How do you save an ailing sales pitch? Just burn down the client's office with their own whiteboard The Register readership knows no bounds when it comes to electrical snafus, as demonstrated by a Who, Me? entry featuring motorised mayhem and a certain South Korean semiconductor manufacturer. Our reader, Regomised as "Dave", was working for a semiconductor supplier as a Software Product Manager. "This involved," he said, "a …
I remember a near miss in a meeting, when we had been brainstorming on a whiteboard, and to clarify part of the design someone pulled the overhead projector screen down to project a diagram. After a few minutes of increasingly-excited discussion one of the engineers leaped to his feet and grabbed a pen, only to have half the meeting scream "STOP!!!" a second before he started annotating the diagram - on the projector screen. He looked quite stunned for a moment.
Only peripherally an IT issue but in one job the kettle lead had gone missing as we only discovered later. That particular kettle didn't have the bit that stopped you using standard cable instead of a hot condition one so someone had found a spare computer lead and used that. Inevitably a few weeks later the lead caught fire, fortunately whilst I was in the kitchen (didn't even need a fire extinguisher, I just turned the socket off). No damage done but could have been a lot worse.
I haven't used a kettle lead in years. We've had the upright, jug-like things with the lead hard-wired to the base and the kettle plugs into a coaxial connector on the base. First an old, well-respected brand and then, after its cheap and nasty clip closing the lid failed so the steam detector couln't work (if you've had the same brand you'll recognise the problem) and than an Amazon Basics, cheaper than the well-known brand, not quite so well balanced to handle but just works.
I was about to say I've never seen a kettle cable that looked like a PC power connection. Then I got up and looked at the kids old kettle and sure enough, it looks like a PC cable would plug in. But 99.9% sure it would not work well/long. The right cord is much beefier as a 1800W kettle should have.
You'd think wouldn't you?
In reality I've bought kettles rated at north of 1800W supplied with 0.75mm2 flex with a 13A fuse in the plug, type approved no less from a major retailer - the argument being "it doesn't run long enough for the flex to exceed its temperature rating" - (yet the regs say size flex according to the load, NOT "if it runs for a short enough time its ok to use heavily undersized flex that will get hot at the terminations to save a few pence per appliance")
Some friends of ours rented a cottage a few years ago back when such things were possible. It was for a long weekend in the depths of winter and my mate had picked one with an AGA Cooker for extra warmth. We arrived on the Friday and settled in discovering an unadvertised whirlpool bath in one bathroom as a bonus. After a countryside walk he'd made the four of us a pot of tea and toast. There wasn't a conventional toaster instead they had an AGA toaster which resembles a badly made metal tennis racquet. You stick that on the cooler hotplate and turn it over as required. There was a regular kettle and an AGA one that you put directly on the hotter hotplate. Both of these were in the same cream colour as the cooker. Come the Saturday morning and his wife volunteers to make the tea for them. The way he tells it he was in bed still enjoying the thick warm duvet in a post coital bliss when the smell reached him. He arrived in the kitchen to see the plastic base of the regular kettle happily and rapidly melting onto the hotplate.
It didn't stick too badly to the cooker, and when I got to the kitchen he'd removed it and was scraping off the remaining plastic. She blamed the cottage owner for having both kettles the same colour. Their first activity of the day was a trip to the local town to find a replacement. They subsequently bought an AGA for their house but their electric kettle is kept safely in a cupboard out of the way of temptation.
In the days when PC ATs were new, I balanced a brand new $LARGE-GB $EXPENSIVE drive on the edge of the case. It was a full-height drive.
Ah, I was expecting more of a "crash". I was testing some new large capacity at the time FH 5.25" ESDI drives all laying on a desk. May have been CDC Wren or something like that. The voice coil seek operations were violent enough to make the drive travel across the, admittedly fairly slippy, desk. Now if it had been balanced on edge of the case...
"Once witnessed a junior tech tasked with recovering data off a harddrive blow it up. I'd never realised that a floppy power cable could plug in to the jumper (master/slave) pins. The client was told the harddrive had died with the PC :)"
Ah, I remember the drives where the jumpers didn't have plastic surrounding them.... :)
Had a tech on his first day manage to plug the molex connector to a hard drive in backwards and let out the magic smoke. I heard him fussing and asked how it was going and he says "It doesn't work and it stinks!" Ended up finding a same-model drive and replacing the circuit board so we could get the customer's data off of it. 5 years later and the same person has been promoted twice and has a reputation for being lousy at IT, but an incredible brown-noser and back-stabber. I guess all of us are differently abled..
Many years ago was interviewing for an IT Support job. Part of the interview was "here's a PC, we've broken various things in it, make it work". Was things like one of the cards was loose. But I always first checked the voltage switch. It's just common sense. And after I got the job, I joked with my manager that I'd love to set it up for an interviewee with the voltage set to 110 and see if they spot it. Although I sometimes set that part of the interview, I never did that.
3 years later, I've moved on and I get an E-Mail from my former boss saying "Ha Ha Ha" and nothing else. He wouldn't reply to me. So I contacted one of my former colleagues. Seems whoever set the machine for my replacement's interview HAD changed the voltage switch - my boss assumed it was me! Unfortunately they didn't check and blew up the power supply when they tried it...
