Outback shocker left Aussie techie with a secret not worth sharing G'day readers, and welcome once again to The Register's reader-submitted column of cold comfort that we call Who, Me? where you find out that everyone – even clever clogs like you – makes mistakes. This week, meet a hero we'll Regomize as "Mick" who worked for "a large Aussie telco" in the 1990s (a time when there were not …
Yes, that was the first time I heard a high amp switch do its thing.
It's a good thing I noticed the electrician cranking it up so I was expecting some drama but it was still surprisingly loud. That said, if you have copper bus bars that thick leading into the electronics you know the on/off switch will not be subtle..
A friend of mine reached behind a large bank of relay racks and managed to get his Rolex watchband across the 48V supply ... The resulting loud "CRACK!" and fans spinning down, coupled with the smell of roasting/burning pork, were rather disturbing. To say nothing of the screaming. I managed to calm him down & get him to the ER ... Xrays showed little balls of gold melted into his wrist behind the 3rd degree charring. The surgeons later told him he was lucky to still have full use of his hand. Today, 25 years later, the scarring is still impressive, despite skin grafts. He got a new band for the watch, and now wears it on his other wrist. It still works.
And people wonder why I always take off my wedding ring when working on electrical stuff. Yes, that includes cars, trucks, bikes, boats, etc.
when i was in the USAF taking electrical training as a prerequisite for my MOS, one of the safety films they showed us had a section with a hotdog wearing a wedding band... it showed what would happen when different electrical charges were applied... yeah... certainly eye opening and led immediately to quite a few of us transferring our rings from our fingers to our dog tag chains... without question...
If you've had any contact with old fashioned mainframes then you'd know that voltage isn't the issue, its current -- you remove all metal from your body to prevent this sort of accident.
The other thing that you don't really think of is that if you do get a high current short the resulting magnetic pulse is strong enough to move loose tools.
Telephony generally runs on a nominal 48 volts DC, supplied by banks of very open-vented lead-acid batteries; which have the advantage of not needing much in the way of over-charging protection, as long as someone can go round every so often and top them up with de-mineralised water. (Also, lead is pretty much indefinitely recyclable, and there's no way for it to get into your system down the phone lines.) This is the kind of power source that just melts its way through short circuits without even flinching.
If you stick an AVO across a UK phone line*, you'll get about 50 volts (with plenty of resistance in series; that would originally have been the coil of the doll's-eye in a manual exchange, later the line relay). Maybe a bit less in rural areas a long way from the exchange. There's no reason to suppose the Australian GPO would have done things any differently than at home.
* Don't hold the probes on with your bare hands as a call is coming in .....
This kind of thing played merry hell with modem connections - especially when their internal charge depleted and they started pulling more line current (changing the line impedance)
in the 1990s, about 2/3 of the fault calls my ISPs got about not being able to maintain a connection was traced to a cheap line-powered phone with last-number-redial or (worse) 10 memories
Before 48V at the exchange, there would be 2 _VERY LARGE_(*) dry cells screwed to the wall adjacent to the (crank handle) telephone
I spent several years of the late 1970s living in one of the last such areas in New Zealand - and a decade later was part of the project replacing all that (and the party lines they were on) with a full digital system, mostly served via multiaccess radio bearers
(*) EverReady No6 - 2.6 inches in diameter, 7 inches long and weighing nearly 2 pounds apiece. They lasted 20-25 years in service
The small community where my parents grew up has one of the last party line telephone systems in the United States. We decommissioned it "officially" in 1972. After disconnection, $TELCO left us the obsolete equipment to dispose of as we saw fit.
Unofficially, it still works between two dozenish homes, mostly family members. It is possible to call me there by dialing one of two numbers we maintain specifically for the purpose, and then having the operator (or a computer, on the second line) patch from $TELCO to our party line[0] and then ring the requested number.
In the other direction, four short rings automatically patches you to an outside line, normally used for emergencies only these days (thus the computer controlled line ... the human operator is an elderly cousin). Then you rattle the hook to tell the computer what number to dial. Yes, it's slow to dial out ... but it has saved lives on at least two occasions; cell phones don't work well or at all in this part of the Mendocino County back woods.
Mostly it's used for birthdays, anniversaries and other family stuff like that. My "number" (inherited from my Grandfather) is two shorts & two longs.
[0] Don't panic ... it's legal, I built a couple of optically isolated circuits specifically for the purpose.
Almost right - except that there's no regulation, the battery bus goes direct to all the equipment. In the days of relays and multiselctors, that would mean the raw 55V direct across the live via the off hook relay.
Having seen, and had operation thereof explained to me, a 200line private exchange I am immensely in awe of the guys that designed all those bits of mechanical stuff. Pick up a phone - the finder searches for a spare line. Dial the first digit, the first step multiselector clicks upwards with each pulse. You dial the second digit - the mechanical mechanism differentiates between the inter-pulse space within the digit and the longer delay before the next digit, then steps round. And so on.
