The case of the mysterious cable arcing

Reece sent this plug-in thermostat and extension cable after an incident when he plugged it in and the cable immediately started burning in the vicinity of the sensor cable.
Quite interesting analysis of the cable damage with bonus teardown of the thermostat.
In hindsight, the fault may have been initiated by the core being partially cut through, as indicated by the outer damage on the cable.
If you enjoy these videos you can help support the channel with a dollar for coffee, cookies and random gadgets for disassembly at:-
www.bigclive.com/coffee.htm
This also keeps the channel independent of KZbin's advertising algorithms allowing it to be a bit more dangerous and naughty.
#ElectronicsCreators

[@HiddenWindshield]

I was once trying to trace an audio (computer speaker) cable through a rat's nest of wires somebody had made behind their desk. As it turns out, "rat's nest" was more accurate that I'd have liked, because some rodent or other had chewed through the insulation of the computer's power cable. The copper was exposed but not cut through, so the cable still worked, until I pushed it aside and the copper brushed up against the bare metal desk leg. Loud bang, bright flash, breaker tripped. Fortunately, the only casualties were the cable itself, a scorch mark on the desk, and a... well, let's just say "mark" in my pants.

[@jonathan_herr]

Front or rear mark?

[@HiddenWindshield]

@@jonathan_herr I think I'll leave the answer to that up to your imagination.

[@harrickvharrick3957]

One actually would think a thing like that would happen way too fast for the body to react by leaving ANY mark !

[@em0_tion]

@@jonathan_herr There's a reason why the live wire is BROWN. 😂

[@HiddenWindshield]

@@harrickvharrick3957 Well, I *did* survive, after all. I might not have mentioned that. In fact, I didn't get shocked myself at all, it was just the sudden flash and bang six inches from my hand.

[@josephking6515]

That drawing looks like someone who is *very* surprised that their hat has caught on fire. 😲

[@mikethedigitaldoctorjarvis]

🤣

[@blankroomsoup666]

This comment made my day 😂😂

[@bobroberts2371]

Or maybe the start of a DEVO vid.

[@erg0centric]

Clive's beard has turned green.

[@lancecullen77]

Rather my hat catch fire than my trousers.

[@someguy2741]

It would be far more exciting if the exploration were done whilst it is still plugged in. Its like a BigClive version of the Operation game :p

[@asmolbean9300]

But when it buzzes, you die.

[@jyvben1520]

that is more like electroboom's job

[@southilgurl2003]

Came looking for electroboom comment, was not disappointed!

[@samuelbeckett4632]

Ah different times.... when it was acceptable to take turns "probing a hospital patient".

[@someguy2741]

@@asmolbean9300 Its far too safe being a kid nowadays. Maybe the Operation game should come in a mains powered version :p

[@Azlehria]

I once had the joy of finding such a fault the hard way, unintentionally. There weren't any visual or functional issues, I just wanted to move the cord. Unfortunately I happened to pick it up at precisely the location of the insulation failure, with the drooping cable pulling the wire apart. My palm and several fingers were in direct contact with the arc for several seconds, with both the cable _and my hand_ catching fire at some point. Unfortunately I'd been using my strong hand, since it didn't actually _work_ for several days and was weak and awkward for some weeks afterward. These days my hand works just fine, and in the end there wasn't even any scarring. I've been much more cautious around extensions since then, though.

[@Speeder84XL]

I had a similar thing happen to me. In my case, it was a hot air gun that seemed to have a bad connection inside - but it turned out to be a broken lead in the cable instead (the broken ends of the lead was just barely touching inside the cable, making intermittent contact). When I moved the cable, an arc appeared and burned thru the insulation almost instantly - right where I was holding it. I didn't burn my hand so bad that I had problem using it afterward. But I was only in contact with the arc a second or so at most and that was still enough to burn thru the skin and leave a small open wound at the point in contact with the arc and some burned skin on 2 fingers

[@bobroberts2371]

Another consideration. Over on the Curious marc channel, they had an issue with wire wrap that was actually copper plated aluminum. The wire fractured internally and lost continuity but no arc. I've been seeing China wire that is more towards brass than copper. This seems to be on the brittle side.

[@sjames5027]

A Scary Movie strong hand?

[@mungtor]

My grandfather was a carpenter, so that blade has always been what goes in a "sheetrock knife". I still call it that, interchangeably with "utility knife" depending on who I'm talking to.

[@dashcamandy2242]

My grandfather was a plumber, he called it a "wallboard knife."

[@LachskoenigIV]

Its obviously a Teppichmesser

[@hiscifi2986]

Stanley Knife in the UK, and the entertainments industry.

[@ebnertra0004]

I've heard 'box cutter' and 'utility knife' for the most part

[@stevenwright901]

@@andrew_koala2974 angry koala

[@technic550]

That has been arcing for a while I would say, the heat damage on the insulation has probably been caused by a prolonged fault. Probably bent very tight at some point, lost a few strands, then loaded with a heater. Moving the the lead to plug in the new stat would explain the coincidence

[@ianc4901]

That's not a 13 amp cable, it looks exactly like it had been damaged, maybe a few strands of the inner wire were broken and it was then connected to a 13 amp load.