Oh well!
I had a graduate (a graduate in Electrical Engineering) working for me on some power-measurement tasks. He wired the three-phase instrument voltage-transformer incorrectly, leaving the protection-fuses the 'wrong' side. I never knew a solid, cast-resin transformer could spread so far. If you know where to look, the traces are still there, 8 years on.
I should have checked. I should have checked. I should have checked.
I took the blame, because I should have checked.
A rather large 3 phase machine in our workshop was going through its preventative maintenance routine, service engineer turned up, looked at the paperwork and realised it was all ok and all that was on his checklist was to check and replace the main fuses. Service engineer throws the isolator and tells his apprentice to get on with it as its a nice simple job.
Few minutes later apprentice comes back, "All done!". We suddenly realise the apprentice has come back from the "wrong side" of the isolator. Panic all round and service engineer goes white as a sheet as we try to work out what has gone on.
Eventually penny drops, as we realise that the isolation switch had been installed the "wrong side" of the fuses and the apprentice had somehow managed to change all the fuses on a live installation without making contact with any of the live bits. Either one very methodical or incredibly lucky apprentice.
Machine had been like that for years. Cue lots of red faced H&S types getting very angry...
Chatting to an engineer who was busy doing a warranty repair on a PC at the college where I work, the subject of switchable power supplies came up. He once had to visit a school and replace about 20 power supplies in PCs in the library, it turns out that one of the students had spotted the voltage switch on the PSU and flicked it to see what happened... Apparently he was quite enamoured with the sound, light and smoke effect, so proceeded to flick more voltage switches, until one of the staff caught him!!
Not told this one for a few years, so wibbly wobbly........
Customer ran his business off one PC & decided to see what would happen with that voltage switch, while it was in use....
Short version BANG!
Long version BANG!, PSU replaced, Windows wont' boot, d'uhstomer takes it home to reinstall Windows, brings it back next day & to save my fingers basically, the MBR was royally fucked & shenanigans ensued to clone the HDD, wipe the original then put a fresh build then copy the file structure back for the idiot to reinstall his accounting software & give him a very large (Second) bill.
Just over a third of a century ago my IBM Portable PC arrived -- a mere 30 lbs. of portability, though I think the keyboard added 7 lbs. more. It came with a postcard with a space for comments, and I mentioned that, though I was in New York, it had arrived with the power switch set to 230 volts. A few days later an IBM representative *telephoned* me to check on this grievous misconfiguration. Customer service and follow-up have changed a little since then...
On a similar vein, several years ago I was auditing a company that trained and certified electrical techs to work offshore. Part of the qualification process was a practical and they had a workshop with a wide range of kit they could encounter on site. One of the specific checks was on trainees checking isolation - all the kits LV but had a few flash-bangs hidden away and, if anyone didn't confirm the circuit they were working on was isolated, they'd experience an UUC* moment.
The significance of checking circuits was brought home one day when I got an urgent phone call saying one of our offshore contractors had divers trapped subsea in a bell without power. The divers had bail-out bottles to provide breathing gas for quite a while, and torches to provide some light, but their hot water suits would soon be getting cool. Power was restored fairly quickly but there was an investigation. We found they'd decided to connect emergency jumper cables from the dive-spread across to the rig supply - to save time should the dive supply fail (a separate generator). Unfortunately, the rig supply tripped during the dive (the potential of such being the reason the dive spread has its own supply); having pre-installed the emergency cables, the dive spread generator now found itself being asked to power the whole rig... and immediately shut off. Once the cause was identified, the cables were disconnected and the generator put back on-line (fortunately the breakers did their job).
*Urgent Underwear Change.
When I was on a Post in the ROC, back in the dark days of the late 60s, our SOP for when a Nuclear Explosion was heard was: " No 1 Observer, read Bomb Power Indicator, No 2 Observer Pass time and pressure to Operations Room over Teletalk, No 3 Observer exit post and change Ground Zero Indicator papers". To which some wag had added "No 4 Observer, change underpants".
My mother was in the ROC, I'll have to pass this on to her! I used to sneak a look at her paperwork as a boy, I seem to remember all this talk of sealing your house against fallout and such fair put the wind up me. It did make me question the worth of bothering to learn my times tables.
Sadly, and imo, stupidly the 11 to 12x table are mandatory in the UK. And part of the high stakes assessment, so that massive pressure is put on the kids to learn this stuff- with the concomitant reduction in the ability to learn it.
Not because it's much ( if at all) needed, but because the idiots who decide these things want to go back to the Good Old Days. Which means 12x table, rote learning and lots of useless testing.
I respectfully disagree. Having the times table all the way up to 12x12 ingrained in your head will stand you in good stead for life - as will the ability to break things down into smaller chunks and the ability to estimate the approximate scale of the answer before you mis-tap it in on the calculator.
Yes, you can argue that few don't have a phone to hand these days with a calculator on it, but being able to do basics in your head is often a lot faster.
You miss the point. I did not ever state not being taught the tables, nor using a calculator instead. You seem to be responding to some other view. I referred to the 12x table and high stakes rote learning. A very different set of issues.
