How accidents happen - Page 1
Forum section: electronics / general

author: Mr. Scram
author_rank: Super Contributor
timestamp: February 03, 2018, 09:51:34 pm
content: Today something happened to me I always deemed quite unlikely. While hanging a lamp, I made sure to take every precaution I could think of, partly because someone inexperienced was helping me and I wanted to show what you can do to work safely and protect yourself. After mounting the hook to hang the new lamp from and making sure the wall lamp switch was in the off position, I turned everything off at the breaker panel again, put on some rubber gloves and peeled the tape from the wires to connect everything up. It was at that point that someone poked his head around the door and told us it was odd how the lights were still not on, as he just turned things on at the breaker panel again.It turns out he had arrived, concluded the lights weren't working and started messing with the breaker panel close to the doorway right away. It seems he didn't quite understand how the breakers work, as he just flipped the big switch and you need to flip the smaller switch too to get things powered up again. Of course, making sure the light switch in the room I was working was actually turned off and wearing gloves should have saved my bacon regardless, but I can't believe how unbelievable unlucky that timing was.I never figured it to be very plausible for someone to turn up and to mess with the breaker panel at those exact 60 seconds I was touching the actual wiring, yet that's exactly what happened. Obviously, my mistake was not to put up a note at the breaker panel. It might be missed in the dark, but it's a lot better than nothing. I blame myself for that, as I had consciously told myself to do that yesterday. Unfortunately the panel can't be locked, so that was not an option. I hate to think I might have been more careless if I would have been on my own. Even if the power had been turned on properly, there was still more needed for things to go awry, but I consider it a close call regardless. Another unseen problem like the light switch being wired backwards or not being properly double throw could have easily defeated another precaution. I actually felt stupid for putting on gloves, but it turned out to be more sensible than I ever expected. I thought I'd just share the experience as an example of how quickly things can devolve, to learn from my mistake and that taking every precaution isn't a stupid thing to do at all, even if you do feel you're being overly careful.Have you had any close calls?

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 03, 2018, 10:06:04 pm
content: Many states' worker health and safety legislation requires locking remote breakers to prevent just this sort of occurrence. They make little devices that mount directly on the breaker's lever which accommodate a small padlock. "Lockout tagout" are the key words.I was once wiring a light when a fellow and otherwise very conscientious electrician helpfully turned it on so I could see better. Human nature is a fault sometimes.

author: Jeroen3
author_rank: Super Contributor
timestamp: February 03, 2018, 10:30:39 pm
content: I was working with an inexperienced guy at a generator. I showed how you could make sure no voltage was present by:- Put meter in fixed range.- Verifying your meter works at a known source (nearby mains socket)- Measure what you're going to be working on.- Verifying your meter works at a known source again.You'd think these are all extra steps are useless and your fluke will always read correct, right?Read on...When the work of replacing equipment was done, we'd turn the thing back on and we had the meter attached to measure a few things.The generator had synced to the grid, and we were measuring exciter voltage, which is DC. But it didn't show any voltage. Which was weird, because there was current, diagnostic of the controller said there was current, and the generator was outputting power. We had measured the exciter to be a few ohms, so that was ok too....I tested the fluke on the mains socket, and yes it said 230V... I connected it to the exciter again... 0V. Exchanged clamps... 0V...Then I walked to the 24V starter battery, probed it and it said 0V. Which can't be since the thing had just cranked with those.Walked to the control panel, probed 24V UPS line. 0V...Turned out the test lead had an internal failure, go figure. Open for DC, a capacitor for AC. Yeah, I was very happy I showed him the correct method to verify something is off.Job wasn't completely safe, we couldn't ride the breaker out since a heavy pallet tank was blocking it.

author: igendel
author_rank: Frequent Contributor
timestamp: February 03, 2018, 10:32:12 pm
content: I noticed once, in an electricity cabinet (or however it's called...?) in the university I studied in, there was this big frightning sign saying "don't touch any of these, someone may be working on the electrical system elsewhere in this building and you might kill them." I still think they should have put there a physical lock of some sort, just in case...

author: tautech
author_rank: Super Contributor
timestamp: February 03, 2018, 10:41:54 pm
content: Quote from: Mr. Scram on February 03, 2018, 09:51:34 pmYep and now I pull the fuse or MCB and put it in my pocket.Just make sure NO other spare fuses or MCB's are lying around for someone to plug in.