[@CoolSteve08]

@@ianc4901 yup, 0.75mm² cable is rated at 6A max, allowed fuse values are either 3A or 5A. the plug does say it has a 5A fuse in, but that's not necessarily what's actually inside it. Also a 5A fuse could likely take 8A almost indefinitely, so even though it's rated 5A that doesn't mean it will blow at that current.

[@stephenjones9153]

@@CoolSteve08 I agree 👍 I was always taught that standard plug fuses blow at approximately 2.5 times the rated current. So they don't blow with say an initial startup current of a vacuum clean or similar high inrush device. Looks to me that extension lead was not rated for a heater and overloaded. I only use 2.5mm flex cable on my extension leads to any heater and even then if not un-coiled they still get warm.

[@argoneum]

Now that looks suspiciously like a cable with wires made of "a luminum". "A luminum" is an obscure element from China that looks like copper on the surface, but under load of one amp or more makes a flash of light (hence "luminum") and popping noise, while itself disappearing. Had some extension cord marked "16A" on the outer insulation and the plug, and it didn't survive 3A, having very similar effect. It had a strand of super-thin copper-plated aluminium wires. They also made fireworks-like effects when subjected to a flame.

[@hipu]

Fun fact: This material is known by Canadians as Aloo-minimum

[@argoneum]

@@hipu Probably has something to do with telephones (aloo) and mines, who knows :)

[@esecallum]

@@argoneum automatic circuit breaker/fuse?

[@seraphina985]

In and of themselves these are not necessarily a problem but the conductor diameter does need to be larger. For instance at 20A around 2.05mm is sufficient for pure copper cable but copper clad aluminium needs to be closer to 2.58mm which is around a 60% increase in cross section and surface area. This is because aluminium has only about 61% of the conductivity of copper so you need to beef up your conductor my guess is that the Chinese manufacturer cheeped out and omitted that step. By the way I grabbed those numbers from the US specs as I know they allow it in household wiring apparently for a 20A receptacle they allow 12 gauge (2.05mm) for copper and 10 gauge (2.58mm) for copper coated aluminium.

[@km5405]

@@esecallum its a feature! fused power strip (non replacable)

[@johnwilliamson467]

Stanley being a major maker of utility knives in USA you are correct in calling it a Stanley blade .

[@SLEEPYJK]

Stanley is widely used worldwide, not just in the US.

[@ridefast0]

I love the 'hook' type Stanley blades, when I can get them. Great for cable stripping or safer opening of parcels or envelopes.

[@JezCunningham]

@@ridefast0 Intended for carpet cutting I recall…

[@eDoc2020]

No, when the knife caused something dangerous Stanley Black & Decker, Inc. will be first to point out that it was, in fact, a competitor's product.

[@sjames5027]

I thought they were all called Box Cutters over there

[@the123king]

Clive, I've seen chemical reactions dissolve or "melt" both hard plastics and soft cable sheathing in older electronics. There's something in older and/or cheaper cabling that seems to react with other types of plastic, particularly from 80's electronics. It's possible that something in the thermocouple wire has reacted with the PVC insulation on the extension lead, which could have caused the "cutting" effect you mentioned.

[@andrewwhite1793]

Like grommets slowly melt their way through a clear plastic draw. I think its the plasticiser.

[@der.Schtefan]

I have become addicted to your channel and can't stop watching it. I think I dug back 4 years already. This channel is sooo good! Your voice, your jokes, the way how you present stuff, your explanation of electronics, the relatively easy to understand level of electronics, the vast knowledge that you are very eager to share, your versatility when it comes to knowledge, omg, love it.!

[@TopEndSpoonie]

I do love the circuit exploration. Since watching you for a while now, I find that I can now look at a circuit and know what each segment is doing, as soon as I know what the chip is. A realisation that I came to just the other day. Great work Clive, "ya bloods worth bottling." ( to use an old Aussie saying ).

[@MOOGSTINE]

Me too! Big Clive is my favorite youtuber I've learned a world of knowledge from him

[@Abihef]

Can't wait to see you open a printer or synthesizers Indeed learned a lot from him though

[@Hagar76a]

I came across Clive looking for help repairing a CTek charger. I also like watching Dave's repair vids. Bloody legends they are.

[@draconightwalker4964]

ive not heard that saying in years

[@bakedbeings]

@@Abihef At least he'll immediately know what he's not looking at 😂

[@sparkyprojects]

I've had a flex where it looked like the factory had come to the end of the run and spliced (welded) the next piece on before running through the insulation process. Could have been the case here, or stretched as you said. But with that cross cut it could have damaged a few strands, he said he plugged a heater in, which could have created the hotspot with the high current that caused it to break down.

[@cameradoctor205]

I use velcro fasteners to hold the cable roll for this very reason :)

[@tin2001]

I hate using tape on cables... Not because of knives cutting the cable, but because it leaves a disgusting sticky mess if it gets left in a warm/hot place for more than a a few days.

[@etherealrose2139]

I highly doubt a velcro fastener would help in this situation. I took like it was suspended over a corner with weight on the end, cold working the metal. People don't usually move extension cords a lot especially indoors.

[@HappilyHomicidalHooligan]

I use zip ties or a loop of twine if I need to hang the cable for storage...