12x12 has little or no 21stC utility and was made compulsory by politicians because that's how it used to be. Learning.12x12 owed its existence to the premetric measuring and money. What used to be called "reckoning". Knowing how many inches in 13 shillings. The 12x table is an arbitrary place to stop otherwise.
Tables to 10x10 are essential- at which point your breaking down into smaller chunks is the required skill (5x10 add 5x2 == 5x12).. We work in base 10, not base 12.
Also, learning the stuff is best achieved without high stakes testing. There is a world of difference between checking the kids know this stuff and using it as a target to measure school performance. That just means it becomes a must instead of a should. We generally recall better when not under a guillotine.
I'm sure there are still. But since it's hard to imagine anyone needing to do feet-inch multiples any more, hardly of relevance. I assume anyone using these measures- for whatever reason- will have learnt that specific skill, just as when I briefly worked in casino I knew the odds multiplication tables. Of no utility outside gaming.
From your comment, I can only assume you are "younger than I am" and also never have to deal with people of my age and older. There are still many people who work in feet and inches - and some of them (not me) will need you to translate if you want them to understand what you're talking about.
Often when there's something on TV, I'll start "translating" without thinking about it. Someone says "that mountain is 3000m high", I'll be muttering "that's 10,000 feet" for the benefit of SWMBO who has almost no concept of what a meter is.
Amusing tale - we got a picture frame for christmas off one of the family. It was too small by a factor of 2.5 - i.e. 40% scale. That means, SWMBO measured the picture (a university photo of mine) in inches, daughter ordered in cm !
... Ahh, the lovely stench of smoked capacitors in the morning. (aka plugging in 110 into 208)
That happened a couple times at [RedactedCo]- the first time was with a brand spanking new videio distribution system that was designed to use consumer-grade setup boxes for content acquisition. the installing vendor didn't notice until the third box went BANG instead of smoldered. At least they didn't set off the fire supression system as it was in the data center.
the second time was with a piece of very proprietary kit from a vendor that wasn't auto-ranging, which is on my standard list of questions I now ask ALL vendors before permitting any equipment to be installed in our data centers. :D
South Korea and the majority of the planet.
The thing that causes as much damage is also the AC frequency. The world generally runs on 50hz or 1 cycle every 0.02 seconds. Some weird places run on 60hz or 1 cycle every 0.01666666666R secomds. If you ever hear a good low buzz with some iffy piece of electrical equipment, that is a mains hum. Theirs is a worryingly higher note...
A few years ago the village where I live was having some major work done on the electricity infrastructure, so a massive generator was brought in to run everything. Power quality was really good, no brown outs or anything, but I did notice that clocks on things like the VCR (yes, this was a few years ago) the cooker, etc. were running fast. That was when I learned that (a) some digital clocks synch to mains power cycle, (b) some generators run faster than 50Hz
It's still a thing with microwave clocks and similar, and things recently went a bit iffy
Things even went iffy a couple of weeks ago. For values of iffy being "frequency went 0.3Hz off spec": https://www.entsoe.eu/news/2021/01/15/system-separation-in-the-continental-europe-synchronous-area-on-8-january-2021-update/
I'm so glad all I manage is a bunch of webpages for entitled academenteds and not power plants.
At Princeton U, there was a student lab to measure g using a pendulum. g was off more than it should have been. The prof investigated. Turned out the wall clock (used to measure pendulum period) ran off the local power company. The clock at the power company ran off same power. When 5PM approached, the workers' hand would move the generators a bit faster, so as to get home sooner. Hence wong g.
A) How much should g be off?
g=9.802 m/s^2 is an *average*, not a constant. Where I work, we have slightly lower than average gravity - 9.79747 m/s^2. Not a big deal generally, folks don't notice being 1-2 lb lighter, but it's definitely required knowledge when using calibrated weights to test force-measuring devices to ±0.1%...
Check out your local gravity! https://geodesy.noaa.gov/cgi-bin/grav_pdx.prl
I have exactly the same issue with a car radio. It has a clock on it and bluetooth. If I have it constantly connected, whenever someone walks by, it turns itself on as their phone connects. This leaves me with a flat battery, If I connect the radio through the ignition, the clock is never correct! cannot win.
And (at least in 1996) South Korea.
It took me 3 or 4 days to work out why a digitiser connected to a CCTV camera wasn't working (this was part of an animation line test system set up on an Amiga), it had all worked when several together in the UK installed the software and tested. I had even labelled all the connectors with matching sticky dots to make it as easy as possible to put it together.
Several had been sent to 2 different animation companies in Seoul and none were working.
I got nearly a week in Seoul, but only 2 half days to look around as it took so long to find out that it was 60Hz and there was a switch in the CCTV camera that needed changing if it wasn't running on 50Hz
I've wondered how people keep things straight in Japan. The country uses 100v (not 120v, though the outlets are the same as in the US), but what's worse is that it's 50 Hertz in eastern Japan and 60 Hertz in western Japan. (I think Siemens designed one end of the country and Westinghouse the other.)
