EEVblog Electronics Community Forum
General => General Technical Chat => Topic started by: TerraHertz on October 11, 2019, 03:29:49 pm
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Here's an example of that almost happening.
Yesterday my (very) old mum phoned me and said a bathroom light had come on by itself for a while, then gone off, and doesn't work now.
Today I went round there to have a look.
It's a softwood timber frame house, and that bathroom has western red cedar wall paneling. I noticed a strong burning smell.
Flicked the light switch, and can feel there's something mechanically wrong with it, but the light does turn on and off.
Turned off the lights power at the meter board then pulled the switch out of the door framing.
Urrgh. There's a recent termite invasion, and they made a nest in the switch cavity. Their nest building material is apparently somewhat conductive. It resistively heated up with the 240VAC current, and started a slow burn-back of the wiring insulation. That had gone about 4 inches back up the wiring, through the woodwork. It was all still warm to the touch, and the timber is charred.
The fuse (old style wire, not circuit breaker) didn't blow. Would have been better if it had. An earth leakage breaker wouldn't have helped with this.
Quite a close call I think.
Edit to add: Speaking of termites, what's with the bug in the photo upload selections? The photo you specify first, appears as the last one in the page, though the others are all in correct order. To get them ordered right here, I had to specify 4473 twice, then delete the "first" one (appearing as the last one.)
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:wtf: :o :o :o :o :o
Holy crap!!! That might not have ended will! Good thing you caught it when you did!
Edit to add - I'm surprised to see that the switch appears to be set directly into the wood, with no box of any sort.
-Pat
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Your guardian Angel is strong.
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Good find.
This is the type of thing that arc fault interrupter circuit breakers are meant to address.
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Probably a very old installation, and grandfathered into the modern regulations, as there pretty is nothing about having to upgrade all installations electrically as the regulations change, only that it must comply to the regulations applicable when built, and that anything that is done repair wise must be like for like, otherwise it is an "upgrade" and the upgrade must comply with current regulations.
Thus here you find a house that is a century old, and which has been in the same family for that time, and thus still has the original fuse box with wire fuses in it, fuse wire on a card for the replacement of them, and gutta percha wire though the house. Still complies, till you want to change a plug outlet, because 5A socket outlets are pretty rare, nothing easy to find plugs for, and the bakelite has disintegrated. Then you have to pull in new cabling to the distribution board (and find the @#$%^ sparkie cut cost, because he only pulled in a new red live wire instead of pulling in new line, neutral and an earth conductor), put in a new distribution board with mains isolator, earth leakage and 20A breaker, fed from the old board as a sub board, to get the installation to comply with the modern regulations. Then you find the bonding on the water pipes has failed, the grounding at the meter has rotted away, and the only ground the system has is the rather dodgy wire on the overhead 3 wire feeder that leads to the light pole outside, original to the house 90 years ago, and , as it falls on the boundary, is not checked by home owners, and ignored by the Metro electricians unless the wires have all fallen off.
Biggest shock on selling the house is the electrical compliance, as often you then have to replace everything to get it up to code, as the act of checking the wiring inside the sockets, switches and lights is often enough to cause the brittle insulation to turn to powder.
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This video shows how one homeowner dealt with roaches but it should work for termites too. After that you need not worry about the termites burning the house down.
https://youtu.be/ZFdu-HcyOx4?t=160
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Good find.
This is the type of thing that arc fault interrupter circuit breakers are meant to address.
And I await proof that (the ones being pushed here, anyway) actually operate in any real-world condition instead of a carefully created arc between two contacts opened by micrometer.
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Good find.
This is the type of thing that arc fault interrupter circuit breakers are meant to address.
And I await proof that (the ones being pushed here, anyway) actually operate in any real-world condition instead of a carefully created arc between two contacts opened by micrometer.
Well, I know the ones here in the US damned well trip consistently if you try to run motorized power tools on them! I have to run an extension cord to a non-AFCI 'protected' receptacle if I need to use my miter saw in the house. :rant: :rant: :rant:
-Pat
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AFIs are all shit. The 120V ones false trip and the 240V ones don't do anything (see John Ward).
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I'm very confused. Where was the "arc" that an AFCI might have detected? Looks like simple I2R heating was responsible for this near-disaster.
