal picture would indicate rebar or conduit within bridge abutment, cement columns, and such. Very unique application.

 

[engineer2]

If it's near Naperville, a Chicago suburb, I can almost guarantee it will be EMT.
A thermal imager might pick it up if there is enough temperature differential. Put a 12 amp load on the circuit for a few hours to warm up the circuit and then try it. If you were closer, I'd try it with my thermal imager.
I can easily see a 2 degree differential. This is hot water subfloor heat through an area rug.

 

[danski0224]

It's EMT.

 

[American Locomotive]

Just get a giant neodymium magnet. Something like this :https://unitednuclear.com/magnets-c-70_79/1-w-x-34-thick-x-2-long-block-p-276.html.

I have a similar magnet, and it will pull strongly on steel 1+" away.

 

[danski0224]

If it's near Naperville, a Chicago suburb, I can almost guarantee it will be EMT.
A thermal imager might pick it up if there is enough temperature differential. Put a 12 amp load on the circuit for a few hours to warm up the circuit and then try it. If you were closer, I'd try it with my thermal imager.
I can easily see a 2 degree differential. This is hot water subfloor heat through an area rug.

I have a thermal imager and yeah, it will pick up hydronic loops.

It's certainly possible that something like a space heater, left on for a couple/few hours, will generate enough heat to show up.

One issue is time (or, was). The other one is missing that possible extra conduit run that's on a different circuit. Oh, and the company doesn't have a thermal imager, I do.

There is one spot left to cut out, and there is an outlet nearby. This hole is much bigger than the others, so the odds of hitting something are pretty good.

At the other locations, the customer decided to cut out part of the subfloor from the basement to do a visual for conduit at the locations I marked. This approach was mostly successful, but there were 2 locations where the conduit was just out of reach by hand and deemed "good to go".

Fortunately, the provided drill bit was not as sharp as it could be, and the delay told me that there was something else there. Other holes from below revealed the hiding conduit.

Yup, I suppose that a borescope up through the subfloor is a possibility, but the hole would have to be on an angle to get it into the ~3/4" space, and drill access is limited in the needed direction. Or something like a 1" hole and an articulating borescope.

The boxes in the walls are more like current "old work" boxes- only 1 device fits inside. The visible bigger boxes are more octagonal in shape but still will not fit 2 devices. I suspect this pre-dates what is now called a 1900 box. The in wall boxes have a conduit going straight down, and there is one off the side that also eventually goes down. So, depending on which side the load is connected to, the other part may not show up.

I have had a need to find buried stuff once in a while, just often enough to be a pain. Towards that end, the discussion interests me.

The multi-surface radar scanners look interesting, but again, more mixed reviews.

 

[danski0224]

I don't know about 3/4" oak but I've found steel studs through two layers of 5/8" drywall with the roller part of the Magnepull.

That's surprising, steel studs are not heavy gauge.

I can easily notice a difference sticking a magnet to a steel stud directly vs something like an I beam.

 

[danski0224]

The infrared imager works, it took about 3 hours to generate enough heat to show up.

One of the outlets doesn't have conduit in the way.

Waiting to check the other one.

 

[danski0224]

Other one was ok. Power fed from above.

 

[dave*99]

The choice is either this, or on the ceiling of the floor below. This is almost always rigid conduit ( or just straight out gas pipe), not emt, and there's no way in hell you're feeding through the joists. I expect a good strong magnet (try the rack-a-tiers studball, even if it doesnt owrk for this, it's amazing at finding nails in studs, even little ones for lath behind an inch of plaster) would find them.

Stud ball huh …… You just cost me $20. I had to have it.

 

[mike93lx]

The infrared imager works, it took about 3 hours to generate enough heat to show up.

One of the outlets doesn't have conduit in the way.

Waiting to check the other one.

Man, that was a hell of a good idea

 

[Innovate1]

Wondering what IR camera you have. We have an expensive one at work and they have gotten a lot better over the years. But a low cost home one would be handy.

 

[RPH]

This is the one I use. Excellent tool, good software too.

Flir One Professional Thermal Camera for iOS and Android Smart Phones | Flir

The Flir One (formerly Flir One Gen 3) is an affordable smartphone attachment thermal imaging camera designed to help professionals find problems faster and get more work done in less time. With MSX® (Multi-Spectral Dynamic Imaging) technology, which enhances thermal images by embossing details...

www.flir.com