[@MOOGSTINE]

Big Clive is the best! I've learned a world of knowledge from him. Weither it be history engineering or troubleshooting

[@Slikx666]

When I've been a roadie for bands and we e been packing up the PA system and lights we used cheap electrical tape, it did the job but we never needed to use a knife. For my personal equipment Guitar leads, power leads etc. I use hook and loop straps. They're always attached to the lead so they don't get lost and they last a long time. The other advantage they have is the leads Don't have sticky too left on them. And please don't fold your leads up and tie them into a knot, it just ruins them.

[@Mister_Brown]

a great choice is either gaffer tape (the cloth stuff not the uk name for duct tape) or paper backed velcro made for tying plants to stakes, that stuff is amazing for bundling cables and easily breaks when you want it to

[@squelchstuff]

I think you were mostly correct in the first instance. The outer sheath definitely looks like it had been damaged at some point, although probably only partially cutting the live conductor. If the load was heavy, or has a high inrush, it may have just been enough to burn the remaining conductors as the current heated what is effectively a fuse. Fireworks then ensue. Interesting coincidence with the timer-stat though. Thanks for sharing Clive. [Edit to add] The V shaped cut on the outer sheath looks all the world like it has been trapped under the corner of something heavy at some point.

[@whitesapphire5865]

That reminds me of a cable to one of my space heaters which was nibbled by a rat, or it could have been a mouse. I was nearby at the time, blissfully unaware of the rodent snacking on the lead. There was a loud farting and bubbling sound followed by a plaintive "Ooh, ooh, uh, ooooooooh". I never saw the rodent, but the damage was clear, rather similar to the cable seen here. I suspect young Rodney ran off with his gob full of fire and subsequently keeled over and stiffed out under the shed floor. The point being that the burning and damage looked almost identical to that in the cable you just post mortem'd. I remember my granddad running his hand along an extension lead when I was kid, and he found a nick in the sheath, or more to the point, the nick found him! This is also why we should inspect cables and leads quite regularly for damage.

[@robinwells8879]

I wonder if frequent coiling/uncoiling of the cable has caused what we call a z kink where the copper conductor gets stretched beyond its elastic limit and lengthens but the insulation remains elastic and the excess length forms a kink. These then fail due to fatigue cracking and a resistance fault leads to arcing and the eventual failure as it vaporises the conductor until an open circuit is made. This often happens when bend restrictors fail. I had this happen inside the palm of my hand whilst ironing with a worn cable. Ouch!

[@bobroberts2371]

Another consideration. Over on the Curious marc channel, they had an issue with wire wrap that was actually copper plated aluminum. The wire fractured internally and lost continuity but no arc. I've been seeing China wire that is more towards brass than copper. This seems to be on the brittle side.

[@hauptmannoffensichtlich2312]

I love it that you showed the cause of the flaw very well, noted the whole video was way too short and promptly proceeded to explore that thermostat instead.

[@brentengelhart5]

You are excellent Clive! Educational & entertaining. A wonderful, comforting KZbin friend!

[@SusanAmberBruce]

Very well explained, there is no substitute for experience as you have demonstrated multiple times in your videos

[@jamesplotkin4674]

I've read all the comments, so far (165 of them) and the vast majority don't mention the cut into the outer sleeve as if the tension on one wire is all that happened. To me, this failure isn't from the cable being pulled at all. It's the knife cut. The fact that the hot lead was "shorter" is most likely from the destruction from the arcing.

[@thewhitefalcon8539]

Assuming that it was a knife cut.

[@cambridgemart2075]

But what did it arc to? The neutral wire insulation was still intact.

[@jamesplotkin4674]

@@cambridgemart2075 It was parted by the knife cut and that, alone, causes an arc due to barely making contact. It's a guess.

[@gamesmithoz]

Since it's a thermostat and it's the UK it was most likely connected to a heater....

[@StudSupreme]

I envy you your skills. You bring out the beauty in old, basic electronic systems. There's art in it, and you reveal it. It's extremely interesting to watch these vids.

[@nightw4tchman]

As an audio tech, who wants to avoid wasting LX tape (ideally I'd like to got fully velcro) at my venue that first bit is a great lesson in wastage management and how something simple can go horribly wrong. I've had to cut LX tape before with my Leatherman and always try to avoid cutting towards the cable, but not all of us do.

[@colinmiles1052]

Big Clive, I understood about 10% of that but enjoyed 100% of it! Thanks.

[@muppetpaster]

2:30 We tend to call all Stanley-like bladed knifes a Stanley-knife in Holland ,even them breakable blades..(also the tiny ones)

[@okaro6595]

In Finland we call them carpet knives.

[@richardhalliday6469]

The generic name is Utility Knife Blade.

[@chrisnoname2725]

Same in Australia

[@mina47879]

Same here in Australia

[@olik136]

@@okaro6595 also a carpet knife in Germany

[@nigeljohnson9820]

I have seen examples of chemical interaction between electrical cables. Some have a plasticiser in their chemical makeup, that reacts with other cables. The offending cables become sticky and melt, sometimes exposing the underlying conductors. On one occation, a cable was placed on a gloss painted window sill, the cable insulation reacted with the paint, gluing the cable to itself and to the surface. A similar problem was observed with a painted book shelf. It is common practice to wrap the low voltage lead of a battery charger plug around the plug for storage. Sometimes there is an interaction between the plastic of the charger case and the cable, again sticking the two together, damaging both. My first reaction,when viewing the video, was that the black probe lead might have reacted with the mains cable, exposing the conductors, resulting in a short. Your explanation is consistent with the evidence, but the problem of chemical interaction between cables does exist, and is more common with the black cables. Thinking about this video, an interesting experiment might be to wrap the black probe wire around the white mains lead, just to see if there is a chemical reaction between the two. ( by the way, I recall a recent tear down review of an optical fire alarm, but this seems to have been deleted from your site, or did I dream the whole thing?)