author: TerraHertz
author_rank: Super Contributor
timestamp: February 03, 2018, 10:43:33 pm
content: If the master breakers can't be physically locked off, and tagged "do not operate", then the next best thing is to tape a piece of paper over the breaker, with a big warning note, like "Working on wiring, do not turn on".Still not going to protect you against malice or stupidity.The Fluke Voltalert non-contact mains voltage sensor things, that look like a fat pen, are very useful. But be aware you have to run them along cables, since with the twist of internal wires, at regular intervals the earth wire shields the electrostatic field, and the Voltalert will see nothing. Also some cables are shielded.A convenient way to check the Voltalert is actually working, is to rub the tip on your sleeve. The electrostatic charge generated is enough to trigger the Voltalert to flash.Back before Voltalerts existed, I was at a factory disconnecting a bit of gear, with the factory owner present. A 415V 3 phase building wiring cable needed to be cut. He took me to the circuit breaker board, showed me which breaker it was, turned it off.Back at the cable, I still made sure to use a well insulated pair of cutters, and not touching anything else while cutting it.BANG! One pair of cutters with a chunk blown out of the jaws.He'd been wrong about which breaker it was.Lesson: Never believe anyone about stuff being 'safe.' Check it yourself before touching anything.

author: abraxa
author_rank: Frequent Contributor
timestamp: February 03, 2018, 10:46:03 pm
content: Quote from: Mr. Scram on February 03, 2018, 09:51:34 pmI certainly do hope you gave that person a mouthful about how he almost killed you because of his stupid actions. Did you?

author: rsjsouza
author_rank: Super Contributor
timestamp: February 03, 2018, 10:57:29 pm
content: Quote from: abraxa on February 03, 2018, 10:46:03 pmDepending on the place (residential), that would be my question as well. I would be fuming...After a shock (and there were many in my life) I always get pissed and think the outlet or wiring are staring at me and singing: " Na-na-na-na-na-na! I gooooot you!"The other thread below is also interesting...https://www.eevblog.com/forum/chat/electric-shock-experiences-for-those-still-alive/

author: Mr. Scram
author_rank: Super Contributor
timestamp: February 03, 2018, 11:16:55 pm
content: Quote from: abraxa on February 03, 2018, 10:46:03 pmNo, as I was still processing what happened. Looking back I mainly disappointed myself by not at least putting up a note. I even planned on doing so, but simply forgot. Locking things up would be even better and something to look into next time. I should expect others to act in the least desirable way possible. I can get mad and blame him, but the next time someone else comes by and the very same thing could happen again. Blaming someone else won't unelectrocute you. I'm responsible for my own safety.

author: abraxa
author_rank: Frequent Contributor
timestamp: February 03, 2018, 11:24:16 pm
content: Quote from: Mr. Scram on February 03, 2018, 11:16:55 pmWell sure, I agree. However, not being told the lesson that can be learned here means he'll do it again somewhere else. I mean - who turns on circuit breakers without even checking why they're off in the first place?

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 04, 2018, 01:53:06 am
content: If you're doing this on any kind of a regular basis, you have your own set of locks, tags, and adapters for the most common types of disconnects. In the end, there is no one who can be responsible for your safety but yourself.That's fine at work -- but you might not think to need these at home (or be able to use them, if the breakers or panels are different)!A good example illustrating this, at low voltage and with a happy ending (no zaps).Tim

author: Vtile
author_rank: Super Contributor
timestamp: February 04, 2018, 02:44:27 pm
content: Quote from: Jeroen3 on February 03, 2018, 10:30:39 pmThis is the exact reason every CAT rated meter should be shipped with lowZ / low impedance functionality working in every range ... No exceptions in CAT III + CAT IV rated handheld multimeters.

author: Marco
author_rank: Super Contributor
timestamp: February 04, 2018, 04:59:26 pm
content: Quote from: blueskull on February 04, 2018, 01:45:08 amIffy system to have to rely on, there's no real alternative there ... but when possible physical locks are better. Needing to get a boltcutter is a better hurdle than a warning on a computer screen.PS. actually on second thought it's obviously not necessary. Automate it such that the lineman has his own PDA on which he has to sign off before the operator can do jack shit. Overruling that should require management level clearance (on a technical level, not just procedurally). The digital equivalent of the personal locking and tagging which is common for more local work (ie. a box holds all the keys for the locks on the equipment, all workers put their personal lock on the box so those keys are unavailable until all workers have returned).

author: Jeroen3
author_rank: Super Contributor
timestamp: February 04, 2018, 07:27:40 pm
content: Quote from: Vtile on February 04, 2018, 02:44:27 pmFluke 87V does not have LowZ. You can get a small resistor module though.