Absolutely fascinating to watch. I would imagine seeing a full size (i.e. town size) exchange would be quite a sight and sound to behold. I'm told experienced engineers could tell if there was a major problem just by the change in sound.
I raise a virtual (see icon) to Almon Strowger and all those who followed and refined the system.
48v DC is also what you will find in the batteries for home solar. DC is way more dangerous than AC at comparable voltage because DC doesn't transition to zero volts 50 or 60 times a second: an AC switch used in a DC circuit becomes an arc welder.
48V DC is considered "safe" as it's too low to cause a grip reflex. For DC you generally need more like 500mA to lock up muscles (as opposed to 10mA for AC) and you are going to need a fairly exciting voltage to push 0.5A through a person, at which point a bigger concern is going to be barbecuing them.
Obviously you can't get a defibrillation type shock from DC.
Switching DC, especially at very high voltages and currents, is 'interesting' and particle accelerators powered by a room full of capacitors can cause a certain pause for thought
"Wet hands and 12V can hurt pretty badly"
As I remember from my childhood, 12v through wet shorts hurts a bit too. Was paying scalextric with my best friend one hot summer day and I already had wet shorts from sitting in a puddle of spilt fizzy pop. Crawling under the table to retrieve my car that had spun off I somehow ended up sat on the track as my friend squeezed his trigger hard to set off on a fast lap.
I was sort-of bracing myself to some deadly spider or snake hidden in the bowels of the telephone exchange causing trouble, but no assistance from the local fauna was needed for this mishap.
It does remind me of the time I was installing a new, far more robust dimmer system in a cafe I used to frequent. Before attaching the new dimmer system to the mains supply, something prompted me to check the wiring. My suspicions were quickly confirmed when (amongst various other horrors, I found a green/yellow (earth) cable actually being used as the live 230V 16 A wire. Not something I would recommend. I corrected some of the worst transgressions before hooking up my dimmers. I also told the owner to get an electrician to sort out the other horrors I found. I am not sure if he did, but my dimmers worked flawlessly for several years, until the cafe was sold and completely renovated.
My old house had this. We had a sparky in to trace and fix some odd electrical glitches (lights in the living room dimmed when the oven was on etc) - he found that the house had been rewired over the years by (presumably) the previous owner who just used whichever electrical wire he happened to have handy; it was all sorts. Red, black, green/yellow, blue, brown, indiscriminately and indeterminately live.
There was also a very odd construction whereby the whole back of the house wasn't wired through the walls, but by a big old wiring loom run direct from the meter cupboard, laid along the attic floor and down again at the back of the house. He found this out when he was installing a new attic trapdoor for us, was using a reciprocating saw to cut the hole and managed to saw through said wiring loom which was lying on the plasterboard.
Red, black, green/yellow, blue, brown, indiscriminately and indeterminately live.
I was once helping a friend diagnose a problem with a light in her old French house. We eventually realised that the live red wire that exited from a wall was the same circuit as the green/yellow one on the other side of the wall. After digging out some plaster I found that the two had simply been twisted together and wrapped with sellotape, before being embedded in the plaster.
At least you got colours. At my place, once upon a time, a spur socket had been installed by whacking two rows of nails into the wood and using some sort of fine bare wire (like that used for old fashioned electric fences) running from here to there. Diagnosis? Bad smell and very mangled rodent. I tore that crap out and installed a run of normal 16A cable.
I had a look for anything else as bad as that but it's just French farmhouse bad - light switches have fuses but nothing else did, stuff tapped off a three phase loop at random, earthing is best described as "maybe", and for added fun there's a run of three phase where the wires are blue, blue, blue, blue and blue. Oh, and *five* different types of sockets (5A normal, 16A normal, 16A huge, 3 phase old (no N), 3 phase new (5 pin)).
Way back when, the surveyor said this wiring was "to the standards of the time it was installed" (I guess he missed the bare wires) and that it was one of the better farmhouse installations he's seen. WTaF!?
Sellotape? Luxury! :)
It's several decades ago, but when we moved into a different house I was horrified to discover that the 'shed' was wired up with figure eight loudspeaker cable, just twisted together. No further insulation from where it took a feed directly of the three phase 380V mains cable that passed through there into the house, hell no, straight off a 25A main fused phase and neutral.
Given that the shed would also be where my dad and I planned to have our workshop (it was 25m long, the previous owner decided to make it the length of the garden), it was pretty much the first thing I ripped out and replaced it with properly fused and RCD protected three phase circuitry and lights along the whole length. Nowadays you cannot sell a house with such bad wiring as you need it certified before it can be put on the market - IMHO totally sensible. Having simultaneously an electrocution and a fire hazard is in my opinion a tad too much on the wild side..
Our place was similar, if not quite so bad.