[@ferrumignis]

_"Some have a plasticiser in their chemical makeup"_ All PVC insulation for cables has plasticiser in it, but the older plasticisers were not chemically bound to the polymer and it would leach out causing the symptoms you describe.

[@nigeljohnson9820]

@@ferrumignis I have found this problem very common with Chinese imports. I have a high speed drilling and cutting tool, the plastic/ rubber case of which has become very sticky. The problem is also shown by an electronic hand held microscope and a led illuminated magnifying glass. The common feature, is that all have a rubber plastic case, which is obviously intended to improve grip. But I also have a set of headphones that were stored in a polythene plastic bag, when this was opened after a few months, the lead and jack plug had melted and amalgamated into a gooey mess. Attempts to separate the cable, stripped it back to the conductors. I managed to repair the drill tool, microscope and magnifying glass. It was necessary to strip the products down to its case and electronics. The cases were then washed in a concentrated solution of sodium bicarbonate, then washed with clean water, and then air dried before reassembly. I understand that when the plastic decomposes, it becomes wet with a hydrochloric acid solution, it was remiss of me not to check this claim with litmus paper, but I can confirm that the residue is very irritate to the skin, producing a burning sensation. I have yet to discover if the sodium bicarbonate treatment is a permanent fix, but it does restore the plastic surface to its original dry condition from some time.

[@marquisdemoo1792]

In the military we had 10pr cables for telephony, which meant there was 48V between the A and B legs. These cables entered communication vehicles via a bulkhead connector on the skin of the vehicle. For most of my tour in a field unit in Germany we were plagued with noisy crackly telephone circuits which we put down to the multiplex equipment in the vehicles. It was only just before the whole system was replaced did I discover these bulkhead connectors had a rubber separator in them and the majority of these had little carbon tracks burnt into them between the the A and B legs. We then tested them all with a Mega and replaced those which were faulty, which was most of them, and deployed one last time with quiet telephone circuits. I should add these couplers being on the outside of vehicles, that were rarely garaged, meant the couplers, although sealed, were inevitably damp. Another aspect was that the cables themselves were maintained by Linemen who were trained to and did routinely test their cables with a Mega, which would show any break down, whereas the vehicles were maintained by technicians who were not trained to do so. If they were to test the wiring between the skin of the vehicles and the internal equipment they would probably use an AVO (multimeter) at low voltage rather than a Mega at high voltage.

[@rickbates9232]

Love your electronics videos, thanks Clive.

[@marcse7en]

Hi Big Clive! ...... Little Clive here! 👍😂 I'm NOT in the entertainment industry, but for many years, I've routinely checked cables for damage by pulling them through my hands, and feeling for any damage to the ⚡ insulation!

[@Weissenschenkel]

People yanking off appliances' cables like my mother (a lady Born in the 1940's) will eventually face the same issues, unless it's a rugged coaxial cable. When I told her to do not yank the cables she started to pull the plugs with appliances like washing machines and other induction loads while draining current, melting not only the plugs but the power outlets themselves, due to arching. I asked her why she wasn't ever switching off the appliances. She had set one extension cord and one outlet on fire. Gladly the breaker switched off and avoided something worse to happen. She also plugged her vacuum cleaner in my no-break outlet and blew a fuse, rendering my file server unusable while I was trying to remotely connect from a client. Sigh...

[@OlaMagnusLie]

When I worked as an electrician I was mounting outlets. I don't know the English technical term, but when I prepared the installation cable, first I removed the white sheath and when I was about to remove the insulation a good 15cm of copper came with it. I checked this up and it happens from time to time that the copper breaks in the production line, and if you're lucky enough it produces an air gap large enough for the cable to be faulty. …If you're unlucky, however, the air gap is small enough for the electricity to arc over it for a while…

[@James2210]

Removing the insulation from the wire is called stripping

[@OlaMagnusLie]

What's it called when you remove the copper from the insulation instead? Aha! Got you!

[@8bitwiz_]

I had been rigging up XLR adaptors for an Ethernet cable tester one day, and went to test every XLR wire I could find. One of them was a second-hand cable that showed a short from a signal wire to the shield ground. It turned out that one of the insulated conductors had kinks in it during manufacturing, and in a few places the insulation got rubbed off at the kink. The exposed wire then shorted with the bare shield wires around it. I was able to chop the bad bit out and add two spare connectors. So while improbable, it is definitely possible to have wires faulty when manufactured.

[@acmefixer1]

Thanks for the grand tour, Clive - very informative. I didn't hear anything about the brown conductor's size or if it was copper. I've had to measure a strand or two and count the number of strands and calculate the gauge of the conductor, to be dismayed to find that the conductor is undersized for the amount of current that it must carry. And I've been very disappointed to find that the conductors attract a magnet, showing that they're not pure copper! 😱😱 Another thing to despise is that zebra strip.