author: NiHaoMike
author_rank: Super Contributor
timestamp: February 04, 2018, 11:25:57 pm
content: The worst are illegal unfused taps:It was also pointed out that whoever installed the fuse box mixed up input and output so the fuses are always live!

author: james_s
author_rank: Super Contributor
timestamp: February 04, 2018, 11:31:12 pm
content: The statistics are out there, accidents are not uncommon although they are normally the result of carelessness.An electrician was electrocuted at the place a friend of mine worked. I don't have many details but he was a licensed professional, fell dead in the spot he was standing.

author: rbm
author_rank: Regular Contributor
timestamp: February 04, 2018, 11:46:19 pm
content: My in-laws are having renovations done to their house. As part of that work, there is demolition going on. The crew doing the demolition work turned off the breaker panel before cutting into wiring in the kitchen. The removal of electrical outlets consisted of shipping them off the end of the wires. When they had finished, they had several wires laying on the floor with just clipped ends. They turned on the breakers again and left.Unknown to me that they had done this, I was walking around the kitchen area making measurements for the cabinets and accidently kicked the loose wire on the floor. It contacted a piece of metal around the door frame and huge sparks leap up. This was a 120V 20A circuit, live with open ended wire; they hadn't even bothered to tape or wire-nut them. Slovenliness leads to accidents.

author: nctnico
author_rank: Super Contributor
timestamp: February 04, 2018, 11:51:18 pm
content: Quote from: Mr. Scram on February 03, 2018, 09:51:34 pmNope. When working at a chemical plant I have learned the LOTO procedure. Lock-out tag-out. At home this comes down to locking the closet with the breaker panel and putting the key in my pocket.

author: Mr. Scram
author_rank: Super Contributor
timestamp: February 05, 2018, 07:41:34 am
content: Quote from: nctnico on February 04, 2018, 11:51:18 pmI would have locked the cabinet or room is that was an option. Unfortunately, it's not.

author: Paul Moir
author_rank: Frequent Contributor
timestamp: February 05, 2018, 08:19:57 am
content: Now you know it is.

author: Mr. Scram
author_rank: Super Contributor
timestamp: February 05, 2018, 09:50:39 am
content: Quote from: Paul Moir on February 05, 2018, 08:19:57 amThat's not locking the cabinet or room.

author: Someone
author_rank: Super Contributor
timestamp: February 05, 2018, 10:26:48 am
content: Quote from: Mr. Scram on February 05, 2018, 07:41:34 amWhen locking is not possible (for various reasons) licensed professionals I've worked with have tagged without locks and then disconnected the downstream connection at the breaker (inside the panel) for additional assurance. Don't trust anyone else with your safety.

author: rrinker
author_rank: Super Contributor
timestamp: February 05, 2018, 04:56:31 pm
content: All the warnings and safety procedures in the world can;t save you from stupidity (or yes, malice, if someone is really out to get you). The rules should be similar to railroad rules (and to my understanding, they generally are) - the person working sets the lockout, and ONLY that person is allowed to remove it (railroads tag equipment being worked on with a blue flag - only the person who placed the flag is allowed to remove it). Of course, "is allowed to" is just a rule, there's nothing physically there preventing some other idiot from walking up and just doing something. Keyed lockouts, with each person having a unique key? Then someone would finish a job only to find out they've lost their key and now a 2 hour job takes 6 hours while waiting for a locksmith or someone with a spare key.Bottom line - what can you do? Nothing is foolproof, the fools just get better every time you try. Acceptable risk is about as good as it gets - reasonable and accepted safety procedures, if followed, should at least mitigate risk to an acceptable level. Does that mean it's still possible for someone to get hurt? Yup.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: February 05, 2018, 05:40:07 pm
content: In some ways the older consumer units were safer. The modern DIN rail ones with saddle clamps have very poor clamping force on the cable tails, and I've seen cases where even after firm tightening the copper strands rearrange themselves (a bit like powder in a tin settling) and the tail just falls out of the receptacle. That never used to happen with the older semi-enclosed wire fuse types.For anything over 16mm sq you really need a tommy bar on the screwdriver for enough torque to get a reliable clamping, and then you're risking breaking the plastic case of the MCB/isolator.It's also possible to inadvertently put the tail over instead of under the saddle. It will still seem like you are tightening the clamp, but of course the tail isn't secured. If it's touching the clamp then everything will work until it gets a bit oxidised, then you have a fire. An electrician in a hurry is very likely to leave one or two like this. Stupid design.Seen one case where an all metal CU was fitted as a replacement for a supposedly 'old and dangerous' unit, and a fire started at a loose connection. The front was metal but held closed by a plastic twist catch, which promptly melted allowing the front to open. The fire did a fair amount to damage to the room. The 'old and dangerous unit' had been there since before WW2 and never gone on fire. The 'new and IEE compliant' unit lasted two months before reducing itself to a pile of slag.