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Edit to add: Speaking of termites, what's with the bug in the photo upload selections? The photo you specify first, appears as the last one in the page, though the others are all in correct order. To get them ordered right here, I had to specify 4473 twice, then delete the "first" one (appearing as the last one.)
It’s the new “improved” image upload plugins recently added to the forums on a whim. It’s possible each of the two plugins in question work fine in isolation, but at least in combination, it’s buggy as hell. In the thread about it, I characterized the behavior in detail, but the admins haven’t taken any action (or even acknowledged that it’s buggy).
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I'm very confused. Where was the "arc" that an AFCI might have detected? Looks like simple I2R heating was responsible for this near-disaster.
Yup the AFCI would have been happy as a clam, saying to itself, Granma just turned on her tea kettle, I will help her. Once a combustible nest of fluffy high surface area has been built by the critters it will take bugger all total energy to start runaway ignition. Just look on the Youboob for bush-crafters starting campfires with the most feeble embers imaginable. The kind you get from a fire drill where you rub one stick on the other.
In the southern parts of Canada we do get termites but more often this kind mischief is cause by squirrels or other rodents.
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Wow :o seen a few of these but not this bad,
great pics btw :clap:
fwiw after a clean up and rectify on old school jobs like this, assuming it's an isolated one off incident, and not an infestation to be sorted with a complete rewire/outlet job
a shot of insect crawling spray into a suss electrical cavity,
and rub some around the back of the switch or socket housing, be it new or old,
then let it dry and or soak up any excess before putting it back as it was, complying to the regulations applicable when built
as commented by SeanB above .
Use GLOVES when messing with this stuff and a low odour insect crawling spray if people are close by, or sensitive to the vile smell of the good stuff
Rest assured termites and other crawlie groups will set up shop elsewhere next time.. :scared: :scared:
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@SeanB actually the house is not that ancient. It was built around 1970, and the wiring is PVC insulated. The intact insulation isn't brittle at all. Those wires near the switch are bare because the 'hot spot' of conductive carbonizing worked it's way along the wire like a burning fuse cord. Then the resulting gunk fell off when I moved them.
A pest eradication is going to happen urgently. In the meantime I went and bought a couple of cans of surface spray, broke open all the termite tracks I could find, and gave the entire area in the wall cavities and under the house a good dose.
I found where their trail comes up from the ground. It's inside a brick double wall, under the bathroom concrete slab. Looks like a metal wall capping there may have rusted through, but I can't see the hole. Rust suspected due to an in-wall toilet cistern made of plastic, that developed a crack and leaked some years ago. I fixed that, but it hadn't been leaking long enough to rot the timbers so I had only needed to replace sodden wall plaster and some tiling.
Before hiring the eradicators, I'll hammer-drill some big holes in the internal wall of the double brick, for access to that space.
My mum is 90, and probably only has a few years left. After she passes that property will be sold and it's virtually certain a buyer would demolish the house and rebuild. So, minimal effort repairs.
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Note that thermite could do that as well.
:P
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:wtf: :o :o :o :o :o
Holy crap!!! That might not have ended will! Good thing you caught it when you did!
Edit to add - I'm surprised to see that the switch appears to be set directly into the wood, with no box of any sort.
-Pat
Not a major drama, if, as is normal, there is enough clearance around the switch.
All but one of the light switches in my place are mounted into the trim around the door frame.
Most of the power outlets (GPOs in Ozspeak) are mounted into the skirting boards.
The other GPOs are set into the double brick wall, as is the light switch in the lounge room.
Termites absolutely love softwood.
I remember at my Mum's place, the electrician had used a bit of pine embedded into the brick wall to fit a light switch (the old round "surface mount" type).
The termites ate their way up the jarrah door frame (jarrah heartwood is not their favorite), & completely hollowed out the pine.
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Watch out who you hire for 'pest control'
Some are smooth talking rats in human form that rid you of one problem, at not so cheap 'professional' prices,
and ensure they come back again for another future problem.. they planted whilst underneath or out of sight.
Shop around for good operators via referrals that know their job and get plenty of work,
not turkeys that resort to 'making work' to bleed unaware battlers out of their cash
Don't ask me how I know this$$$... |O
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@SeanB actually the house is not that ancient. It was built around 1970, and the wiring is PVC insulated. The intact insulation isn't brittle at all. Those wires near the switch are bare because the 'hot spot' of conductive carbonizing worked it's way along the wire like a burning fuse cord. Then the resulting gunk fell off when I moved them.