[@BjornV78]

3:45 That's why they invented the arc-fault circuit interrupter (AFCI) or arc-fault detection device (AFDD), because damage to a electrical cable can cause fire long before a circuitbreaker trips.

[@treelineresearch3387]

I've heard "Stanley knife" (and indeed you can buy Stanley brand ones) in the states, it's not as common as "utility knife" or "box cutter" though.

[@Magisktification]

So you call loose blades utility knife and box cutter? That sounds so weird to me 🤔

[@dogwalker666]

Technically it's a utility knife just Stanley cornered the market in the UK, just as Hoover did with vaccume cleaners, however a box cutter is a completely different device with a protection arm underneath to protect the contents,

[@kasuraga]

weird. in the states ive mostly heard box cutter at work. never a stanley knife

I would just call it a box cutter too, yeah

[@funkyflashfive]

@@Magisktification The loose blade would be called a utility knife blade or a box cutter blade. I've used a stanly brand one, but never heard it as a generic

[@kevinmartin7760]

In the stage theatre where I used to work, we tied the cables with short pieces of braided cotton cord (about 1/4" thick). You would coil the cable (in a manner that did not fight its natural twist), plug it into itself, wind the cotton cord around it once or twice, and tie with a reef knot. When the cables were in use, the ties stayed on the cart where the cables are be stored.

[@8bitwiz_]

If they can be plugged into themselves (like XLR), you can keep them on those big plastic power cord reels. This is especially nice with 6-10 foot lengths that otherwise would be too short to stay looped.

[@Darieee]

super cool .. fault analysis is the best

[@jbuchana]

My father used to call them box knives, a friend called them carpet knives, but another friend said he was crazy, a carpet knife is something else entirely. I usually go with box knife, but I've heard Stanley knife used as well. The one sitting on my bench is a genuine Stanley brand, the one out in the garage is a Craftsman, same blade. This is in Indiana, in the US BTW.

[@realmadstupid]

Utility knife is what they are usually called, including the ones made by Stanley. I don't know if Stanley invented the first utility knife but they did patent a retractable utility knife in 1963 simply titled "utility knife"

[@Ureallydontknow]

Excellent video 🙏

[@70mmbobbyj]

As someone who has worked in the UK cable manufacturing industry the white outer covering is the sheath and the inner conductor covering is called the insulation

[@mscir]

Great class, thank you.

[@davidtexmex1616]

Nice work detective Clive 🕵🏻‍♂️

[@ranger175a2w]

Thanks again Clive.

[@UpLateGeek]

I had a slightly different thing happen to an Ethernet cable when I was pulling through another Ethernet cable under the floor of a our data centre at work. The outer jacket was pretty aggressively conformed to the twists of the pairs inside, so it was particularly ribbed (For her pleasure? Because it wasn't for me!). When I pulled it through, it happened to run over a perpendicular cable, which evidently didn't have a very tough jacket, because it gouged right through it and then went through the insulation on the pairs. Only found out about it later when IT started complaining about a server becoming unreliable. Found the gouge when I was tracing out the connection from the server to the switch, so obviously I replaced it immediately. When I checked the port logs and stats, it was constantly going down and up, and lots of packet errors. The problems went away with the new cable. Needless to say we switched to a less aggressive brand of cable.

[@linuxgreybeard9945]

Excellent example of why the heavy duty rubber cable protectors are essential in an office environment. Furniture, desk feet, chair castors etc. squashing power cables have probably resulted in more premature cable failures than stiletto heels or indeed Stanley knives.

[@laminatedsamurai]

Typically called a 'utility knife' here in the US, with Stanley being only one of a variety of brands, but by far one of the oldest still readily available.

[@crimsonhalo13]

Reminds me of the time I got to replace a defective 120V dryer plug after the thing arced internally and tripped a breaker. After taking it apart, I came to learn that the brass prongs and copper wire inside the plug had corroded and generated colourful green substances that had grown over time and eventually bridged contacts, causing the fault. (It was a good lesson in why one should always inspect every square centimeter of secondhand appliances, inside and out.)

[@leonpijpers7327]

At the picture of the cable (1:30) it looks like the white vertical damage, could be caused by some imperfection in the plastic, in combination with bending it, could have damiged the white insulation and the brown insulation of the Phase L wire. As you said a bit of moisture could have helped a bit too. Later in the video it shows one of the thermistor wires is connected to the ground of the secondary circuit. The interresting part is how this is connected to the Neutral wire, as that what has probably made the missing link from Live to Neutral. In the cable you see there is almost no damage on the blue wire, telling me that is not the way the current went to Neutral. After the first spark from the brown cable to the 0V of the thermistor, in combination with probably a heavy load (some heating device) on the output socket of the device, made the current to high for the damaged brown wire. It must have been disturbing and exciting to see the plasma balls when that was happening. Possible the Neutral is connected directly to the Ground of the 8051 microcontroller, I cant see any safety cap, the transformer might have connected the ground side of the Neutral input ground connected to the Ground of the microcontroller and the metal outside of the thermistor. This is normally not a problem because of the polarised UK plugs (it would be a big problem with dutch unpolorised plugs). so to finish the investigagion, check if the transformer has the 2 different ground connection in the datasheet schematic at 10:50 connected would be conclusive.. great video and investigation of an exciting problem Clive!

