is 240v really that dangerous

[SimonH2]

I remember seeing a chap quite badly burned on the hand by touching some live three phase gear. It's not just the power to shock, the energy burns as well.

The is a chap locally who I went to school with, I never did get the full story (and some versions contradict), but as far as I can tell he was sent to do some work at a factory, someone else did the isolation and certified the installation as dead - but between that and this chap setting to work a generator kicked in. Then he went into the busbar box and got fried. Some versions say it was 11kV, but that doesn't fit with the rest of the story - I wouldn't have expected a factory that size to have an 11kV generator, and assuming it was setup correctly it should have had the ability to backfeed through the 11kV/415V transformer.
He's "quite badly" disfigured from the burns*, and apparently the surgeons who first treated him didn't expect him to survive due to the serious internal damage. Friends who know him better than I did say his personality was significantly altered as well.

* I've only seen his arms, neck, and face - I'm told that most of his body is just as scarred.


But back to the OP. I doubt if any of us who've worked (or played) with electricity haven't had shocks - petrol engine HT systems are good "fun". As pointed out, we're lucky enough to still be here. When you get that "wrong side of the threshold" shock, it's too late to change your mind and decide that perhaps safe isolation would have been a good idea

 

[Dave54]

I remember seeing a chap quite badly burned on the hand by touching some live three phase gear. It's not just the power to shock, the energy burns as well.

The is a chap locally who I went to school with, I never did get the full story (and some versions contradict), but as far as I can tell he was sent to do some work at a factory, someone else did the isolation and certified the installation as dead - but between that and this chap setting to work a generator kicked in. Then he went into the busbar box and got fried. Some versions say it was 11kV, but that doesn't fit with the rest of the story - I wouldn't have expected a factory that size to have an 11kV generator, and assuming it was setup correctly it should have had the ability to backfeed through the 11kV/415V transformer.
He's "quite badly" disfigured from the burns*, and apparently the surgeons who first treated him didn't expect him to survive due to the serious internal damage. Friends who know him better than I did say his personality was significantly altered as well.

* I've only seen his arms, neck, and face - I'm told that most of his body is just as scarred.


But back to the OP. I doubt if any of us who've worked (or played) with electricity haven't had shocks - petrol engine HT systems are good "fun". As pointed out, we're lucky enough to still be here. When you get that "wrong side of the threshold" shock, it's too late to change your mind and decide that perhaps safe isolation would have been a good idea

I've been out of industry for 30 years now, so I'm more than a bit rusty. The chap who had that burn had reached in to get something that had been dropped IIRC. It was 415V 3 phase there. Nasty burn on the hand, and a hell of a shock apparently, but nothing as bad as what you describe. As you say that suggests 11kV.

I worked in industry for nine years after my apprenticeship, and had really very little to do with the 11kV there. Certainly had nothing to do with it apart from switching on/off on occasion and winding the breakers in/out.

Surely if that guy was working on a busbar chamber, then it should have been isolated on the feed and distribution ends?
Also I have a vague memory of reading something about checking that there is no alternative means of supply like generators?
But accidents wouldn't happen if everything was exactly as it should be of course.

 

[conny]

Two lads I worked with a number of years ago where working on a bus-section distribution board.
They were working on the dead side with the busbars of the live section segregated by a board. Bobby G was working on the LV terminals in the front of the cabinet and Bobby N was working on the dead busbars. As Bobby N tried to loosen a 16mm bolt through the dead busbar his spanner slipped, knocke the barrier out of place and contacted the now exposed live bars in the adjacent cabinet. He was also steadying himself by holding on to the cabinet with his left hand.
415v across both arms/chest and a massive bang which blew Bobby G backwards out of the front of the cabinet.
Bobby N suffered severe burns to both arms, face, ears, neck and head. His hair was burnt back across most of his head, lost his moustache, eyebrows and eye lashes.
He spent months in Leeds General burns unit before being transffered back to Merseyside to continue treatment. He had to wear stockinette protectors on his hands and arms for months and whilst in Leeds also had to wear a plastic face guard.
In one respect he was lucky. He survived. There were times when he wished he hadn't because of the disfigurment he suffered.

 

[ross94]

And I thought we got some stupid questions in the Plumbing Forum but this OP should be a candidate for the Darwin awards!

Oh well... let natural selection take its course.

tbh, I am beginning to think this thread is a bait.

its got to be, I hope op is just messing about. god forbid if he is genuine about this.

 

[Dave54]

And I thought we got some stupid questions in the Plumbing Forum but this OP should be a candidate for the Darwin awards!

Oh well... let natural selection take its course.

tbh, I am beginning to think this thread is a bait.

its got to be, I hope op is just messing about. god forbid if he is genuine about this.