Many years ago I did some work in Taiwan, where they had 110v and 220v in the same building. We had a 220v server, which was carefully plugged into a 220v socket. Problem was that no-one had noticed that the extension lead in the middle was only rated for 110v. It worked for a while....
I took on a project recently which served to show me how much I don't know about electrics. Out of curiosity, what's the failure mode of a cable like that?
I'd have thought that a higher voltage would mean less current, and therefore less heat created in the cable. Do you just get breakdown of the cable insulation under the higher voltage?
@My-Handle
Yes if the 220V appliance was pulling well below max current, then yes, a drop in voltage would pull more current but the 110V cable could be fine.
However...
If the machine was already pulling significant current (lets say maximum to make the point clearer) at 220V, a cable spec'd for the same current but at 110V would have significantly more power going through than designed. 100V cable would obviously get then hot, and depending on spec and manufacture of the cable, failure would be through either insulation breakdown, or the wire itself would effectively act like a fuse and burn out.
Have I got this right (ish ish), in absolute terms the cable is rated for power not for current... specifically for heat in the cable itself. And for insulation etc.
British mains cords kit have fuses in all the plugs, so all that happened when I used a 240 V, 5 A, extension to run an electric fan heater at 1 kW (4 A)... then one of my sisters, not well briefed, turned the heater up to 2 kW... is that the 5 A fuse in the extension's wall plug popped after a few seconds.
I may have to call BS unless the insulation was what failed. And most 120V wiring has insulation rated for at least 250V. Wiring is rated for current, not wattage. Which is why you can power a whole neighborhood off a high-tension wire that's often thinner than the drop from the transformer to an individual house.
Oh good, I thought i was going mad.
Surely a cable is a cable depending on it's current rating. In the original article is 'Power Cord' meant to be 'Power brick', in which case I can see why it would go pop?
A 110V cable would likely be thicker than a 220V as it has to handle more current for the device it's designed for (always amused by American kitchen appliance cords - like something out of Terry Gilliam's Brazil.
According to my experience, not necessarily.
Most 110V plugs are of the [ | | ] type, or grounded [ | . | ]
I residential buildings, the 220V plugs are for AC's mostly and are keyed [ | . - ], but in legacy engineer shops, you'll often see just RED versions of the 110V [ | | ] socket, which is somewhat disconcerting ;-)
That doesn't make any sense, wires aren't rated by voltage they are rated by amps. The more amps you need the thicker (lower number) wire gauge required.
You could carry 1200 volts over a standard US "120 volt" extension cord, so long as it didn't exceed its amp rating (typically 15 amps for consumer extension cords with the standard household NEMA plug)
You could carry 1200 volts over a standard US "120 volt" extension cord, so long as it didn't exceed its amp rating (typically 15 amps for consumer extension cords with the standard household NEMA plug)
At some point the potential would great enough that the electricity could jump between pieces inside the cable, although 1200V might not be enough for that. I have seen cables labelled with xV / yA, put that's probably more about the end of the plug than anything.
It reminds of a saying I just made up, "Everything is a conductor if the potential is high enough."
"You could carry 1200 volts over a standard US "120 volt" extension cord"????
Probably not. I would think 220 volts might work most times but 1200 volts is a bad idea.
In the US, most 120 volt wiring only has a 300 volts rating marked on the insulation. At least that's what my laptops AC cable says on it.
The insulation on extension cords is FAR thicker than what is required for wire in wall/conduit, because it has to hold up to various types of potential damage like being twisted/pulled/stepped on etc. followed by pets/toddlers biting it. It may be stamped with a rating for 300 volts, but it would work at a far higher voltage unless it is damaged.
Just compare to the thickness of insulation on the wires it is connected to at the receptacle and run to the electrical panel. That's far thinner carrying the same 120/240 volts compared to the nice thick insulation on extension cords, because it is doesn't undergo those stresses hiding in your wall.
To be grateful for the onward march of time and inevitable improvements that it can bring - namely, the 110v ~ 240v issue. Modern stuff having internal switching to prevent this kind of conflagration... That said I was always tempted to play with that setting disc on the back of my 70`s amp to see what happened when changed between the various voltages it supported (240, 220 & 110 volts). Being in the UK it was always set to 240 so I guess not much being the result.
(also I still don't get what advantages 110v has other than it being a lower number so looks more safe..)
Your comment prompted me to search a bit, and I found this article which has a sentence that can resume the issue :
The Pearl Street Station also provided DC at 110 V, considered to be a "safe" voltage for consumers, beginning September 4, 1882.
One has to admit that it is the United States that pioneered electrical distribution, based on the work of that guy who electrocuted elephants to cast doubts on AC, Thomas Edison. But then, it would appear that a Berlin company decided, in 1899, to switch to 220V because, apparently, distributing electricity at that voltage was cheaper and more efficient.
Europe switched, the rest of the world largely followed, and here we are now.
