Electronics > Repair
Finding fault location for broken power cables in walls
jh15:
Before changing anything, do you have to get a permit first? Then a town inspector, or can you do anything and have a town inspector certify your work. Or do you have to have a licensed sparky in the works. If one is fully capable of electrical work, say industrial electrician, not licensed for outside work, but doing one's own home.
Poroit:
G'day Calzap,
Would you consider cutting 100 x 100mm inspection holes in that 4 metre stretch of the South Wall?
If it is drywall ,then that is fairly simple to patch.
Yo might be lucky and find it first try.
bostonman:
--- Quote ---Put a fast pulse into the wire and watch for the reflection from the break. Since a nanosecond is about a foot the timing will give the distance to the break. There are oscilloscopes specialized for this.
--- End quote ---
I haven't done this personally, but I was with someone at my old job who did this. We were measuring the length of coax cable running in the building.
In any case, as you can see, plenty of creative options exist and this pulse suggestion is a really cool way of doing it. If I can recommend one simple suggestion and maybe it's not applicable. but sometimes I dissect problems by thinking about something logically such as: which route would someone run cable or you find a starting point and try to imagine the directions it takes.
Most likely this isn't applicable to your situation, but sometimes I just think about a manufacturing company and how they'd build something for speed or whatever the case may be.
calzap:
Problem with inspection holes is there are vertical studs at about 0.5 m intervals. So, a bunch of inspection holes would be needed for a 4-m stretch. In this particular case, I think things are even more complex. City water comes into the house in the same wall as the dead outlets. That’s why the sprinkler flow switch is in it.
Based on certain structural features, it appears a lot of the PEX and fittings were fastened in or on that wall when the house was replumbed. Then some new studs with lots of notches for PEX were fastened broadside to the wall, and those were covered with drywall extending floor to ceiling. It’s possible that all or most of the original drywall was removed.
And of course, that’s the 4-m section where the fault probably is. No surprise. That’s where the plumbers and carpenters did their sawing, drilling and fastening. So, best guess is there is a layer of drywall, 50 mm gap filled with PEX and fittings. Then maybe another layer of drywall. Then more PEX and electrical cables. There is no knowing at this point whether the new studs line up with the old. That’s why I’d really like to locate the fault as precisely as possible before drilling or cutting holes.
If I can’t do that, simplest fix will be to go in the attic and find the cable from the GFCI outlet. Install a junction box and drop a cable through the wall to the dead outlets. Haven’t been in the attic yet, so it may be more complex than described above.
Mike
antenna:
Could you disconnect the suspect 4m piece at both ends, then make a loop at one end, then grid-dip it? Maybe even use a nanoVNA and port extend noting the distance that way? Even if the RF couples to other lines, I sure would think the stub resonance would be apparent.
Never tried in practice though.
I was off by a decimal place on my TDR time, sorry, that scope may be fast enough
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