A pest eradication is going to happen urgently. In the meantime I went and bought a couple of cans of surface spray, broke open all the termite tracks I could find, and gave the entire area in the wall cavities and under the house a good dose.
I found where their trail comes up from the ground. It's inside a brick double wall, under the bathroom concrete slab. Looks like a metal wall capping there may have rusted through, but I can't see the hole. Rust suspected due to an in-wall toilet cistern made of plastic, that developed a crack and leaked some years ago. I fixed that, but it hadn't been leaking long enough to rot the timbers so I had only needed to replace sodden wall plaster and some tiling.
Before hiring the eradicators, I'll hammer-drill some big holes in the internal wall of the double brick, for access to that space.
My mum is 90, and probably only has a few years left. After she passes that property will be sold and it's virtually certain a buyer would demolish the house and rebuild. So, minimal effort repairs.
Even really old houses in Oz are unlikely to have anything other than PVC insulation.
There was a bit of a paroxysm in the Electrical industry in the mid 1950s, with the widespread adoption of PVC for both cable insulation & power plugs -- the classic PVC Oz plug dates from about that era, with just a few mods having occurred over the years.
Certainly, in WA, even 100+ year old houses have been rewired with PVC over the many years since then.
I had occasion to climb around in the roof of a "Federation" era house, & came across some "tramline" type wiring.(bare copper wire supported by porcelain standoff insulators).
It had long ago been disconnected, & the wiring in use was all PVC.
An interesting sidelight ---someone in the past had put a TV antenna inside the roof, which does work OK with tiles, but not with a metal roof like this house had.
The antenna was resting across both sides of the old "tramline' wiring, so it's just as well it had been replaced.
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:wtf: :o :o :o :o :o
Holy crap!!! That might not have ended will! Good thing you caught it when you did!
Edit to add - I'm surprised to see that the switch appears to be set directly into the wood, with no box of any sort.
-Pat
Not a major drama, if, as is normal, there is enough clearance around the switch.
All but one of the light switches in my place are mounted into the trim around the door frame.
Most of the power outlets (GPOs in Ozspeak) are mounted into the skirting boards.
The other GPOs are set into the double brick wall, as is the light switch in the lounge room.
Another example of the massive differences in regulations between countries. At least in North America, switches and outlets are required to be in junction boxes and that rule has been around for probably close to a century.
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Certainly, in WA, even 100+ year old houses have been rewired with PVC over the many years since then.
I had occasion to climb around in the roof of a "Federation" era house, & came across some "tramline" type wiring.(bare copper wire supported by porcelain standoff insulators).
It had long ago been disconnected, & the wiring in use was all PVC.
An interesting sidelight ---someone in the past had put a TV antenna inside the roof, which does work OK with tiles, but not with a metal roof like this house had.
The antenna was resting across both sides of the old "tramline' wiring, so it's just as well it had been replaced.
That sounds like what's known in the states as "knob and tube" wiring. I've seen it in a few old houses (even still in use in a few lighting circuits at a friend's 1920s-ish house). The knobs are porcelain insulators used to support the wire, and hold it where turns were made, and the tubes were porcelain sleeves with larger heads at one end the were fitted in a hole wherever the wiring passed through a rafter, joist or wall stud. I'm happy that I can just pull a single cable with hot, neutral and ground all in one these days. MUCH easier!
Another example of the massive differences in regulations between countries. At least in North America, switches and outlets are required to be in junction boxes and that rule has been around for probably close to a century.
Right? It is amazing how much different the standards and methods for things like this are depending on where you are in the world! I'm not sure when junction boxes became a requirement in the US, (don't have anything on wiring going back that far), but even the knob-and-tube I mentioned above at my friend's house came together into boxes at fixture and switch locations.
-Pat
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The fuse (old style wire, not circuit breaker) didn't blow. Would have been better if it had. An earth leakage breaker wouldn't have helped with this.
Depends how it's terminated, even with a twist on the nesting material would be still liable to touch it.
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The fuse (old style wire, not circuit breaker) didn't blow. Would have been better if it had. An earth leakage breaker wouldn't have helped with this.
