Another Shocking Tale
This is one that should be told as a Lurid Work Story, but it's no myth: it happened about a week before I started at the company in question. I saw the scars, both physical and emotional, on the people who worked there.

As part of the apprenticeship I mentioned in "Hot Steel Suicide", in South Africa, I was seconded to other parts of the company, and this was the last such secondment, to a subsidiary on a different site. This was a company which used massive arc furnaces to smelt metals to produce specialised alloys. When all the furnaces were going at full whack - which was most of the time - the place used as much electric power as a medium-sized town (they said).

Slightly techie bit: the electricity comes in via 33kV (high voltage) lines, and is fed in to massive transformers (bigger than shipping containers) where it is stepped down to a much lower voltage (200-300V) but at a MUCH higher current. A 220V kettle draws around 9 amps, but the current going to each furnace was measured in hundreds of kiloamps, with solid steel beams as conductors (basically). The transformer power handling capacity was measured in megawatts (MW), and occasionally one would blow up spectacularly (but safely, since they were away from people).

So here's the scene: a furnace is offline, and a team needs to work on top of a transformer. They have safety procedures, and so the high voltage side is isolated, tested, and tested again. No-one's going to get shocked today. You'd think.

The problem was this: a welder, with an electric arc welding machine, is fixing a flaw on the low voltage side - those massive steel conductors I mentioned. And those are still connected to the transformer. So the low voltage from the welder gets stepped *up* to a high voltage, which is then fed in to the people working on top of the transformer. The current was fairly low, but it doesn't take much current to hurt people. One was killed, and three more suffered burns and injuries by falling off, including the supervisor.

I guess that's how safety procedures evolve: by trial and error. It did cast a shadow on my time there, made worse by my immediate boss having severe health problems and dying of cancer not long after I left. That and the sheer filth of the place. They actually hired me after my apprenticeship was over, but I lasted only a couple of years before I said "sod it" returned to the UK.
(Tsukemono, Sat 7 Sep 2013, 20:35, 22 replies)

if they were on top of the transformer
Where was the path to ground?

Not trolling. Genuinely interested in things electrical
(Frample Tromwibbler climbs an obstacle like old people fuck, Sat 7 Sep 2013, 20:40, closed)

Metal, Metal, Everywhere
The transformer case itself - made of metal and earthed.
(Tsukemono, Sat 7 Sep 2013, 21:11, closed)

Through the transformer casing as somebody fucked up the isolation.
Primary and Drain Earths should be applied to ensure that a: any accidental energising would result in a circuit trip, and b: any induced voltages (due to cables/busbars running near the circuit) would go straight to earth. Secondary to that the welder must not have used a proper earthing arrangement.
( parttimedogfish is a Born-Again Reincarnationist, Wed 11 Sep 2013, 17:52, closed)

It is quite ridiculous that safety standards didnt mandate the use of Direct Current for arc welding on transformer lines - as only AC would be stepped up like that. I mean obviously most welders are AC but that should have been seen coming.
(Carpe Cyprinidae, Sat 7 Sep 2013, 22:07, closed)

We wondered about that too ...
... but a DC welder would not have removed the danger entirely, since the DC current flow would not be continuous but spiky i.e. it would have an AC component.

The real solution is to earth the low voltage rails as a matter of course. Which is quick and easy to do, as opposed to isolating them, which would add more complexity and/or work to the procedure. As long as such grounding straps are removed afterwards ..!
(Tsukemono, Sat 7 Sep 2013, 22:26, closed)

Couldn't they just make everyone wear wellies?
( Happy Phantom has been to Hastings, Brighton, and Eastbourne too, Sat 7 Sep 2013, 23:05, closed)

Earth
Really? Welders need a return path. That either means that your "steel beams" and the welding machine had to be connected together, or they shared a common earth. In neither case could anything be fed back into the transformer to be stepped up.

So bollocks to that. Either you didn't understand what was happening or you're lying.
(ubergeekian, Sun 8 Sep 2013, 0:33, closed)

I'd have assumed the LV side of a transformer making a conversion of that magnitude would be fairly low resistance. Could be they were welding the nominally positive line with the return path through the coil to ground for some reason
(Carpe Cyprinidae, Sun 8 Sep 2013, 0:36, closed)

don't bother trying to reason with such blatant trolls, save yourself some time and report them to the law

( The Mock TurtIe ™ --- Thinks you are a cunt, on, Sun 8 Sep 2013, 0:56, closed)

Even then
the most the primary would see would be a fairly small bit of the welding voltage, which ain't high.
(ubergeekian, Wed 11 Sep 2013, 20:37, closed)

Being right is really important to you isn't it?

( edjogs Collared doves are shit., Sun 8 Sep 2013, 0:48, closed)

Yes
But then, I'm used to it.
(ubergeekian, Wed 11 Sep 2013, 20:37, closed)

( Happy Phantom has been to Hastings, Brighton, and Eastbourne too, Sun 8 Sep 2013, 0:50, closed)

lol
why don't you go all the way and change your name to Robert Killjoy-Silk
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Sun 8 Sep 2013, 0:51, closed)

( Happy Phantom has been to Hastings, Brighton, and Eastbourne too, Sun 8 Sep 2013, 1:03, closed)

oh look, it's another formulaic attempt to troll my posts with a link
yawn
( The Mock TurtIe ™ --- Thinks you are a cunt, on, Sun 8 Sep 2013, 1:57, closed)

( Happy Phantom has been to Hastings, Brighton, and Eastbourne too, Sun 8 Sep 2013, 10:12, closed)

Us dullards should stick together.

(s0ckpuppet logging out to reply to you if you're not careful, Sun 8 Sep 2013, 10:24, closed)

( The Mock TurtIe ™ --- Thinks you are a cunt, on, Sun 8 Sep 2013, 23:27, closed)

Really?
Why the hell would I make up something like this? If I was going to, I would make it less techie and more interesting. It was nearly 25 years ago, but it definitely happened.
(Tsukemono, Sun 8 Sep 2013, 11:38, closed)

Ignore him, he's an autistic troll.

( BraynDedd Natasha Kaplinsky's labia majora, Sun 8 Sep 2013, 12:37, closed)

Offhand?
I can think of about twenty seven reasons why you'd make it up. My "you didn't understand" offer is open as well.
(ubergeekian, Wed 11 Sep 2013, 20:39, closed)