author: jolshefsky
author_rank: Regular Contributor
timestamp: February 05, 2018, 05:41:54 pm
content: I've been accused of being daft for, after checking that everything is off on a mains circuit, I shield myself as best I can in the situation and drop a screwdriver across all the wires. If I did everything correctly, nothing happens. If not, I get a dazzling display that I didn't die that day.

author: Jeroen3
author_rank: Super Contributor
timestamp: February 05, 2018, 06:03:55 pm
content: Quote from: IanMacdonald on February 05, 2018, 05:40:07 pmHave you never heard of ferrules?Miniature Circuit Breakers take solid core wire, stranded with ferrules or fork terminals (where the busbar slides in).

author: phil from seattle
author_rank: Super Contributor
timestamp: February 05, 2018, 07:24:13 pm
content: I believe the lock outs are required in the US, at least in my area they are. But, every electrician I've ever had at my house doing interior stuff has worked with the power on, even to the circuits they were working on. I asked 2 of them about it and they both laughed - too much time going back and forth. I asked them if they had insurance...

author: james_s
author_rank: Super Contributor
timestamp: February 05, 2018, 08:53:14 pm
content: I've occasionally been guilty of doing electrical work on energized circuits, but I would never recommend anyone else do so. For residential work it's usually sufficient to place a note on the panel, and tell anyone in the house that you shut off the circuit to work on it. Even then I try to treat any circuit as energized even when I know it isn't, and I always verify. More than once I have encountered junction boxes containing more than one circuit fed by more than one breaker, that's not supposed to happen but you never know what you'll find in older buildings.

author: calexanian
author_rank: Super Contributor
timestamp: February 06, 2018, 12:36:36 am
content: Sounds like Murphy almost paid you a visit. Here in Yankee land where you cant really get one of those lockout devices jammed into a breaker I will either use tape and a note for minor repairs, or will just physically remove the breaker if it is a longer project. I also will tape the light switches themselves down to help the reflex of switching on lights while walking into a dark room.

author: TerraHertz
author_rank: Super Contributor
timestamp: February 07, 2018, 11:31:36 am
content: Quote from: IanMacdonald on February 05, 2018, 05:40:07 pmGood practice when wiring panels supposedly involves giving each wire a good tug after tightening the clamp. To check for that case of not having actually clamped the wire. Also going back after a few minutes and tightening them again.Since I bought a ferrule crimper, I use ferrules for all mains wiring connections, if at all possible.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: February 07, 2018, 11:36:14 am
content: Quote from: TerraHertz on February 07, 2018, 11:31:36 amI recently made the mistake of buying some terminal strips that basically consist of two screws in a tube per position. Not even a spring guard thingy, let alone a proper rising cage clamp. There's enough space either side of the screw to fit a 24 AWG wire. Just because it clamps, doesn't mean >14% of the strands are even tied in.We don't have to use ferrules over here, but I have used them, and they are quite nice.Tim

author: fubar.gr
author_rank: Unknown
timestamp: February 07, 2018, 12:50:06 pm
content: Quote from: Jeroen3 on February 05, 2018, 06:03:55 pmI almost always use ferrules when using stranded wire, because they make neater connections and protect the strands from breaking.But I don't think they are really required. You can use bare stranded wire directly on MCBs if you like.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: February 07, 2018, 01:29:44 pm
content: All of this is a reminder that safety precautions don't prevent accidents. They only reduce the likelihood. There is always danger.

author: IanMacdonald
author_rank: Frequent Contributor
timestamp: February 07, 2018, 03:21:41 pm
content: Quote from: Jeroen3 on February 05, 2018, 06:03:55 pmHave you never heard of ferrules?Miniature Circuit Breakers take solid core wire, stranded with ferrules or fork terminals (where the busbar slides in).Can't say I've ever seen ferrules used here. Besides, the older fuse carriers never HAD this problem. Also, heavy current stranded cables always terminated reliably to a 'Henley' block without excessive force. Fundamental problem is a crap design which has become entrenched as a standard, and hence we now can't easily get rid of it.