Why not? If their nesting material touches the earth connector/wire as well why wouldn't some earth current start to flow? It's pretty much the same potential as neutral, so all else being equal would attract the same current.
... what earth?
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what earth?
Well I'm assuming with the talk of a theoretical earth leakage breaker he was also talking about theoretical earthed wiring.
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what earth?
Well I'm assuming with the talk of a theoretical earth leakage breaker he was also talking about theoretical earthed wiring.
Earth wiring is not necessary for operation of an RCD.
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this can be solved by using cable glands and junction boxes, but it will cost about 50% more per install (but of course, this is about 0.0000001% of what the house is worth, but people will absolutely flip the FUCK out if you suggest it).
people like to put garbage into their houses for some reason (shredded news paper insulation) rather then proper materials (rockwool) and use ridiclous things like aluminum wiring.
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what earth?
Well I'm assuming with the talk of a theoretical earth leakage breaker he was also talking about theoretical earthed wiring.
Earth wiring is not necessary for operation of an RCD.
But an external path to earth is, and with no electrical box or any sort of metalwork, let alone a ground wire, I don't see how that would be possible.
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Earth wiring isn't necessary, in the worst case a human will do the trick (that's why it's always good yo have a nice new sensitive RCD) in this case there was no way the RCD would trip with a switched phase or neutral and no nearby wood damp enough to conduct to ground.
Would have needed a non-insulated earth connection just resting nearby.
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Can confirm that termites love soft wood. Years ago we cut down a turpentine tree, and left it as logs at the boundary, yo control soil erosion. Years later those turpentine logs were absolutely unscathed by termites, but the pine logs next to them, despite being 4 times the diameter, were just a bark shell over termitories.
Guy, a simple way to fix the termites is to go to the industrial suppliers store near you and buy a few big bags of Borax, sold as a laundry brightener. Then simply either dig into the soil around the house, or make a near saturated solution to pour around the foundations lavishly. Termites do not like that at all, along with roaches and pretty much every other insect.
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Borax or get some ants. They simply loooove :P them some termites. Now what to do about the ants?
I only use AFC Flex cable in metal boxes. I've seen Romex go up in flames for a multitude of reasons, handyman - homeowner bodges, mice etc. Nothing is perfect, but for what we all do here, a pound of prevention....
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Certainly, in WA, even 100+ year old houses have been rewired with PVC over the many years since then.
I had occasion to climb around in the roof of a "Federation" era house, & came across some "tramline" type wiring.(bare copper wire supported by porcelain standoff insulators).
It had long ago been disconnected, & the wiring in use was all PVC.
An interesting sidelight ---someone in the past had put a TV antenna inside the roof, which does work OK with tiles, but not with a metal roof like this house had.
The antenna was resting across both sides of the old "tramline' wiring, so it's just as well it had been replaced.
That sounds like what's known in the states as "knob and tube" wiring. I've seen it in a few old houses (even still in use in a few lighting circuits at a friend's 1920s-ish house). The knobs are porcelain insulators used to support the wire, and hold it where turns were made, and the tubes were porcelain sleeves with larger heads at one end the were fitted in a hole wherever the wiring passed through a rafter, joist or wall stud. I'm happy that I can just pull a single cable with hot, neutral and ground all in one these days. MUCH easier!
K&T still had insulation over the wires. I've never seen it with uninsulated bare copper wires.
If you're curious about the history of electrical wiring, archive.org has some good old books about it.
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Certainly, in WA, even 100+ year old houses have been rewired with PVC over the many years since then.
I had occasion to climb around in the roof of a "Federation" era house, & came across some "tramline" type wiring.(bare copper wire supported by porcelain standoff insulators).
It had long ago been disconnected, & the wiring in use was all PVC.
An interesting sidelight ---someone in the past had put a TV antenna inside the roof, which does work OK with tiles, but not with a metal roof like this house had.
The antenna was resting across both sides of the old "tramline' wiring, so it's just as well it had been replaced.
That sounds like what's known in the states as "knob and tube" wiring. I've seen it in a few old houses (even still in use in a few lighting circuits at a friend's 1920s-ish house). The knobs are porcelain insulators used to support the wire, and hold it where turns were made, and the tubes were porcelain sleeves with larger heads at one end the were fitted in a hole wherever the wiring passed through a rafter, joist or wall stud. I'm happy that I can just pull a single cable with hot, neutral and ground all in one these days. MUCH easier!