Two sheds at the far end of the garden, with wire coming out from somewhere underneath the eaves of the conservatory (wire being standard cabling, think what you'd find coming out of a table lamp) and then cleated onto the fence (without any protection) up to the first shed. It then went in there, out again and down into a sunken piece of plastic pipework under the paved area between the sheds and up into the second one.
Pipework wasn't at all sealed, and of course was full of water, leaf mush and general muddy crud. Alarm bells rang when I first saw it, heightened when I heard previous owner mention that breakers had been tripping over the winter for that part of the house...
Needless to say it was the first thing that got disconnected, and as the sheds were both fairly much rotten anyway they didn't last much longer.
Said previous owner was I believe a school headmaster, and over the years we've been in the place, we've uncovered all sorts of other delights that he's similarly bodged.
His enthusiasm for DIY far outstripped his ability, but that particular one had to be the worst offender (at least so far)
In Belgium it's now mandatory. You need a house energy rated and the electricity needs to be signed off by an electrician. The latter can be a right pain if you have old wiring, but given the horrors I've come across in places before they made it mandatory* I think it ought to be mandatory everywhere.
* Years ago I saw a place which had the neutral of a 3 phase 380V setup fused. Imagine electric radiator on one phase and a radio on the other, and then the neutral fuse pops <shudder>.
UK also require Energy Performance Certificates - which are often not worth the paper they are written on as they use "assumptions" (mine "assumed" insulation was in place as it was required when the house was built, but it took me a lot of time and effort to put it in after-the-fact).
There aren't that many domestic properties in the UK yet that have three phase, but that's going to change with the move to EVs, heat pumps and solar/battery systems.
Fuse in neutral is still found in the UK (though is not permitted) - often where a legacy DC supply was upgraded to AC a long, long time ago. These are treated as emergency repairs when they are found!
Making the supply of a mandatory condition report on sale is a good idea - though the UK system would likely require it to be commissioned by the purchaser, which is the (crazy) situation with building surveys in England, as it means the same report can be sold to each interested party.
When we sold our French house we had to get an energy performance certificate. The technician turned up with his laptop loaded with the software, and carefully entered all the details: house construction, window sizes, thickness of double-glazing and loft insulation, etc. he then hit the 'calculate' button, and generated the report.
He asked me how the estimated gas consumption matched the real one, so I showed him a bill. He was so astonished that he called the estate agent over to show her, they'd never seen the program estimate get within 1% of reality before!
> had the neutral of a 3 phase 380V setup fused.
You can do that with US "split phase", 230V center-tapped. This building was too new to have fused-neutral follies, but low-bid builders can fail to tighten the white ("Neutral") wire.
I plugged-in a 100 Watt sound system. Sounded really good! Then FWOOMPH! mushroom cloud to the ceiling. Main filter capacitor burst, boraxed paper shreds all over the inside of the case.
The gal in the office said her coffee-maker was hardly warm. Hand-meter showed 50V on her outlet but 180V at the outlet I had used. Autopsy with the building electrician found a loose screw in the breaker box. The 1500 Watt coffeemaker hogged the 230V split leaving most of the 230V on my system.
Main cap was the size of a soup can, real mess in there. But new cap and all was well.
Yup. that's exactly the risk of a broken neutral - wether 3 phase or split phase. Many a house fire/mass conflagration of electrical equipment has been caused by scrotes stealing the neutral earth link from a substation.
Of course, the other one to watch out for is with our (in the UK) common TN-C-S system, the earth connection provided by the DNO (distribution network operator) is simply tapped off the neutral wire which is supposed to be earthed at multiple points (the substation, and typically at joints in the cabling. If the CNE (combined neutral & earth) conductor gets broken, then not only do you have unbalanced phase voltages (so some get their equipment blown up by high voltages), but everything "earthed" can become live. Inside the house that's managed by equipotential bonding, but plug in (say) your EV and you can have the car body live right next to (say) a lamp post that's nicely earthed by being planted in the ground. That's why there are special regulations for EV charging points which have to have "lost neutral" detection or protection.
The house I am in now was previously owned by a guy who owned a local factory of some kind.
According to my neighbours, he had a handyman (one of his <cough> "engineers" from his factory, apparently).
Said handyman did an awful lot of electrical work.
And earthed absolutely none of it.
A quick list from memory (and there was much more): a 32A commando socket in the garage: earth bent out of the way at 180 degrees and no sheath; extractor fan in the kitchen (all stainless steel - nothing on the earth tabs from the motor feed), outbuildings (no earth at the fuseboard in the first building), three out of 5 sockets in the kitchen...no earth attached, no sheath.
Quick (wago) connectors used to join cables but then not put into the outer boxes, and left laying on a shelf in the outbuilding above head height.
Electric gate controller - nice, wire armoured cable down to it from the garage. Ah... someone did something properly? Nope... No earth tab in the compression gland. No earth.
Oh and one of the en-suites has an electric shower. The isolator for that... in the built in wardrobe adjacent to, but outside the bathroom - a 32A cooker type switch (fine in terms of load for the shower in use, but less so in terms of easy access).