author: ahbushnell
author_rank: Frequent Contributor
timestamp: February 07, 2018, 07:33:06 pm
content: I guess thats why they use lock out tag outSent from my SM-G930V using Tapatalk

author: nes999
author_rank: Contributor
timestamp: February 08, 2018, 09:05:02 pm
content: I think anyone who has worked in a trade long enough will have had a close call.I do maintenance for a dog obedience facility. One day I come in and notice the light that was always left on was off. I check it out it needs a ballast.u I talk to the owner and he wants the whole fixture changed. Since this buildings wired up like a bowl of spaghetti I pull the main to be safe. I should mention now this building's ceiling is just foil covered insulation.I go to remove the fixture and before I know it there is a spark show. It is arcing to the insulation. So needless to say the main does not control that light. Luckily nothing was hurt but my ego.This building used to be used during WW2 for maintaining tanks and whoever wired it up clearly was drunk. Nothing is easy at that place.Sent from my VS988 using Tapatalk

author: rob.manderson
author_rank: Regular Contributor
timestamp: May 13, 2018, 01:10:28 pm
content: Years ago, when I used to repair TV sets in peoples lounges, if I had to work on the mains input side (replace power switches etc) I would unplug the set and put the power plug in my pocket. If the customer even noticed they'd look puzzled until I explained that this way I *knew* the power wouldn't suddenly be applied when I least expected it.

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 13, 2018, 03:05:54 pm
content: The other Problem is when People dont speak the Language who get spoken in the Country.I on daily base I have to deal with many People who life here for over 20 Years and dont able to have an fluent conversation with.The problem get even worse when Kids who are born here in the Preschool the cant ever speak one word German.So in the later Days the fail in School to because the didnt understand anything.And when the get some Job what happened than? ->

author: oldway
author_rank: Super Contributor
timestamp: May 13, 2018, 04:54:15 pm
content: Always check the absence of voltage on the 2 ranges DC voltages and AC voltages ....I almost died because I did not respect this precaution.On a busbar where only DC power was to be found, I checked with my multimeter that there was no DC voltage.When I wanted to connect the cables, I took a violent electric shock that made me fall 2 meters away.Checking done, there was 220V AC on the DC busbar and my (Fluke) multimeter was indicating 0V with 220Vac when it was on the DC range.

author: German_EE
author_rank: Super Contributor
timestamp: May 13, 2018, 07:11:17 pm
content: Not all accidents are electrical and even if you follow best practice Murphy will get you.Eight years ago I was climbing an elevator shaft and I was using the correct safety equipment including a climbing harness as it was an 80m shaft. Suddenly one of the rungs of the ladder I was climbing gave way as a weld failed, and this failure occurred at the exact moment I had disconnected my safety harness so that I could transfer the shackle to the next mounting point. I fell 6m onto the roof of an elevator car which then gave way and I fell a further 2.5m to the floor of the car.In the accident investigation my climbing gear was checked and it was fine, so was the hard hat that fell off as I descended down the elevator shaft. Nothing could have found the faulty weld on the ladder apart from either an x-ray or an ultrasound and in the 1970's when that ladder was made people didn't check that sort of thing.Due to injuries received I'm now retired from the elevator industry and the only lasting injuries are to my back and leg which means that I walk with a limp. The insurance payout was substantial but I would rather be fit and healthy.Murphy missed one thing though. I fell to the right of the ladder and landed on the elevator car roof. If I had fallen to the left of the ladder I would have dropped about 50m to my death.

author: KE5FX
author_rank: Super Contributor
timestamp: May 13, 2018, 08:30:54 pm
content: Quote from: evb149 on February 03, 2018, 11:04:29 pmI agree this is common, but I've never agreed with it, or even understood it. How does the meter know the voltage isn't alternating? How does it know I'm not measuring AC at 0.01 Hz? Many DMMs don't specify a lower frequency cutoff in AC mode. Without such a specification, they should read all the way down to DC.A straightforward, intuitive implementation of an AC voltmeter is simply a DC voltmeter with a bridge rectifier. Who asked the manufacturers to include a high-pass filter, and why?QuoteThat I can understand. In DCV mode, I expect the meter to display average voltage, integrated by either an LPF in front of an ADC or by a mechanical meter movement.

author: VK5RC
author_rank: Unknown
timestamp: May 14, 2018, 10:42:58 am
content: @German-EE, I am not sure if you call that whole event lucky or not!Some quick back of the envelope calculations suggest you hit that lift at 40km/hr or so! Ouch!I ride a push bike quite a bit and was 'tripped up' once by a small dog while I was going about 50km/hr but I had quite a few metres to grind to a halt so dV/dT wasn't too bad!Robert