When my parents moved from Southend into London, the London Electricity Board was supplying us with 100V DC. Soon after, they announced that they would be changing to 230V AC, and that they would pay for any modifications to wiring, equipment, etc., that that would entail. My father went around buying up all the old 100V DC motors he could find and attaching them to every piece of hand operated equipment in the house. One day, I came home from school and found a long row of brand new 230V AC electric motors lined up along the front hall, biggest ones nearest the door, getting smaller and smaller as they were farther down the hall. The next several weekends were spent swapping all the old motors out and replacing them with the new ones.
As a general rule yes, but not entirely the case.
Very high currents can be survived with no ill effect if the voltage is too low to overcome the body's resistance, i.e. the amps can't get into your body. Do not try this but one can put clean dry hands on either terminal of a car battery (many of which can produce upwards of 600A) and not feel a thing.
Ultimate it's energy that kills, power (voltage x current) applied for long enough time.
> Your comment prompted me to search a bit, and I found this article which has a sentence that can resume the issue :
> The Pearl Street Station also provided DC at 110 V, considered to be a "safe" voltage for consumers, beginning September 4, 1882.
Battle between Edison and Westinghouse was not 110 vs 220, but DC vs AC.
Edison, a supporter of DC, demonstrated the lethality of AC by electrocuting stray dogs.
https://www.smithsonianmag.com/history/edison-vs-westinghouse-a-shocking-rivalry-102146036/
"One has to admit that it is the United States that pioneered electrical distribution, based on the work of that guy who electrocuted elephants to cast doubts on AC, Thomas Edison.
--Edison was a guy who was too stubborn to admit he was wrong about DC power. He may have marketed the first successful light bulb, which was admittedly the killer app for electricity, but Westinghouse I believe, (and to some extent Tesla) were the actual pioneers of creating the USA's electrical power distribution systems. And US homes also have 220V, it's just normally used only for large, high-wattage appliances. I'll admit that 220V for everything is likely superior, as you don't need wiring as thick to handle the 15 or 20A 110V (really 120V normally) individual circuits like you do in USA homes and businesses.
It's not "internal switching" as such, selecting 240/230/220 OR 110 like the little selector switch used to do, but "Switched mode", which is a method whereby internal capacitors are charged from the supply voltage by a controller circuit that measures the state of the DC supply and "switches" the supply side as required to "top up" the DC circuit. Thus the supply taps into the mains no matter what the supply voltage only so much as to keep the output regulated. They are happy to run off a wide range of supply voltages. These supplies make use of reference components for measuring voltage and current... reference components which can degrade rather rapidly under certain conditions, thankfully mostly failing safe rather than the other way around.
A 240/230/220/110 switch usually indicates that a large iron-core transformer is being used, and the switch changes which tap on the primary is used, or for 110 V puts two (to better handle the doubled current) primary windings in parallel.
Not all switched-mode power supplies have an active power factor correction (PFC) stage which can work with a large range of input voltages. The ones that don't have active PFC have a switch to change between the input capacitors being wired in parallel (for 110 V) or series (for 230 V); they will of course only be rated for 200 V or so as there's no point using larger and more expensive capacitors. 230 VAC rectified gives about 325 V. Electrons with an excitement level of 325 V are partying too hard to be contained by a 200 V-rated cap, and the magic smoke and sparks escape.
A friend who is a safety engineer gave me an answer I find very believable: the copper industry had a lot of power at that time. The lower voltage you use, the thicker cable you need to handle the higher current draw. If we ran on 220V, everybody could use less copper. That wouldn't line Mr. Shiny's packets, so it wouldn't be acceptable.
110V has zero benefits.
Like most things it is a historical curiosity. In the USA Eddison started using 110v DC for lighting from his own generators. 110v DC doesn't work well for transmission distance so you have to have lots of generators feeding the system which means that it scales really horribly.
Westinghouse (their main competition) imported AC generators and transformers from Europe, using high voltages for transmission (as we do now) and lower voltages for the last mile stuff. This scales very well.
Eddison promptly started losing horribly to the Westinghouse system which was more technically supreme than superior, and to try and retain market share he leaked stories to the media of how horribly dangerous high voltages were, that they would kill everybody who walked within a mile of them etc etc etc.
The upshot of which is that Europe picked what engineers thought was a sensible voltage (220v-240v) for the last mile transmission, and a panicked America picked the voltage that people reading newspapers had been told wouldn't kill people walking down the street near an electric pole (110v).
Many years ago we had a dud batch of auto sensing PC power supplies that were supposed to set themselves to whatever you connected them to......except every so often one would set itself to 110 on a 240v plug, so when you switched it on the fuse would blow with a nice "pop". Very entertaining first thing i the morning when people are half asleep......
This is anecdotal (because I'm too lazy to do the research), but a long time ago one of my lecturers who had been a Electrical engineer with the armed forces in the UK explained the following to the class.
AC is used principally because it is is very easy to transform between HT power lines running at 15+KV and the street power, requiring only a passive transformer with the correct windings to do the conversion (so yes much cheaper over all).
Additionally he mentioned that AC was safer than DC because in a AC jolt your muscles spasm so in accidental contact you will usually be thrown off the wire, which is why AC electrocution of dogs/elephants/humans looks so horrifying. In a DC jolt your muscles will clamp and so if it happened you where holding the live wire it was likely you would continue to hold the live wire and just cook. Apparently Edison was loosing more linesmen for his DC systems than others where with their AC systems and put a lot of effort into hiding this fact.