Once I'd fixed all the earth issues etc, I replaced the old wired fuse board with a modern consumer unit and RCBO's.
I genuinely think people fail to understand how dangerous mains electricity is because you cannot see or hear it unlike gas and water.
switch off mains sockets to stop the electrify leaking out.
When I was a kid I remember old ladies inserting plastic three pin plugs into the wall sockets to prevent the electrickery from leaking (even with the switch off.)
I never saw these plugs in the usual shops so I imagined there were specialist boutiques for this clientele: Dotty Old Dears 'R' Us.
I just realized that these plugs were probably sold to parents of enfants to prevent, or deter their offspring from inserting needles, hair pins and other conductors into the active of a mains socket.
Teenagers presumably don't hang about in nursery shops - gymslip brides perhaps excepted.
I never saw these plugs in the usual shops so I imagined there were specialist boutiques for this clientele: Dotty Old Dears 'R' Us.
If you mean what I think you do, they're actually from the other end of the age range.
Places like Mothercare, Ikea and similar stores sell them and they're to stop wandering toddlers and crawlers from sticking their fingers (or anything else) into sockets.
Edited to add - as I see you've realised yourself as well...
Places like that _used_ to sell them. They are strongly discouraged in the UK by safety bodies, because UK sockets are safer without them. They're bendy enough to make it much easier to retract the shutters on L and N than any other way short of poking a screwdriver (or similar) into the earth.
Some of them push the inner protective cover out of the way to expose the contacts and leave a small hole in the corner just big enough to poke a paperclip in to...
> poking a screwdriver (or similar) into the earth.
A key will usually do it. Just the once in some of the houses mentioned above.
Not to mention, not one of them meets the dimensional standard for something to be inserted into a BS1363 socket (a.k.a. "13A" socket) and hence liable to cause damage* which increases the risk further.
The damage can be impossible to spot, so really the only possible advice if you see one in use is to advise that it be removed and destroyed (to prevent re-use) AND the socket replaced. Many are so badly sized that they hold the shutter open, while making it easy to poke something into the live hole. See Fatally Flawed website for more details. In particular, see the Size Matters page there.
Electrical Safety First have designed a plug checker that you can keep in your wallet. It's worth getting several as once anyone who gives a toss is likely to ask if you can spare it when they see you use it (memo to self, need to get some more !)
*Some will damage the shutter mechanism, some will over-stretch the contacts and cause lower contact pressure and hence overheating when later used for a high power appliance, and so on.
Those things were at best redundant (BS1363 specifies automatic safety shutters on the live and neutral socket holes) and at worst actively dangerous (capable of misuse in a way that creates a situation where said safety shutters are left open and accessible for things to be inserted into). See https://www.fatallyflawed.org.uk/ .
We even managed without half-sleeved pins for a very long time; because if you used the socket faceplate switch properly, the exposed parts of the pins were never live. (Though there are a lot more extension leads around now, with unswitched sockets, than there were in 1947 when the standard was drawn up; so this probably isn't too bad an idea.)
James Thurber wrote this about his mother - "The telephone she was comparatively at peace with, except, of course, during storms, when for some reason or other she always took the receiver off the hook and let it hang. She came naturally by her confused and groundless fears, for her own mother lived the latter years of her life in the horrible suspicion that electricity was dripping invisibly all over the house. It leaked, she contended, out of empty sockets if the wall switch had been left on. She would go around screwing in bulbs, and if they lighted up she would hastily and fearfully turn off the wall switch and go back to her 'Pearson's' or 'Everybody's', happy in the satisfaction that she had stopped not only a costly but a dangerous leakage. Nothing could ever clear this up for her."
I cut what the mother feared from the record player, whose source of power was mysterious to her, but which I take to be clock-work.
"I genuinely think people fail to understand how dangerous mains electricity is because you cannot see or hear it unlike gas and water."
I think part of it is that lots of people - especially the kind of bodgers we're talking about here - have at some point experienced a small mains-voltage shock, and think that's as bad as it can get.
I have experienced "a small mains-voltage shock" as a child, and I do not ever wish to experience that again (genuinely unsure how exactly I survived, but properly wired and rated circuit breaker almost certainly helped).
Mains electricity is "fun" if you know what you are doing, that's why, when I had my house re-wired I payed a professional to do it properly.
Thing is the circumstances of the shock - not to mention the individual's skin resistance - can make a huge difference. I was fortunate enough that the last 240v mains shock I had (while twisting together wires that were supposed to be isolated), left me musing to myself "hmmm, that feels a bit spicy, what's going on here.... oh *shit*, better turn that off!" rather than throwing me across the room. I'm not blasé about it, though - I'm well aware that had my other hand been touching something earthed I might well not be telling the tale.
BTGTT-S for throwing across room type shock... even ended up in a 'Dyson Wheelbarrow' for comedy effect. I was disconnecting a bypass relay and grabbed the switched tails rather than the coil tails (both of whch would have been stupid; one slightly less stupid than the other).