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2018, 10:59:04 am
content: One of the major systems I developed and support at the office is for "CoHE Inspectors". CoHE = Control of Hazardous Energies (not just electrical, but pneumatic, chemical, mechanical, etc.) We have hundreds of workers who have special training and annual re-certification to inspect employees to work on equipment to ensure that they know where all the breaker switches, cutoff valves, etc. are for each kind of equipment.LOTO (Lock-out, Tag-out) is the method used to physically lock-out a breaker (or valve, etc.) to prevent others from re-energizing the system, AND to personally identify the person who applied the lock, and what is being done and the timeline or scheduling, etc. They even put the photo of the person on the tag to personalize it because their life is at stake here. But preventable accidents still happen where people don't apply the proper preventive measures.

author: Jeroen3
author_rank: Super Contributor
timestamp: May 14, 2018, 11:23:49 am
content: Quote from: German_EE on May 13, 2018, 07:11:17 pmI don't have certs for working on heights, but I have seen the harnesses of co-workers. And these have two clips you're supposed to interleave.Considering elevators today are covered with control boxes, sensors and metal framework, you're lucky.

author: CJay
author_rank: Super Contributor
timestamp: May 14, 2018, 01:07:25 pm
content: I was taught very early in my career when I was working occaisonally for a jobbing electrician that you always pull the fuses/breakers and keep them in your pocket because there's always someone who might try to 'help' by refitting or resetting them, I have been asked a couple of times 'where are the breakers' by clients which may or may not have been a 'near miss' if they'd not been in my pockets..On stuff at my site if you've not got a lockout kit with you when you're working then I will personally escort you off site and make sure you don't get to come back.

author: Mr. Scram
author_rank: Super Contributor
timestamp: May 14, 2018, 01:12:03 pm
content: Quote from: CJay on May 14, 2018, 01:07:25 pmThere's inevitably someone who will know where to find spare fuses sooner or later.

author: Rerouter
author_rank: Super Contributor
timestamp: May 14, 2018, 02:21:03 pm
content: Yep, been there recently, locked and tagged a circuit breaker, so someone tried to turn it on, could not, overlooked the tag, figured it was jammed, went off to bunnings and began replacing the thing! unlicensed aswell.There reaches a point where you wonder about becoming a layer 2 sparky just so you can rip the feed fuses.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: May 14, 2018, 04:24:43 pm
content: I have to admit I have installed lamps quite a few times without cutting the current, it can be done ~ easily. Sure it's more risky but it also forces you to be much more cautious and careful...We have 220 volts here, I have accidentally touched live wires a few times and I'm alive and well, but in the US you have only 110 volts, right? Is that really enough voltage to kill somebody in a second?

author: Mr. Scram
author_rank: Super Contributor
timestamp: May 14, 2018, 04:35:02 pm
content: Quote from: GeorgeOfTheJungle on May 14, 2018, 04:24:43 pmYes. Only less reliably.

author: bob225
author_rank: Frequent Contributor
timestamp: May 14, 2018, 05:01:01 pm
content: Its not the voltage that kills its the current, Any domestic supply is enough to kill, let alone some one going across 2 phase of a 415v 3 phase supply, that melted the galv 100x100mm channel and main board - This was due to the telecoms engineer not waiting for the spark to put in a spur for there equipmentThe bloke survived with 3rd degree burns and life changing injuries - It took them weeks to get rid of the smell and rewire a 90% complete building, The repairs alone cost £40-50K back in the early 2000's

author: Lord of nothing
author_rank: Super Contributor
timestamp: May 14, 2018, 05:06:06 pm
content: Quote from: GeorgeOfTheJungle on May 14, 2018, 04:24:43 pmNo.

author: Mr. Scram
author_rank: Super Contributor
timestamp: May 14, 2018, 05:22:32 pm
content: Quote from: bob225 on May 14, 2018, 05:01:01 pmOh dear, saying it's not the voltage but the current inevitably leads to people tumbling over each other to explain why it is and isn't true.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2018, 05:24:07 pm
content: Quote from: bob225 on May 14, 2018, 05:01:01 pmYeah, that argument has been going back and forth for decades, but that statement of the issue is far too simplistic.Many of us have vehicles with batteries capable of 100s of amps. Yet when was the last time you heard of someone being electrocuted from a car battery? (Except of course for those ridiculous movies where they "torture" people with a car battery and jumper cables.)QuoteYes, because there is enough VOLTAGE to punch through your primary dielectric, your epidermis. Why do you think they charge up defibrilator paddles to 100s of volts?OTOH, if you have some conductive probes near your heart, it takes very low power (a few volts and milliamps) to affect your heart rhythm. That is why internal pacemakers can operate on small batteries for many years.