[@tonythemadbrit9479]

The extension cable seems very old based on how the insulation broke into pieces. As others have said, probably an internal breakage of several strands in the live conductor caused by bending, which overheated the remaining strands when current flowed, causing it to open circuit. Current then continued to flow through the resultant plasma, which is why a fuse or breaker would remain closed as the current was the same or less than before the fault. Eventually the conductor ends melted until the gap between the ends became too far to sustain an arc. Maybe strip the other conductors at the same point to look for more broken strands?

[@gianlucalocri]

Yes, I'm of the same idea! It happened to me with an old vacuum cleaner. The cable was stressed from the winding cycle over the years and some wires eventually broke somewhere, then the weakest point overheated and boom! Also, the overheated plastic became brutal and prone to making the sort of clean break as seen in the photo.

[@r0cketplumber]

A much simpler mechanism may be that the live wire was cut most of the way through, then when the resistance heater load was applied, the last strand overheated and blew, causing tracking *across the break* with an impressive arc and heating that caused the additional bonding to the neutral wire. The cable wasn't stretched, the hot lead had a section vaporized- that's why it's now shorter than the others.

[@MyIronman8]

what an great video keep the good work up loved it

[@WineScrounger]

For years now I’ve been making rope rings for hanging up cables and hoses. Just take about five feet of light rope, splice it end to end and you can hitch it through itself around a bundle of cable (and many other things). It is strong but comes off easily and can’t damage cables. Also reusable.

[@mrfrenzy.]

Old fanbelts are also a good loop to hang long cables and hoses.

[@Scodiddly]

Good for at home, but generally in the entertainment industry all the cables get thrown into a trunk which is pushed onto a truck for delivery to the next show. Where I work we use hook & loop cable ties with our logo.

[@andrewwhite1793]

Have you seen a Dyneema rope shackle? Same idea, just on steroids 😃

[@bhoiiii]

I call it a razor knife. I’m in the South of the US. Yet I fully understand what you mean by a Stanley knife.

[@talideon]

I too (Irish) would call it a Stanley knife, though apparently the generic term is "utility knife". To be fair to the 8051, it's aged pretty well as an ISA, all things considered, and more modern clones are really fast and efficient. It's really good at anything that involves a lot of bit twiddling.

[@BritishBeachcomber]

Probably the only YT channel I can identify 100% just from the thumbnail.

[@Equiluxe1]

I have had wires in the past where there was a discontinuity in the conductor from new. I used to manufacture trailers and one time I wired up the lights and nothing worked in the end I traced it to the white return/ ground/earth wire having no copper for a distance of 8 mm. In order find this I had to strip the entire loom of 7 core cable down. Since then I have always been on the look out and have found such faults on many other new cables including flat twin and earth, I think the problem occurs during the manufacture where one wire is joined onto the next during the calendaring process.

[@ahettinger525]

ultimately, the thermostat looks like a pretty nice design! Not what I'm used to see here :D

[@joepollard8755]

A good example of where an AFDD would be useful. A series arc in an active won't trip the overcurrent or residual current protection (unless the ensuing damage eventually gets the neutral or earth conductors involved), but an AFDD can detect the arc by monitoring the AC waveform

[@mallow173]

Perfect explanation Clive!! Thankfully he was in proximity to it when the arcing event happened and it wasnt in proximity to other more combustible materials! Got a question...do you suppose the load was more than the cable was capable of handling? How many times have you seen that as an example?? Is it possibly another case of Amazon junk? Very nicely done sir!

[@LoftechUK]

Nice work

[@mikefellhauer3350]

I DISAGREE with the initial cause. You stated the black thermostat cable was lying on the extension cord. One thing I've seen is when mixed plastics come in contact with each other that it causes a melting reaction even if there was nothing energized! The "nick" in the white chord looks like this is what happened! I know this is an unbelievable theory, but I once had a backlit keyboard I wasn't using...so I wrapped the keyboard cable around the keyboard and put it in the cupboard. Months later when I needed the keyboard I unwrapped the keyboard cable and the keys looked like they had melted where the cable had come in contact with them. The keyboard was never energized during the storage time, and it was never near a heat source. Yet the keyboard cable "melted" the keys just by coming into contact with them over time. In your case there could be another factor at play, EMF between the two cables...and the extension cable paid the price because it was a softer rubber.

[@jasonkuehl639]

A few years back, when Midnight was a pup with those razor sharp milk teeth, he bit one of my extension cords. I used it around the shop for several months, never noticing the damage. I finished a small project using that cord, and my son wanted to use it for the electric mower in our small garden. Soon as the mower started up, there was a loud pop and the breaker for that circuit tripped. Turns out the little pupper bit through the insulation on the live and neutral, but through all the use in my shop they hadn't shorted together. After a quick inspection, I found 3 more places he had bit! All I can say is it's a good thing it wasn't plugged in when he decided the bright yellow 50 foot 12/3 cord was a chew toy! 😬

[@tin2001]

My dog chewed through a live cable. The 240v didn't apparently worry him too much. It was a cable running a fountain pump, and had one of those plug in RCDs on the input end, so it tripped that instead of blowing the fuses. He did it multiple times over a few weeks before we burried the cable in conduit and switched to 12v solar instead of mains.