I was very lucky indeed - on site, lone working, caretaker away for 14 days, car parked out of sight, no-one actually knew I was there.
I was, subsequently (and still am, even though the day to day job has changed so things that go zap quite like that are a dim and distant memory) very careful around things that might go zap after all these years (35ish)
I would like to say it taught me not to override interlocks...
That doesn't sound like what I'd call 'small'! I've had a shock from mains wiring that was about like banging your funny bone, which seems more the kind of thing to lead idiots to think mains voltage can't really hurt you.
Then again, there are lots of idiots out there. I've seen someone trip a breaker - but fortunately not get hurt - working on a bathroom extractor fan, which, of course, has both switched and unswitched live, after turning off the light switch 'so there's no power to it'. I've also seen an electrician strip live wires with his teeth; he claimed that a good electrician can taste the difference between phases :)
This happened to my father while we were on holiday in Italy. Old Chevrolet with 235cu in Blue Flame engine, one of the hydraulic valve lifters decided to give up the ghost and started clattering. Dad took off the rocker cover to adjust the valve clearance, and whilst so doing managed to short from battery live to the earthed battery clamp with the elastic metal watch strap.
Howling in pain, he pulled the strap away from his wrist, thus burning the tips of the fingers of his right hand. Letting go resulted in the strap springing back and burning a different part of his forearm. Rinse and repeat, and he had three parallel burns on his left arm and three burnt fingertips on his right. I had to take over the driving duties for the rest of the holiday as he was in too much pain and too drugged up with painkillers to drive safely.
Worst holiday ever.
I used to take my wedding ring off when working in the HV lab in my R&D department, but forgot to put it back on before I went home one night. It was the final nail in the coffin for my (now ex) wife who accused me of 'obviously' carrying on with someone at work. That fact that I'd actually managed to get a 880V shock while developing a 3 phase syncroscope did nothing to convince her of the dangers I faced every day, in an attempt to fund her lifestyle.
Oh well, it was a blessing in disguise, but I've never worn a wedding ring since!
In my high school physics class the teacher was very much of the "I wonder what happens if..." school, and when we were doing a unit on electricity he wondered what would happen if you shorted out the terminals of a 12v car battery. Or maybe he knew but wanted to give us a fun demo (he also liked making sparks/fire in class) He dropped an old screwdriver across the lugs, and there were a lot of sparks and it welded itself across them! Once it cooled down he asked for volunteers to try to remove the screwdriver, none of us could - even standing on the battery and pulling on the screwdriver with both hands! It wasn't a pretty weld but it was a stout weld.
I've told a few people that story over the years and some are skeptical. After all it is "only 12 volts". I always tell them "try it yourself" (but make sure the wife isn't home)
Any modern battery will likely have a "CCA" figure on its label. CCA stands for Cold Cranking Amps, & is the nominal maximum current that the battery can deliver to the starter motor for a specified duration at the specified ambient "cold" temperature. I can't remember either of the specified values, but you get the general idea.
As an example I need a replacement battery for my 1992 Saab turbo convertible, which never leaves it's dry garage on anything other than perfect days, so is perfectly happy with a low output battery. The existing (now dead) one is rated at a CCA of 550A. I've been "off the spanners" for almost half a lifetime now, so am out of touch with the techie aspects of modern motoring. (Daily drive is a 1997 Volvo V90 which I've had for 22 years & which shows no sign of wearing out. As long as that persists I intend to remain ignorant of CanBus, & all the other "enhancements" of modern motoring.) Consequently I only know that, with all the electrical loads on a modern car battery, esp the capacity to power the mandatory Stop/Start systems, CCA requirements will surely be significantly higher, often solved by many cars now having two full sized batteries I'm told.
From a previous life as a Saab tech, I have in my toolbox a 10mm combination spanner with a right-angle bend in it as a reminder never to rush a battery installation. In a moment of inattention I allowed it to touch both battery terminals of a brand new battery (on a 900 so at least 550A CCA) momentarily, & it immediately tack-welded itself in place. In the couple of seconds it took to grab an adjacent screwdriver & lever one end of the spanner off the lead post (thank chosen deity that lead is soft) the spanner was already glowing cherry red & it just bent round as if it were made of hot toffee.
I have no idea how many amps a shorted car battery can deliver.
"A good few" thousand amps if it's a hard short.
With a different work hat on I had the experience of working with batteries which were "quite a bit larger". I later came across an old document from when they were type tested. The short circuit test was probably "quite interesting" - short circuit current in the order of "a few tens of thousands of amps", and a battery of "a few hundred" volts, you do the maths (see icon). Needless to say, there are some very stringent safety rules around the batteries and associated cabling and protection.
"The other trick was that the installation had to be done while the power was live. It was, after all, a telephone exchange, so shutting it down for any length of time would represent a great pain in the proverbial."
Now that's not what I call a safe environment.