He also mentioned that the survival rate for 200+ AC mains was better than 115 AC mains because if you bridge your hands across 200+V the current across your chest (based on bodies internal resistance V/R = I) has sufficient amperage to stop your heart, which usually restarted after the power source was removed and if not CPR could be performed. At 115V apparently the current induced across the chest is more likely to cause the heart to fibrillate which will kills you and makes CPR less effective requiring a defibrillator to save you.
As indicated above I've been too lazy to do the research to verify these statements, but he was a very very good lecturer who knew his stuff so I've never had a reason to doubt it. I'm willing to accept correction from others who know more though.
Having moved house I needed to rebuild my small office. Nearly everything to be wired through a 'cooker switch'. I did lots of custom wiring to be clever and have eg. a dimmer control for my foot warmer in easy reach. One merry morning I switch on at the master and there's an almighty bang and a flash. Whoops! All off again and see which PSU has gone. I can smell 'electrical'. Sniff-sniff PC1. Possibly. Sniff-sniff PC2. More likely. It turns out that there isn't a trace of smoke on any PC PSU. After gingerly powering up the naked PCs they work fine. Suspicion turns to my custom wiring, but nothing there. Both screens are still working. Umm. Life returns to nervous normal when, a few days later, there's a repeat. Definitely a flash. Definitely electrical. PCs fine. Aha! Screens. I thought I could smell electrical so started a long job of dismembering a screen. Nothing to see and after the fuse was replaced all was working again. The oomph of the bang convinced me it must be a PC PSU so I ordered a replacement and held my breath each time I switched on. After a take everything apart, put it back together in the light of a couple of week's experience, I was tinkering with something else, connected to a different circuit via a 4-way. BANG! Hey! How did that happen? Then I saw it. A fine spray of soot and copper across the worktop. From a white cable. With a tiny black hole torn in it. This cable wasn't overloaded, twisted, bent, squashed, nailed, folded or otherwise maltreated; it had just decided after 20 years of use to short internally. Moral of the story: Bangs DO leave smoke stains but it's easy to fool your nose into smelling it when it isn't there. Odd.
Not always smoke stains. How about the ca 12V-rated electrolytic capacitor on a bench top power supply that can go up to 30 V ? Fortunately (a) it was only about 100 uF and (b) I was outside the room where that happened. Walked in to find a nice shower of confetti cascading down and a gibbering experimenter.
It's not just your white cables that can go short like that. At the beginning of December (just post-lockdown start) the cable 100metres or so down the roa did that. Standing on the road surface you could feel the pulsing under your feet. It also damaged the adjacent gas pipe, fortunately not as bad as it might have done.
I unearthed an old valve amplifier from a loft years ago still at school or (possibly VI form) that was just crying out to be powered up. This was in a steel box with the top 2/3 punched full of holes.
I plugged it in and switched on the huge great toggle switch. Lights glowed, valves started to warm up, everything look good....
Then keerrrrrboooooommm.
Crap and smoke absolutely everywhere and a truly awful chemical burning smell. House sockets all fused, everyone running around trying to figure out what had happened. Two very large physically and electrically (something like 10,000uf, about 6" tall and 2" diameter) capacitors had blown up, rupturing the cans and filling the place with the contents. It took weeks to get rid of the smell and tinsel from my bedroom.
The amp was quietly consigned back to the loft. It is probably still there even now 40 years later, just waiting........
Old electrolytics should never be just powered-on.
The insulator in an electrolytic capacity is actually a thin layer of oxide formed on the surface of the foil, and over time it degrades. As long as the electrolyte isn't completely dried out it can be reformed, after some physical checks to make sure they aren't leaking or bulging you need to gently apply a voltage, and increase it to the rated value while watching the current. If it has dried out the capacitor needs to be replaced, but at least you'll see that by the increasing current drawn before it gets to the point of going bang. It's hard to predict lifetime, it depends on temperature.
Transistors don't take kindly to capacitors failing, but a valve amp might well be OK once you've replaced the capacitors (and checked/replaced all the others).
"Two very large physically and electrically (something like 10,000uf, about 6" tall and 2" diameter) capacitors had blown up"
Power supplies often use electrolytic capacitors. A capacitor basically consists of two plates with insulation between them. The can acts as one plate of the capacitor and the roll of aluminium foil as the other. The aluminium foil is electrolytically oxydised, the resulting thin layer of aluminium oxide is nonconductive and acts as the insulator between the two plates.
If the equipment is never powered up then over time that oxide layer deteriorates so instead of a capacitor you now have a short :(. Apparently the best way to deal with vintage electronics which have not been powered up for a long time is to start by supplying them with a much lower voltage. That should allow the oxide layer to reform. Then you gradually increase the voltage (using a variac or something). So I'm told - haven't tried this. And if it did try it, it would be outside out of harm's way. (This probably only works with traditional linear power supplies, not with modern switching power supplies.)
Thank you for that post.
I have to say, I do not remember ever needing to check that my laptop's power cable was compatible with EU or UK power.