author: bob225
author_rank: Frequent Contributor
timestamp: May 14, 2018, 05:31:06 pm
content: Quote from: Mr. Scram on May 14, 2018, 05:22:32 pmThen you have AC vs DCsorry I must not troll, the story is true tho, I was on a building site the day after it happened installing a 4th remote keypad

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: May 14, 2018, 05:48:34 pm
content: Quote from: Mr. Scram on May 14, 2018, 04:35:02 pmBah, 110 must be tickles, compared to 220V :-) I once checked with a variac to see at what voltage it starts to feel dangerous but I've forgotten.Sweat is a danger though, that much I recall very well.

author: Tedro
author_rank: Unknown
timestamp: May 14, 2018, 06:03:35 pm
content: Quote from: GeorgeOfTheJungle on May 14, 2018, 05:48:34 pmPretty much. I have been shocked a few times by accident here and there. It is different each time and just depends on your body position and how you are grounded an or footwear. Sometimes its just a tingle when you come across a frayed wire in the wall or extension cord... to the knock the wind out of you.... whoa how did I end up on the ground type. Yes it is 110v-120v phase to neutral but we do have 220-240v phase to phase in the domestic setting. In the commercial setting I deal with 208v for most outlets and 277v for lighting and for those I don't take any shortcuts and extra careful. Most of what I work on is 208v.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2018, 06:22:49 pm
content: Quote from: GeorgeOfTheJungle on May 14, 2018, 05:48:34 pmBecause it dramatically lowers the resistance of your primary protective dielectric (the epidermis outer layer of your skin).That dielectric jelly they use for defibrillators (or EKG terminals) is just a more viscous version of sweat.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2018, 06:36:51 pm
content: Quote from: GeorgeOfTheJungle on May 14, 2018, 05:48:34 pmBigClive did an on-camera evaluation of shock levels. But then BigClive is an old sparky, so he probably has built up some immunity.https://youtu.be/wR6g38Pxwog

author: Gyro
author_rank: Super Contributor
timestamp: May 14, 2018, 06:39:33 pm
content: Quote from: Richard Crowley on May 14, 2018, 06:22:49 pmI suppose that means, the more nervous you are (sweaty palms), the more you have to be nervous about!

author: metrologist
author_rank: Super Contributor
timestamp: May 14, 2018, 06:59:53 pm
content: Quote from: Mr. Scram on February 03, 2018, 09:51:34 pmI read somewhere there are no such things as accidents...Some houses have hot wired to the lamp before the switch...

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2018, 07:12:49 pm
content: Quote from: Gyro on May 14, 2018, 06:39:33 pmIsn't skin conductivity one of the things that are measured by a polygraph ("lie-detector") machine? (Or a Scientology "E-Meter"?)

author: taydin
author_rank: Frequent Contributor
timestamp: May 14, 2018, 07:26:51 pm
content: Quote from: GeorgeOfTheJungle on May 14, 2018, 05:48:34 pmI get zapped by 380V every now and thenBut most of the time it's with just one hand and no other body part having good earth contact. So, it's usually something between light tickling to sudden pulling away my arm and hitting it somewhere, and then moaning about the pain of the impact.One time, I had 380V across index finger and middle finger, and I had to stop doing what I was doing until my hand "reset" itselfBut I agree with you, trying to prevent somebody from turning on electricity can go wrong in so many different ways. It's much better to take precautions so that when you touch the live wire, the risk will be limited. For example, wearing isolation gloves, wearing isolated boots, and MOST IMPORTANTLY, NEVER work inside an electrical cabinet with both hands inside it.

author: fourtytwo42
author_rank: Super Contributor
timestamp: May 14, 2018, 07:51:42 pm
content: I had an interesting experience many years ago in the back of a telco rack cabinet with a large mdf (main distribution frame) block having about 50 or so 80Volt telegraph circuits passing through it bolted low down on the left rear upright, as this is "low voltage" it was completely uncovered.I was actually working on a large winchester disk (14 inch variety) further up the cabinet and trying to get a good look inside at the head positioner with a mirror, it was very cramped and difficult to see what I wanted so I kept trying different positions untill my left ear made contact with all the rows of terminals on the mdf block!!!!!!80V isnt so bad on the hand but woww the effect it had on my ear was shocking, my head immediatly retracted sideways at high speed only to crash into the opposite cabinet vertical in the process crushing my right ear (guess it saved my skull)