"It also blew the main 100 amp fuse – cutting power to the entire exchange."
How many amps were running into that station ? Blowing a 100amp fuse is not a trivial affair.
I can't understand either if the 50V was the correct value but at any rate the unintentional electrical spark fest must have been nerve racking to say the least.. It probably made a nice bang too..
And I still can't understand the need for the second 16 amp fuse ?
My favourite fuse fact: given a sufficiently high current, some fuse types will vaporise and continue to allow current to flow through the metal vapour.
Given a sufficiently high current, some types of fools will vaporise and continue to allow current to flow through their carbon vapour.
I imagine a fairly gruesome carbon arc lamp.
> ...used to be a sausage cooker that connected live to one end of the sausage .... .... Dangerous? No, of course not.
"Presto HotDogger" in the US. Power feeds through the removable clear cover, what could go wrong??
https://www.youtube.com/watch?v=JBEEgkuowH4 --bigclive with sausage pastry
https://www.youtube.com/watch?v=MSd2-lFjV94 --oversized but proper hot dogs
My parents would never buy me one. So I used stripped linecord and nails.
Forgot to mention that the same contraption will turn a pickle into an electric light (for small values of light).
And I should also mention that you probably shouldn't try this at home, 'dog or pickle. It's pointless, and dangerous. Plenty of videos out on TehIntraWebTubes to show you what happens, and there is no point in wasting food. Or forks.
Quite a few years ago I encountered three YouTube clips, apparently posted by students from their student house, of them "cooking" a sausage by poking a fork into each end, wrapping the bare ends of some stripped mains cable around each fork & switching on at the mains. After a brief interval a sizzling noise became apparent & the sausage proceeded to cook from the inside outward. IIRC it was OK but a bit under done.
The other videos had them cooking pasta in a kettle & frying bacon on an upturned iron (as in clothes) supported on two bricks. That last was a bit of a fail I vaguely remember, possibly due to the iron being insufficiently level, & the coefficient of friction between the oiled iron & the bacon being too low to prevent the bacon escaping.
Hello to any student landlords in da house...
Those were the original Tom Scott videos IIRC
eggs and bacon on an iron - https://www.youtube.com/watch?v=MrppkAIVhH4
pancakes on a light - https://www.youtube.com/watch?v=nkTyWTC9UZc
pasta in a kettle - https://www.youtube.com/watch?v=sZ363XfT8fk
salmon in a dishwasher - https://www.youtube.com/watch?v=6N8q2xkirCQ
can't find one with sausages and nails tho
some fuse types will vaporise and continue to allow current to flow through the metal vapour.
All types of fuse, and any rating, will do that - but if properly chosen the arc length is too long for the supply voltage to sustain it and the arc goes out. The higher the voltage, the longer the fuse - if it's too short, the wire will burn back (leaving said cloud of conductive plasma behind) until it runs out of wire and spits out of the end of the tube while arcing between the terminals/end caps.
And in circuit breakers, even the small domestic ones, they generally have an arc chute design that causes the arc to expand sideways and impact on a set of vanes which break it up - or some large ones use something like a blast of air to blow it out. Yup, high energy arcs are ... interesting. Worth looking up on ${favourite_video_site}.
100A at 50V is only 5KW and it will have been pulling less than that under normal circumstances.
Yes, 50V is standard in these environments. Technically -48V to -53V (the positive terminal is grounded as this polarity reduces corrosion) That's made up of 48V nominal on batteries (easy as 4x generic 12V batteries, but usually ended up as 24x big 2V cells) and the charger running a bit more than that to maintain the charge. This is also the standard that influenced PoE voltage.
The 2 x 16A fuses will have been 2 drops into the rack. Probably for a bit of resilience in case some of the kit shorts out. Possibly because the rack needed more than 750W and 16A fuses were standard on drops.
> This is also the standard that influenced PoE voltage.
Long before that: "phantom power" for condenser microphones. These needed power in the mike. Mostly broadcasters could afford condensers (Neumann was the big name). Broadcasters had telephone relays and switchers everywhere, 48VDC was standard juice.
It is notable that battery portable tube "beach radios" used as much as 90V, this was almost always as two 45V batteries (series), not a single pack with 90V begging to be touched.
Wires where your baby can chew on them, 24V is a common limit. (Cats can be mouth-maimed or worse with less.) Wires not normally fingerable (covers, closed connectors) by The Public: 48V nom is often done. That's steady-- the 90VAC of ringer-power is intermittent (you have moments to let-go) and anyway was necessary at first and then quietly accepted because only the few guys in this thread felt it, and few of us died of 90V ringer.
Lots of mamps, Telecom Exchanges usually geets their 50V mains in the form of copper bars 5cm wide by 10cm high...
In the 90s, a single shelf in a rack could use between 50 and 200 amps...
My guess it was not a full exchange sitting the outback, but some remote subscriber stage and a few retransmission equipments for long distance transi.