If this thread makes just one person who thinks "It only tingles" aware of how nasty electricity can be, then it'll have served a useful purpose.

 

[SimonH2]

The chap who had that burn had reached in to get something that had been dropped IIRC. It was 415V 3 phase there. Nasty burn on the hand, and a hell of a shock apparently, but nothing as bad as what you describe.

Then I think you may be thinking of a different case - the chap I know really did have serious burns and life threatening internal injuries.

 

[Dave54]

The chap who had that burn had reached in to get something that had been dropped IIRC. It was 415V 3 phase there. Nasty burn on the hand, and a hell of a shock apparently, but nothing as bad as what you describe.

Then I think you may be thinking of a different case - the chap I know really did have serious burns and life threatening internal injuries.

Yes it's a different case. I can see I made it look as if I might have been talking about the same one. I wasn't. The one I said about happened in the Midlands.

 

[Adam_151]

I've seen a colleage nearly killed whilst working on a heating system in a pub. He had properly isolated and proved the circuit dead only for a thermostat fed from a different circuit to click in and bring one of the wires live. It touched the palm of his hand causing his muscles to contract so he was unable to let go of the wire. He suffered horrendous burns and it scared the living sh-t out of me. It's something I'll never forget.

Yet the whole industry still holds the safe isolation procedure up as a holy grail of safety.... when the above proves it far from infalliable. What happened on the circuit your colleage was working on is very difficult to prevent unless you isolate at the main switch of the installation, which of course is impractical in just about everything other than domestic. One must therefore always bear in mind the risk of it happening and try and work in a way that minimises risk if it does

 

[ericmark]

I was reading about Nikola Tesla and his demos to show how AC was safe. Read battle of the currents. It seems frequency is also important as to what frequency he used I don't know. However I do know on 20 meter band RF burns take an age to heal.

To my mind the experts have worked out safe limits with AC it's 50 volt however still working on road salting wagons I have had a good belt from just 24 volt DC. As to back EMF from relays and like that can be very nasty.

We have I would guess all played tricks with meggers and impulse mags. However these can also back fire even when there is a limit to the power they can deliver. I walked into a motor vehicle workshop and saw the impulse mag under the bench with a wire to the vice. I was young and daft so I lent on the vice and a guy walked up and started to chat. As I saw his hand go down to the impulse mag I placed two fingers of my hand on the back of his neck. I real thought I had killed him. OK he was trying to shock me in fact I did get a shock, but he sank to the ground and lay their with a waxen face and did not move.

He gradually recovered and when every one saw he seemed OK I got clapped for teaching him a lesson. But it was me who got the lesson I never played again giving people shocks. We have no idea how electric shocks will affect others and little idea of how it is affecting us. Any electric shock means a visit to hospital and hooking up to their meters before we know if any harm done or not. Today both of us would have been required to visit hospital likely I would as an apprentice likely got away with it, just a telling off, if they had worked out what I had done, other guy would have been dismissed as gross industrial misconduct today.

 

[RF Lighting]

I've seen a colleage nearly killed whilst working on a heating system in a pub. He had properly isolated and proved the circuit dead only for a thermostat fed from a different circuit to click in and bring one of the wires live. It touched the palm of his hand causing his muscles to contract so he was unable to let go of the wire. He suffered horrendous burns and it scared the living sh-t out of me. It's something I'll never forget.

Yet the whole industry still holds the safe isolation procedure up as a holy grail of safety.... when the above proves it far from infalliable. What happened on the circuit your colleage was working on is very difficult to prevent unless you isolate at the main switch of the installation, which of course is impractical in just about everything other than domestic. One must therefore always bear in mind the risk of it happening and try and work in a way that minimises risk if it does

The other big danger is borrowed neutrals. Again you can carry out safe isolation and as soon as you split two wires you're working on an energised circuit without realising it.

I used to work in an old mill which had a 100A SP&N supply to each floor. Where the PILC supply cable entered the floor there was a DP isolator.

The passenger lift in the mill had a TP only supply. At some point a light had been installed in the lift car using a phase from the lift supply and a neutral from the top floor in the mill pinched out of one of the DBs.

If you threw the DP isolator on this floor to do any maintenance work all the lights went out and the sockets stopped working, but in reality every line and neutral conductor were being back fed from the lift light and sat at mains potential.

If you didn't prove dead, or worse still the item you were working on had a broken CPC then not even the standard procedures for proving dead would prevent you from working on a very dangerous installation.

I know a lot of people dislike volt sticks but I always have one in my pocket, and use it as an addition to proving dead after I've cheched with my two pole testers.

 

[PBC_1966]

The other big danger is borrowed neutrals. Again you can carry out safe isolation and as soon as you split two wires you're working on an energised circuit without realising it.

