How accidents happen

[Jeroen3]

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.

Have you never heard of ferrules?
Miniature Circuit Breakers take solid core wire, stranded with ferrules or fork terminals (where the busbar slides in).

[phil from seattle]

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...

[james_s]

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.

[calexanian]

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.

[TerraHertz]

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.   

Good 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.

[T3sl4co1l]

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.   

Good 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.

I 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

[fubar.gr]

Have you never heard of ferrules?
Miniature Circuit Breakers take solid core wire, stranded with ferrules or fork terminals (where the busbar slides in).

I 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.

[CatalinaWOW]

All of this is a reminder that safety precautions don't prevent accidents.  They only reduce the likelihood.  There is always danger.

[IanMacdonald]

Have you never heard of ferrules?
Miniature Circuit Breakers take solid core wire, stranded with ferrules or fork terminals (where the busbar slides in).
[/quote]

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.

[ahbushnell]

I guess thats why they use lock out tag out

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[nes999]

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.



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[rob.manderson]

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.

[Lord of nothing]

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? -> 

[oldway]

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.

[German_EE]

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. 

[KE5FX]

What a meter will display when you hook it to a DC voltage when it is locked on a ACV measurement setting depends on the meter but "0VAC" would be a correct AC measurement.

I 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?

Conversely locking it to DCV and measuring an AC source might well read "0VDC" as well.

That 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. 

[VK5RC]

@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

[Richard Crowley]

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.

[Jeroen3]

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 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.

[CJay]

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.

[Mr. Scram]

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.

There's inevitably someone who will know where to find spare fuses sooner or later.

[Rerouter]

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.

[GeorgeOfTheJungle]

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?

[Mr. Scram]

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?

Yes. Only less reliably.

[bob225]

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 equipment

The 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