So by blowing the 100 Amp fuse he killed the control links from the actual exchange to the remote subscriber stages in the area ( the long distance equipments ) along with the local remote subscriber stage.
Once upon a time had to set up the fuses on several remote subscriber stages for initial startup... and actually I was more worried by the massive capacitors at the botom of the whole enery providing rack than the even more massive fuse and it's large red fuse insertion tool. ( because I didn't have the charging resistors at hand and counld't precharge the capacitor, I had to do it through the fuse without blowing either by the seat of the pant, and the while making sure that nothing was going to touch the two massive copper bars on the side of the rack in case of any issue )
I saw a big spanner mounted on a nice wooden plaque in an exchange - the spanner was melted through the middle into two pieces.
The story was that a tech walked along on top of a cable way and banged his head on a concrete beam, causing him to drop the spanner onto the main power bus bars. The whole exchange went down and back up.
Such an event made much money, since everyone had to call again and got dinged for a new call.
I did that years ago when I was a student, but was saved because the battery was already pretty knackered and was only being charged by a dynamo. Ah, the glory days of British Leyland.
I swift blow with a hammer removed said spanner (and half of the terminal) but it still managed to get me though the next two terms until I could afford a replacement.
I have seen this happen once, it’s very spectacular.
I believe that one of two things happens, either the spanner manages to weld itself to the battery terminals, followed, promptly, by explosive vaporisation of part of it.
Or it somehow jumps 2m in the air and when recovered has changed shape and/or has a hole or two in it.
Rapid high current discharges are weird things.
In the first place I worked, we had a goods lift that could lift three cars at a ttime onto the roof, so it used a lot of juice.
One day we lost power to the lift, so the maintenance guy came out, checked things over and decided we needed a new fuse, he pulled one from his bag, it was the size of a beer can, rated to 400 amps.
Wearing very thick gloves and weilding a sturdy pair or tongues, he removed the old fuse. The belt of lightning as he put the new fuse in place was a sight to behold. It also took out all our power and the neighbouring units either side.
Maybe he should have checked the power was off first...
We were moving a show into our town hall - with full lights. We had put a request in weeks before for a socket for the 3 phase power we needed. We were told it was done, so we were happy.
We arrived at the town hall Sunday 0800 to find the work had not been done. We complained and were told the electrician would be in first thing Monday morning - no good for us as we were performing Sunday night.
Our lighting guy said he would fix it. He worked installing radar sets as his day job, and was used to "rewiring live". We could not turn the power off to the building, so he had to do it live. He said he had come prepared - rubber soled shoes, a broom, and his screwdrivers. The broom was to push him away from the power if there was a problem. He said "clear the stage" in case anything went bang (eg flying screwdrivers).
He wired in our lights successfully. He said the problem with doing it, was you sweat .... which is a good conductor, so you do not want to drip.
This was about 40 years ago... so none of the modern risk acceptances.
When I was in EE school, there was a laughably inadequate yet mandatory safely lecture before we were allowed into the lab for the first time. The two things I remember from the 20 minute presentation:
Some of the comments remind me of a time when I was conducting some site audits of one of the UK's electricity companies (not my usual fare but what I needed to verify was well within my professional remit). On one particular visit, I was looking at transformer oil changes in a local sub-station - one of those large-shed sized buildings you see around the place - this one was on a well-known sea front. Before entering the building I was told not to touch anything inside as the steelwork I'd need to stand beside would be carrying the 3-phase 440V supply. Sure enough, it was definitely a "nicht gefingerpoken" area. The oil had been changed and I was just needing to verify tags, so no need to touch but, once I'd done that my host had to reconnect power: for which he put on some heavy duty rubber gloves, picked up a hefty steel bar and used it to lever on the breaker in aforementioned steelwork. Slight arcing across the contacts, but that's what they're made for.
AC poster here - definitely steel as I still remember the clang as he threw it back into the toolbox. I should have added that he also stood on a rubber mat whilst closing the breakers.
AC because I had to write up a safety issue - even though the substation was securely locked (to keep kids out) it would have been quite easy to have put guarding in place to reduce the probability of a worker accidentally touching (nobody is immune from slips and trips).
Again old skool telephony, live system, 50V battery.
This time in the UK in the late 70s and I was installing some new shiny digital optical kit for a big utility in a room full of gently humming racks and blinking lights After the mechnical installation was done, the next step was to connect the new kit to the 50VDC bus bar which was of course live. This involved feeding the big fat red wire through trunking and racks, tying it up neatly with waxed string into the power loom and then wrapping it round a tag on the bus. It then needed soldering to the bus!! We had an almighty 'unearthed' soldering iron for just this job, so when it was really hot and almost glowing I touched the iron to the tag and kzzzrrttt *BANG*, silence and at least one 'oh f**k' from the asembled station staff. The cable to the iron was a smoldering smoking dripping mess. Lucky I was wearing large glasses fashionable at the time as I was showered with bits of molten copper, thankfully no serious burns. Turns out a helpful apprentice had noticed the iron was not earthed and 'fixed' it on a previous job. Took out the west midlands network for several hours while everything was fixed up..