Of course, I know that a 110V power supply is going to die a quick death if you plug it into a 220V mains, but the cable ? It doesn't care.
So I really don't get that the cable is the cause of the whiteboard's problem. There has to be some other reason - maybe the cable was faulty, had a kink in it or something.
But I'm convinced that a cable that can handle 110V is not going to have much of a problem handling 220V. They don't make the metal wire thinner.
I was wondering the same thing ...
unless the whiteboard was accepting only 110V and there was supposed to be a transformer in between to take the 220 and downgrade it to 11 and with only the cable they fed it directly 220 ?
And yes, I have accidentally blown up a PC ones that was sent back to our office from a remote location that used 110 and I forgot to check the setting before plugging it into 220
but other than the prongy bits at the end I've never had an issue with cables ...
and I've had a few colleagues who moved from a 110V country to overhere, and they've all happily used plugconverters and extension cords without any of their electornic toys going bang
I did do not believe it was the cable that blew up. My guess is that the whiteboard in question was designed to only work at 110V (perhaps someone ordered the wrong one). Someone realized that at some earlier point and took the power cable so that it could not be accidentally plugged in to the 220V socket. Our regimized hero inadvertently bypassed that safety measure when he used his own cable.
My only question - Do South Korean 220V wall sockets have the same form factor as American 110V sockets?
Do South Korean 220V wall sockets have the same form factor as American 110V sockets?
According to the IEC’s world plug page, no — their wall sockets are for plugs of types C (“Europlug”) and F (“Schuko”). Note that South Korea is listed as running 220 V at 60 Hz.
North Korea, however, is given as “220V / 110V 50Hz / 60Hz A / C / F”, so apparently they have some proportion of ungrounded/unearthed sockets for type A plugs of North American (NEMA 1-15) or Japanese (JIS C 8303, Class II) form.
My first thought was "there was probably a reason why that device was disconnected in the first place".
I.e. it was already broken, but hadn't quite let out all of the magic smoke yet.
A little googling suggests that power cables used in 110V environments have a beefier wire gauge (because apparently there is only a single hot lead?). So it should have worked better than the cable it replaced.
But yeah, some of these stories sometimes feel like someone is blowing smoke up our .... :)
We had a client with a US parent company, at the time their software ran on a *nix machine with IBM InfoWindow terminals. So the shipped over a MUX, terminals and printers for us to use. They made us buy 240/120 step down transformers for every item. When I checked them.. every thing they sent had auto ranging 100-240V PSUs. That's a lot of transformers we ended up just stacking in the warehouse.
Icon - because that's what happened.
When I was young I was working for a small company that supplied hardware and software for the admin side of a niche(ish) market.
This was in the days before the IBM PC gained its place as the de facto standard for office computers and there were still a wide range of disparate platforms on which to run software. We supplied a computer called a Durango Star for the job - ran CP/M of a sort but that is not where the fun started.
As these machines came in from the good old US of A we also provided a hardware maintenance service. The Durango Star had a switched mode PSU built from descrete components so didn't care about the input voltage, which was a selling point I guess. The PSUs were prone to failure in two ways - failure of components due to quality issues and, we were to discover, a design feature where an internal power connector could be connected the wrong way around, applying huge voltages where they didn't ought to be.
The hardware engineers were always very careful to check which way around the connector was except one time - the software team (invcluding me) were in one room beavering away at ISAM code which was corrupting the databases on a random(ish) basis when our concentration was broken by an almighty bang from next door, the hardware workshop. Rushing next door, imagine our surprise to find the airborne insides of a couple of large electrolytic smothing capacitors, which had lost their integrity due to said power connector being connected incorrectly, and several stunned hardware enginners wandering around looking sheepish...
Two amusing tales from days gone by (where health and safety was not such a concern as it is today).
As a youngster in the electronics repair shop, we would sometimes amuse ourselves by charging up an enormous capacitor to the limit of the bench power supply of around 80V (2500 microfarad, 100V part IIRC). We would then clip one end of it to a metal plate and holding the other lead with insulated pliers, proceed to engrave rude things on the metal plate by keeping the lead at a distance across which an arc could form.
When I was in college, there was an enormous wirewound inductor encased within a Perspex cover and it had a blade switch.
One day, the instructor demonstrated an effect known colloquially as 'inductive kick'.
He moved the blade switch to supply DC to the inductor, then turned off the lights and moved the blade switch to remove the DC current.
There was a blinding flash of light and a sizzling sound; very impressive but I am not too sure how bad it was for the eyes as such a flash has quite a lot of UV.
Both things that health and safety inspectors might be aghast at today.
I used to work for a US-based Diagnostics business with an office in Germany, and had to fly over to set up & install a piece of lab kit that the US had shipped over for them to use. The analyser had a voltage switch, no problem, and the computer likewise. However the printer...... Long story short, the guys in the German office wanted a printer to use with the machine, and when I suggested that the cheap inkjet might not cope with European voltages the title was quoted to me. After the magic smoke gratefully escaped they acknowledged that the answer was, in fact, no after all.