Another neutral issue related to isolation for working here in the U.S. is the neutral in a multiwire branch circuit (i.e. a 3-wire circuit, typically used to save cable by feeding two heavier 120V loads in the same location or to wire a series of 120V receptacles alternating on each pole etc.).

At one time the NEC permitted each side of the circuit to be fed via its own completely independent single-pole breaker. That's fine if the person realizes that it's a multiwire branch circuit at whatever box he goes into (which he should, but that's another matter) and turns off both breakers. But if he just turns off the breaker for the particular outlet, not realizing that the neutral going through that box may still be carrying current from the other pole, and opens that neutral, he can be left with 120V across the opened white wires.

Today, the NEC requires that such circuits be fed either by a double-pole common trip breaker, or if fed by single-pole breakers that a handle tie be installed so that it's impossible to turn off only one side of the circuit when isolating for work.

 

[ross94]

I wonder what has happened to the op, we have not heard of him since, wonder if he is lying "stone dead" after experimenting with 240v such as turning on the kettle or the induction hob then grabbing on to the live and neutral and see if its still gives "little tickle"?.

I think I am being silly and getting a bit carried away.

bet he is reading all of this and having a little chuckle to himself. tbh I think this guy is taking the ****.

 

[JohnW2]

I wonder what has happened to the op,... bet he is reading all of this and having a little chuckle to himself. tbh I think this guy is taking the ****.

That's obviously quite possible, but I have to say I get concerned by the number of people I hear saying things like he did - i.e. they have had a few 'tingles' or minor shocks when touching 240V (usually when fairly well insulated from earth) and therefore wonder 'what all the fuss is about'. It may do some good to expose such people to a few grizzly anecdotes.

Kind Regards, John

 

[Adam_151]

.

If you threw the DP isolator on this floor to do any maintenance work all the lights went out and the sockets stopped working, but in reality every line and neutral conductor were being back fed from the lift light and sat at mains potential.

.

Theres a school where a SPN board had been replaced. The biggest MEMshield 2 board they could grt was 16way which wasn't big enough so someone ha used two boards. I can't remember what the exact arrangement was, but each board had its own DP isolator, alhough the second board I believe was controlled by the isolator on the first as well. But the neutrals had been mixed mixed up. If you threw the main switch on the second board, everything would become live through a neutral which had been opened. This repeated in 2 or 3 places in the building! I assume it had been done by the same guy whole had replaced the lights. Conduit as CPC. Conduit enters new fitting via plastic end cap. No attempt to connect to it. Or the rows o through wired fittings (different room, different fittings). The new ones were shorter than the old ones, so there was a 20mm gap in the conduit, the only earth path was through the metallic ceiling grid they were fixed to!

 

[SimonH2]

I used to work in an old mill ...

That reminds me of a tale told by a mate who's been a sparky all his working life.
He had a job to do on a machine in a textile mill, and it had the old switch fuses with no lock-off facility. So he switched off the supply to the machine he needed to work on, hung up the "do not switch on - sparky working" notice on it, and went back to the machine. Tester says it's live - so back to the switch room to find the notice on the floor and the switch back on.
Repeat and same thing happens again.
On the third attempt, he switches off, hangs the sign, and hides out of sight - sure enough, a machine operator comes in, throws the sign on the floor, and switches it back on. My mate tells that he punched him hard enough to put him on the floor - and quickly the machine operator is sacked and thrown off the site, and my mate was escorted off the site for his own safety
Turns out that each supply serviced several machines, and as they were all on piece rate the other operators didn't give a **** about the sparky - only that they were losing production while the power was off.

Going further back, my Dad used to tell stories from when he was a young jobbing sparky. One job he got called to was to a motor driving a line shaft under a bench of sewing machines. He expected to find it buried in a box full of lint (it was in a box at the end of the bench) - but found it spotlessly clean and polished The sewing girls told his they always cleaned it as part of the Friday afternoon cleanup, "especially that shiny brass bit" - yes, they polished the commutator with the motor running For the youngsters, back in prehistoric times, a lot of motors were open and the commutator and brushgear were all exposed.
This was also before the trolley busses got replaced by diesel in Nottingham. He said you could see by the ammeters in the substation when a bus was going up corporation hill (without belching black smoke !).

Ah, he had lots of tales to tell. Another wasn't electrical, it was about not being under anything suspended. He said they were moving a large heavy motor, and at one point he had his legs under the motor, braced against something and pulling it across. When they'd done, he came to unscrew the eyebolt they'd lifted the motor with - and it just snapped in his hand. He always says he was lucky not to lose his legs that day.

It's stories like that that stick in the mind, and every so often I'm about to do something and a little voice tells me to stop and have another think.