Soon after they changed the procedure so a nut and bolt was used to connect new feeds to the bus bars with a crimped eyelet.
I'm sure that all of the 47 people who were living within that 1600 km radius will now be mighty relieved that the cause of the great mystery has been revealed at last!
(Stating the obvious, but there's an almost unbelievable amount of empty space in parts of the Australian outback…)
I might have told this one before. But years ago I was doing some work which required moving a lot of digital phone cables out the way so we could install some new fibres. Now for safety we were running the fibres under the telephone cables as they were due to be ripped out a few months later.
So one Saturday night myself and.a colleague where sat side by side (shoulders almost touching) whilst lifting the floor tiles and the cabling to run in the new stuff.
Sitting on top of the telephone cables was a brand new 32A commando socket needed for the new kit.
So I pick up the new commando to move it out the way, there was a bang and the building went dark. The Electrican hasn’t tightened the screw holding the earth cable this fell out of the terminal and dead shorted the building power as it went through and tripped the main breaker for the building.
Now the Monday after this I had a day off, at this point the rumour mill went into overdrive as I had
Had an electric shock
Been hospitalised
Died
Despite my colleague saying I was ok and if it had been that dangerous he would have been in the same state.
Ps the electrical contractor company was fired and banned from the site.
Many years ago I was asked by a stranger to help jump start their car. all went welluntil they removed the leads from my battery and in order to shake my hand put both leads together into his left hand..... To say he jumped is putting it mildly - he also lit up the surrounding area!
A friend used to work as a night shift (single person) dispatcher/something/something for a large (well, the main) local power company in Eastern Europe in the early 90's, as a side hustle.
One night there was a fire alarm somewhere down the (power) line and as part of his duties he had to disconnect some main circuit for the firefighters to be able to proceed.
Disconnecting the gizmo was purely mechanical and required pulling a long lever, located in a niche with surrounding black baffles, pointing away from the circuit. The lever would then pull a quite complex pantograph which would disconnect the main circuit. I don't remember the details but the volts were deeply into quadruple (or was it more) digits and all the cabling and connectors involved were on the beefy side.
The procedure was quite specific. My friend of course being the Jedi that he is managed to simplify it and skip all the useless steps, like - actually getting the baffles up, disconnect something prior to avoid arcs - forgot the details.
Or maybe was it that he had to skip a step because of something else not working, and he knew an arc was likely to happen - which was unwanted, but not critically bad.
The short story - he did disconnect that thing, looking at it , with a brave safety squint (he actually looked at the thing till the very last moment, then closed his eyelids the tightest he could at the very end before the arc buzzed).
There was a (Bright. Very Bright. Extremely Bright) arc and the accompanying buzzz to match. And his eyelids didn't help much.
He went back to his desk, his vision dim and lacking contrast like after a photo flash straight in the face, but not too bad. Logged his things, did his stuff. Then within an hour his eyes started hurting to the point of screaming. Then he lost his sight and went blind as a bat.
Medics came in, checked him out, said "Yeah, it's temporary, it's going to hurt like a MF then you'll be fine within a few days", poured some nasty drops in his eyes and called it a night.
Apparently - it hurt like a MF, and then he fully recovered within a few days. His thoughts in that specific time span between the "you'll be fine" and him getting able to see again was an interesting one, he says.
If memory serves - yes, it needed two hands. It was a manual lever with cables and counterweights and whatnot, moving the pantograph.
The niche the lever was located in was on purpose protected with baffles, facing away from the business end of the connector, and all that. But for whatever reason he had to actually stretch and peak out of the niche - was it to see if the correct pantograph will start moving, or for something else - I can't remember.
All this to say that "Engage safety squints" didn't work even back then in them good ole times when everything worked :)
Once when operating and installing "Roots Type Air Compressors" a safety outlet bypass pipe was blocked by Seagull Guano as they (the gulls) had 'nested' in the warm outlet pipe, and the nests built up to cause a big restriction to air flow.
When called to fix motors switching off, all fuses blown, shortly after every start-up. I removed all pipe connections to blower and its motor and ran it for many hours continuously without any fault or failure thus proving not a problem with motor or compressor. Re-attached normal air flow pipes, started up, and blew fuse on main district sub station (about 6 inch long 1 inch diameter fuse), cutting supply to many households. We then inspected pipe line, and found no faults but organisation would not let us on roof where bypass outlet was situated. We 'demanded' to inspect the pipe outlet on roof. "No, not a problem, it is open to atmosphere' was the answer. After much hassle we got on roof (many 'indemnities signed etc.) Inspected pipe outlet and found about three quarters of bypass outlet pipe blocked by seagull guano. They had found a very warm place to build their nests. Seagull guano when hard is very difficult to break up. We replaced the pipe and put a wire frame over the end.
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