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 14, 2018, 08:05:06 pm
content: At least here in North America, the statutory limit for "Low Voltage" is 48V.I have seen step-by-step telephone exchanges implemented with Strowger Switches. The outer wall was lined with 24 huge two-volt (lead-acid?) cells, each as big as a small refrigerator or a storage cabinet. Connected in series they formed the 48V battery that supplied the exchange (and all the connected telephones). I believe they were capable of sourcing many hundred amps of current. Tales of Crescent wrenches (BrEnglish: adjustable spanners) being evaporated upon contact with the current.

author: GeorgeOfTheJungle
author_rank: Super Contributor
timestamp: May 14, 2018, 10:36:17 pm
content: Quote from: Richard Crowley on May 14, 2018, 06:36:51 pmMr. Crowley, that's a cool vidjeo, thank you very much.I wonder how much more current would that have been with the same ~ 50 volts but when one's sweaty. IIRC most standard RCDs come calibrated for 30mA, I'd hope that's the "safe" limit before the heart stops/may stop beating.BigClive should have chosen the current path through his body from the *right* hand to the feet, not to the left hand... the way he's doing it his heart is in the circuit. Many service manuals tell you that: when poking inside a live device your left arm in the back and use only the right hand.

author: CatalinaWOW
author_rank: Super Contributor
timestamp: May 15, 2018, 01:03:43 am
content: There is no current or voltage which cannot cause death if it finds the right path through the body, the right timing and the right susceptible person (or maybe those rights should all be wrongs). But it does become extremely unlikely at lower voltages and currents, in dry conditions with healthy individuals. It is sort of like the golden BB that shoots down an airplane. It can happen but isn't the first thing anyone should worry about.

author: JohnnyMalaria
author_rank: Super Contributor
timestamp: May 15, 2018, 02:00:03 am
content: Volts jolt, current kills! So there

author: jmelson
author_rank: Super Contributor
timestamp: May 15, 2018, 08:21:50 pm
content: Quote from: Richard Crowley on May 14, 2018, 05:24:07 pmYes, I thought for a LONG time it was impossible to get a "shock" from 12 V. But, last year sometime I touched a board that had 12V power on it, and must have squeezed it hard enough that a little pointy bit of solder pushed through the dead layer of my skin, and I got a very noticeable jolt out of it! I was quite surprised by this! I checked that spot and there was no detectable sign of pierced skin at all.Jon

author: Seph.b
author_rank: Regular Contributor
timestamp: May 15, 2018, 08:32:54 pm
content: Why are capacitors at low voltages dangerous?I get that they can dump their current really fast, but lets say the cap on a starter motor, I have always heard it can shock you. If it is only at 12v how is it any different than the battery?

author: tautech
author_rank: Super Contributor
timestamp: May 15, 2018, 10:16:52 pm
content: Quote from: Seph.b on May 15, 2018, 08:32:54 pmThere's no cap on a starter motor only something that some might think looks like one.It's the solenoid and the energizing coil in it can bite.....when the energizing current is removed.The phenomenon is called back EMF and all magnetics when switched exhibit this behavior.It is 'managed' when required with reverse biased diodes and/or snubber networks.

author: Seph.b
author_rank: Regular Contributor
timestamp: May 16, 2018, 12:59:15 am
content: Quote from: tautech on May 15, 2018, 10:16:52 pmThanks. I thought the little cylinder on the side of motors like that was a big cap and that is what caused the danger.I am familiar with the back EMF on coils, I use a lot of relays and maglocks in my job, I just didn't put 2 and 2 together.

author: Richard Crowley
author_rank: Super Contributor
timestamp: May 16, 2018, 02:07:44 am
content: By "starter motor" we are assuming you mean something from a 12VDC vehicle. Indeed, the thing on the side is the solenoid which pulls the pinion gear into position to turn the flywheel, and closes the massive contacts to put 100s of amps into the motor.However on many motors powered from AC mains, there is a "lump" on the side which IS a capacitor. A cap used for starting and/or running the motor depending on what kind it is. It seems quite possible that one of those capacitors (especially the ones used only for starting) could carry a charge even after power has been removed. Always short out large capacitors before fooling with them, including measuring them.

author: SL4P
author_rank: Super Contributor
timestamp: May 16, 2018, 01:59:20 pm
content: First rule. Don’t trust anyone elseSecond rule. Second guess yourself.ALWAYS.

author: T3sl4co1l
author_rank: Super Contributor
timestamp: May 16, 2018, 11:12:13 pm
content: "The first principle is that you must not fool yourself – and you are the easiest person to fool." - FeynmanTim

author: The Soulman
author_rank: Super Contributor
timestamp: May 16, 2018, 11:39:05 pm
content: Quote from: Seph.b on May 16, 2018, 12:59:15 amIgnition coil? Very dangerous.