Back in college doing electric engineering course, the Head of the department (a f**king idiot) was demonstrating in the power lab (high amp motors turning generators)
He set up the volt meter and amp meters the wrong way round, bollocked me (student 1st year) for trying to point out his mistake.
He fired it up and was confused due to no readings,(90V at 40+amps expected), instead of shutting down and checking he started switching connections at random.
I backed away to emergency stop button just in case, just as he almost gets hit with sparks going across connectors he's messing with.
(he seemed to have it in for me after that, he marked a test of mine as 0 correct, which was wierd as when I cross checked with other students was at least 80% correct, he refused to correct, until I went to principle in the break, he came back and immediately corrected it, I should have really continued with the complaint in hindsight)
Late 8os or thereabouts I bought my first flat in hackney.
It had been previously had the owner's aged mother upstairs and he'd created an internal stairway. Now converted back to two separate flats.
I came to change the light fittings and carefully isolated the ring.
All was fine until I came to do the hallway. Having done a couple of other rooms I could have been forgiven for not checking this one was safe.
Luckily my inner paranoid was feeling frisky that evening. Checked, glowed.
This one was still very much live.
He'd wired it so that it worked the light upstairs or something ( can't remember the details) as well as the hall, and used the upstairs supply. Luckily there was a taped off wire for my supply in there. I can't remember what I did with the upstairs supply.
Back in college doing electric engineering course, the Head of the department (a f**king idiot) was demonstrating in the power lab (high amp motors turning generators)
Ah, those were fun.
That sort of motor needs to be started gently, via a rheostat bank. It starts with a high resistance, and as the motor picks up speed and starts to generate back EMF you reduce the resistance until eventually it's running at full speed directly across the supply. In our lab that was 200v from very large lead-acid batteries. Lots of current available...
When the rheostat was moved to the end of its travel it was held in the "full speed" position by a solenoid, and when the power was switched off the rheostat released & dropped back to "off". Or at least, that was the theory. We had one rheostat that was stuck. A fellow student wired everything up and, not noticing or checking the rheostat, pulled the main power switch for his motor. With the rheostat stuck the motor was placed directly across the supply. These motors were about 4ft long, bolted to the lab floor in a solid steel frame, probably weighed several hundred kg.
I still remember the noise, an anguished howling screech, as this big traction motor went from rest to full speed in about 1 second. I saw it flex in the frame, smoking, and the cables (think car starter motor size) all sagged as they heated up, but to our (and the prof's) astonishment the fuses held and the motor settled down to run normally. I can't speak for the state of the unlucky student's underwear, but we all wanted to do it again. None of us dared to try, though.
Previous owners of my house (back in the 90's) wired up some kind of internal telephone system with those old style telephone sockets from the 70s with some kind of patching screwed to wooden sill under a window in the living room.
Couple of years back, started removing this cabling, traced it all back to where it went, including outside the house and round a wall and back in again. Looking at the main junction box couldn't find anything bar normal ring mains.
So merrily cutting cable with a pair of wire cutters, was fine. Pulled the cable through the ceiling (where it led into the attic), there was a flash, a bang and a black scorch mark where the cable came through and all the electric went off. Carried on removing all the cabling I could find in every room and in the attic and outside the house.
To this day, I cannot find at any point where it was actually connected to the mains or looked like it passed into a socket where it was connected to the mains and I pulled everything out.
I worked on my aunt's house changing a light fitting in the kitchen. Discovered through "sixth sense" that the idiots who had wired the house did ring circuits by taking the lives out of one fuse, running it around the house, then bringing it back to the DB and into a SECOND fuse block. None of the fuse blocks were labelled. One of them DID turn off the light though... but that was because the wiring in the rose had worked loose and one of the lives going out to the ring wasn't contacting the screw block properly and feeding live down to the switch.
Impossible to identify and isolate the entire fitting by switching MCBs off one at a time. It was only when I felt the hairs on the back of my hand stand up as it got close to a wire that I figured I'd best use the tester screwdriver on the bare copper end instead of the screw top. Lit up like a Christmas tree. I was just seconds and millimetres from getting a nasty shock.
I've had similar with stairs lights controlled by a switch at the top and at the bottom. The installers had clearly thought: there's an upstairs light and a downstairs light, so clearly it has to be wired into the upstairs fuse and the downstairs fuse. It was pure good luck I was standing on a ladder and gravity broke the connection when I discovered this.
I used to live in an upstairs flat (where the building had previously been 1 single house), when the property was converted a new mains supply was installed by the electricity board for the upstairs flat.
I never found out how (but assume a wiring cockup combined with 2 supplies on different phases) but if I switched the upstairs hall light on at exactly the same time as turning the downstairs one off there would be a big bang, tripped breakers for the lighting circuit and every single bulb that was on at the time would be blown.
Back when I was travelling often, I had the ultimate status with a certain hotel chain.... This usually got me a room upgrade (often to a suite), unlimited complimentary minibar and Club access. On a holiday in Malta, I went to the Club lounge for breakfast one morning, grabbed some cereal, put some bread in the toaster, not realising some toasters are less equal than others, and walked off. That turned out to be a big mistake. Fortunately, it was caught quickly when the fire alarms went off and the hotel was surprisingly forgiving.
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