[@jasonkuehl639]

@@tin2001 I guess chewing on wiring must be very satisfying to them, every dog I've had has done that as a puppy, and one has done it her entire life. Good thing there's RCDs and GFIs, the quick action of them has probably saved many kids (furry, human, or adult kids) from an unpleasant jolt. Midnight's 2 years old now and I'm still finding cables he bit into or completely through as a pup! I swear he probably bit a few of them and thought it was just spicy spaghetti, though. 😆

[@Agent24Electronics]

I've always heard Stanley Knife over here in New Zealand, referring to any such craft/hobby knife with replaceable/snap-off blades, of a certain size. The tiny pencil style knives with scalpel size blades are not.

[@Jamesimagine]

The tiny ones are usually called 'X-Acto' knives in the US. 'X-Acto' is a brand name like Stanley, the pencil thin 'X-Acto' style knife is usually called a craft knife generically.

[@RobertHart]

I've been running a repair cafe in Adelaide Australia, and have noticed many appliances have broken conductors inside the sheath. When bending the lead it makes and breaks a connection with no external evidence there is a fault, so just replace the power lead. This is not so dangerous with low power devices, but things that are powering more amps like heaters, hair driers and blender such faults can result in something more sparky, burnny distructive!

[@ToolTimeToday]

as good as your video was to watch and find out what's gone on with the short in the cable/flex. I'm curious as to what knife that is you have in the video as well as the place t oget myself one. ? pls ?

[@NicksStuff]

Have you tested the continuity between the thermistor's *case* and ground/neutral? (Maybe the arcing was between the live wire and the thermistor?)

[@barrieshepherd7694]

I've had a very similar thing happen, single broken wire causing arc, on a couple of IEC mains leads with 'chinese copper' wire. I put it down to poor manufacturing and excessive bending in the packaging department. Although apparently not in this case I wonder if the absence of chalk in the cheaper cable construction leads to high friction between the wires so they don't slide against each other so one just takes strain and eventually breaks. In one case it was the earth wire that had broken so no arc just, fortunately, a hum on the amplifier which draw my attention to the issue.

[@soundmangaz6833]

I repair Henry vacuums for a cleaning company and I see this problem a lot. Normally near the plug or sometimes elsewhere in the cable. Caused by the cable being strained often, being trapped under doors and generally having a hard life.

[@thisisyourcaptainspeaking2259]

Reminds me of the time my ham radio antenna guy-wire broke and the antenna fell over, there was a burned section about every 18ft.

[@misamsung6191]

Perhaps it is a UK thing or an entertainment industry but here in Canada I can't say in my 35 years of working in electronics that I've ever seen anyone using tape to to bundle up cables. I have used Velcro cable ties to bundle cables or actually made a knot on long extension cords. Love the show

[@jacobpegher1744]

Entertainment industry thing

[@lourias]

Big Clive, what brand of tools do you have? Or. Where did you purchase them? I am looking for hand tools with large grips, but I am in America, and I do not seem to be able to find them. Any suggestions? Thank you.

[@TimHollingworth]

It looks exactly like a cable extension I once used for a soldering iron. The hot iron burnt through the plastic of the sheath and the live cable and shorted to ground through the iron. A bang ensued blowing the fuse and the live wire.

[@MOOGSTINE]

Your extention cords are cool! Nothing like they have here in the states.

[@thedukeofweasels6870]

in the states it's commonly called an exacto knife or a box cutter. I think Stanley knife might be used occasionally or at least everybody would know what she means since Stanley most of the knives people use these days or Stanley brand

[@orijimi]

Utility knife tends to be the term here in the PNW.

[@Chris_Grossman]

The original blade design was by stanley. The patents expired and the same style is made by many

[@thedukeofweasels6870]

@@Chris_Grossman I didn't know this, thank you

[@chrisred87]

I electrocuted myself on a building site because of a faulty cable. It was wet and I was coiling it up whilst it was plugged in, I got a shock, yelled out and tried to drop the cable as I let it go I got another shock yelled again in a higher pitch and tried to drop it again. This happened about 5 times with my voice getting successively higher untill I managed to drop the cable. Turned out I'd blown power to the entire site. Inspecting the cable I saw a very fine slice in the insulation. I was totally fine and I learnt a valuable lesson!

[@hempev]

Why is there a 0ohm resistor instead of just a connection? Would it be used for an optional resistance?

[@COBARHORSE1]

That's so the automated pick and place machine can be used. A wire link would need to be placed by another machine.

[@Groobl]

The spark plug wires on my car had a similar problem. They were close but not nearly touching the exhaust manifold. Electricity was arcing straight through the jacket and causing misfires, but only after the engine bay temperature reached higher levels after some time of use. The cable didn't noticable melt, but the jacket became crumbly at the arc point. I only noticed (the problem, that is - the misfires were obvious) after opening the engine bay at night and witnessing the brief blue glow.