K&T still had insulation over the wires. I've never seen it with uninsulated bare copper wires.
If you're curious about the history of electrical wiring, archive.org has some good old books about it.
D'oh!! Good catch - I somehow missed that he said BARE wires. Yes, the K&T I've seen and read about was insulated. Uninsulated wire carrying mains through the walls and in the attic seems a bit alarming to me. Once again, vastly different standards in different countries.
-Pat
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what earth?
Well I'm assuming with the talk of a theoretical earth leakage breaker he was also talking about theoretical earthed wiring.
Earth wiring is not necessary for operation of an RCD.
But an external path to earth is, and with no electrical box or any sort of metalwork, let alone a ground wire, I don't see how that would be possible.
You do realize that this “impossible” alternate path to earth is literally the exact raison d’être why RCDs exist? Whether an earth wire is present or not is actually not relevant to the RCD’s functioning. (The earth wire does, in grounded appliances, provide protection against some other failure modes.)
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what earth?
Well I'm assuming with the talk of a theoretical earth leakage breaker he was also talking about theoretical earthed wiring.
Earth wiring is not necessary for operation of an RCD.
But an external path to earth is, and with no electrical box or any sort of metalwork, let alone a ground wire, I don't see how that would be possible.
Exactly. This is a light switch wiring. Two wires, one Active, the other to the light. When they are shorted, light comes on. There's no Earth wire, and even if bare conductors touch the wall woodwork, it's unlikely to draw enough current to ground (the actual ground on which the house sits) to trip an RCD. The 'slow burn' effect is due to the light being in series with the current path. Hence no thermal runaway to arcing, and the whole charred mess staying just below ignition temperature for wood. Luckily.
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Certainly, in WA, even 100+ year old houses have been rewired with PVC over the many years since then.
I had occasion to climb around in the roof of a "Federation" era house, & came across some "tramline" type wiring.(bare copper wire supported by porcelain standoff insulators).
It had long ago been disconnected, & the wiring in use was all PVC.
An interesting sidelight ---someone in the past had put a TV antenna inside the roof, which does work OK with tiles, but not with a metal roof like this house had.
The antenna was resting across both sides of the old "tramline' wiring, so it's just as well it had been replaced.
That sounds like what's known in the states as "knob and tube" wiring. I've seen it in a few old houses (even still in use in a few lighting circuits at a friend's 1920s-ish house). The knobs are porcelain insulators used to support the wire, and hold it where turns were made, and the tubes were porcelain sleeves with larger heads at one end the were fitted in a hole wherever the wiring passed through a rafter, joist or wall stud. I'm happy that I can just pull a single cable with hot, neutral and ground all in one these days. MUCH easier!
K&T still had insulation over the wires. I've never seen it with uninsulated bare copper wires.
If you're curious about the history of electrical wiring, archive.org has some good old books about it.
D'oh!! Good catch - I somehow missed that he said BARE wires. Yes, the K&T I've seen and read about was insulated. Uninsulated wire carrying mains through the walls and in the attic seems a bit alarming to me. Once again, vastly different standards in different countries.
-Pat
The earlg Edison systems used bare wire even here, but that soon stopped after the introduction of the NEC in the 1890s. So if you see bare wires here it's a Victorian era DC system.
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For completeness - I cut holes through the inner of the double brick wall foundation under the bathroom concrete slab. Expecting the termite trail between ground and the timberwork to be in there. And it was.
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I don't see any metal shielding to keep the termites from wanting to crawl onto the wood, or maybe it's just not zoomed up in that area. Looks like that pipe doesn't have it though..
https://en.wikipedia.org/wiki/Termite_shield
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Well, I was looking for a thread with termites. Here I can add that I have termite shields, but they don't work. In general, termites appear in the house in the warm season, but they do not just appear in my house, but colonies are fleeing from somewhere. I even read faq about termite control (http://www.bugszapper.com/faq-about-termite-control-a-synopsis/) and found out that that a typical termite inspection can cost between $ 65 and $ 100 and is usually accompanied by a report on wood destruction by insects. Moreover, they often do not guarantee the effectiveness of spot treatments, as termites can feed in many different directions.