[@etherealrose2139]

My initial thought, if you just looked at the cable, you'd see it looked bent, like it's been folded multiple times thereby cold working the metal making it more brittle. Probably hanging off a table or shelf right at that point and it just so happens when they plugged it in that time the strands finally broke or separated creating an air gap and an arc. Doesn't have to be a high load plugged in just a constant load as it continually arcs and the plasma heats up melting the insulation. You keep mentioning the entertaient industry for some reason but a cheap thermometer like that seems to suggest it was used in domestic use... I bet that cord never moved from the receptacle it was plugged into. Only the end was continually moved and weight hanging off the end over a corner bending that wire over and over. In fact, you should have cut open the neutral and ground to see the integrity of the copper at that exact point.

[@joels7605]

In the early 2000s I used to work at a computer repair shop in Canada. We would regularly see computers that had ROASTED the cable to the wall. The entire length of the cable would be melted and crispy. They always had one thing in common. Before switchmode power supplies were the norm a common thing to find in Canadian houses was a wall outlet that was connected to a triac dimmer switch. So you could plug a lamp in and control it with a dimmer. Great. Plug a big switchmode power supply into that and it's a recipe for disaster. If you turn the dimmer down the power supply will adjust and continue to pull more and more current until it would literally melt the wire. I think those nasty dimmer wired outlets have mostly been removed.

[@12villages]

I once came across a two pin plastic plug that shocked me. I took a neon tester and ran it over the plastic cover it and started glowing. Turns out, the plastic material used inside electrical fixtures are specific type of plastic. Some local plug maker probably thought that plastic was plastic and moulded a set of plugs using whatever plastic he had around.

[@danbandol1611]

Hi Bigclive. I have a different theory of what happened because I had this issue myself. Temperature probe wire is quite long, imagine you drag the black probe wire against the white. Just like a friction saw. The black one won't have any damage because it acts as a saw. It happened to me unfortunately. Keep up with the entertaining videos. Best Dan

[@bobroberts2371]

Another consideration. Over on the Curious marc channel, they had an issue with wire wrap that was actually copper plated aluminum. The wire fractured internally and lost continuity but no arc. I've been seeing China wire that is more towards brass than copper. This seems to be on the brittle side.

[@NullScar]

I've had the exact same problems with some of my wires in my cold fusion reactor. 👌🏻

[@A2an]

You were spot on, in your first evaluation, just it was only one wire that has ben sliced, and almost over. Then a heavy load and boom it says :)

[@draketungsten74]

Yes, we call them Stanley knives in the US, at least in some parts.

[@omniyambot9876]

Please make more videos with dangerous voltage!

[@dav3yuk]

Lovely well explained theory. Shame the post mortem on the cable wasn't done first. Had a piece of flex go like that myself in a past job. Probably fractured due to repeated winding and unwinding.

[@AintBigAintClever]

Someone in Brecon was badgering the council because the fuses kept popping in her house. Council did nothing until the shed caught fire. Article in the Brecon and Radnor Express, 12th October 2021 after they tried billing the tenant for the fire damage.

[@U014B]

Do people not put courtesy tabs on the tape when they wrap cable?

[@MarkJT1000]

The stretching theory doesn't explain the knife cut across the insulation. My guess is that a cut was made across the cable and partly severed the live conductor. So when a heavy load, like a heater plugged into the thermostat, is connected the remaining intact conductor is overloaded and overheats.

[@d.t.4523]

Don't ya just hate it when you yank a cord and it gets stuck on the door hinge! "Hey, Boss, the forklift ran over your extension cord again!" 👍

[@mikehibbett3301]

8051. I was writing software at Philips for 8051 MCUs in 1989, can't believe people are still writing code for it in 2021!

[@petehiggins33]

Why is that relay at 10:43 rated 16A at 250VAC but only 15A at 125VAC? I tried turning my monitor upside down but it didn't help.

[@PurityVendetta]

After spending an entire summer repairing a skip load of both power distro and signal cables at the UK's biggest PA hire company, I can attest to the fact that cable abuse is a terrible thing. How you can physically tear a military grade connector off the end of a 48 way multicore is beyond me. Then again I do know roadies and riggers. You forgot to mention people who coil cables around their arm. It tends to twist the conductors and put them under tension at the same time.

[@cho4d]

on the subject of cable managing, doing a figure eight with the cable spooling it around your forearm results in an un-tangle-able unit of cable with no sharp bends.

[@Del_UK]

Could the extension lead be rated to 10 Amp load and the item plugged into the extension lead had a higher current draw, which in turn caused the cable to fail? I had similar happen to myself and hence why I check the wiring rating on an extension lead these days. The other thought I have is whether the cable is pure copper or aluminium/copper mix.

[@uwezimmermann5427]

Looking at the jack in the pvc insulation: how sharp are the edges of the metal spades on the power plug? Could the plug have damaged the cable during shipping when/if everything was rolled up tightly in the way one normally gets this stuff shipped from China?

[@markbooth3066]

What a coincidence! While watching this video, I was trying to work out why a moulded IEC C13 cable wasn't working. The fuse was Ok and the outer sheath looked intact, but there was no continuity on either earth or live. I stripped off the outer sheath as you did, and low and behold, a charred and blackened live cable with a tiny sub 1mm blackened spot on the earth cable. Beyond this point, both cores tested for continuity fine. The odd thing here is the intact 3A fuse. I probably last used this cable on an ring without an RCD or circuit breaker, but I'm surprised that even just 3A was enough to burn through a cable which should be rated for the 10A. It's a Fan-jet FJ-013 cable, and searching the web, it seems I'm not the only person to see these cables fail.