Re: C4 Racing from Newbury - 2 horses *electrocuted*

[tony sayer]

In article , Francis Burton scribeth thus

And I wonder what do they hold the Ally hoss shoes on with then?..

[Basil Jet]

The current rails in third rail railway systems are nowadays made of aluminium, so the insulating effect of the oxide layer is not important.

[The Natural Philosopher]

hooves are not conductive. Shoes attach to hooves. Its the frog that is in contact with the ground..

[Tim Downie]

conductivity values.

Tim

[Felicity S.]

That is so, thanks again to Andrew for the information.

Yeah, though to be fair, the rest of the media are pretty daft too.

Fliss

[John Rumm]

Voltage is a bit of a non issue in this case. Its the magnitude of the current and duration that will largely dictate the level of injury along with the general health and state of the victim. Obviously higher voltages make it easier to push the current through the body, and high enough ones make possible severe injury from follow on effects like arc flash.

[John Rumm]

Closely followed by an article on unexplained power cuts in a near by village? ;-)

[Andy Wade]

:-)

Meanwhile the following, posted in the IET wiring regs forum sheds some light, and raises the question of why a long-disused cable was still energised...

"A statement from Newbury said the racecourse was waiting for the outcome of Southern Electric's investigations, but managing director Stephen Higgins confirmed the likeliest possibility was the disused cable had been damaged, possibly by recent verti-draining, a turf maintenance procedure where spikes up to 18 inches long are used to aerate the soil and reduce compaction."

"Higgins said: "We've looked at drawings that are 40 years old and we've established that, before the 1992 grandstand was constructed, there was a cable potentially in that location."

[greenaum]

On Tue, 15 Feb 2011 18:06:00 -0000, "Mortimer" sprachen:

Was that one of the initial criteria?

I ask because it seems pretty stupid using such a marginally specced component. Surely variable mark/space includes 100:0. Even 95:5 must have been pushing it for the component.

Also... don't thyristors stay switched on as long as they have enough voltage across them? Or was it AC flowing through them? I'm sure you'll have known this at the time, but wouldn't a simple transistor / FET have been better?

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"hey let's educate the brutes, we know we are superior to them anyway, just through genetics, we are gentically superior to the working class. They are a shaved monkey. If we educate them, they will be able to read instructions, turn up on time and man the conveyor belts, sorted." #

[greenaum]

On Tue, 15 Feb 2011 16:58:25 GMT, [e-mail] (greenaum) sprachen:

In fact thinking about it, isn't pure aluminium oxide the same thing as ruby?

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"hey let's educate the brutes, we know we are superior to them anyway, just through genetics, we are gentically superior to the working class. They are a shaved monkey. If we educate them, they will be able to read instructions, turn up on time and man the conveyor belts, sorted." #

[Mortimer]

You've got me wondering now: was it a thyristor or a FET? Not sure: it was about 25 years ago and I can't remember. I agree: it was stupid to be given a device that was specced right on the borderline and which wasn't tolerant of error conditions such as under-spec input voltage, over-spec load current or failure of the switching circuit. I dare say we could have built in extra protection into the design, but I remember that component cost was one of the design criteria.

[The Natural Philosopher]

Depends. If its feeding a transformer then you cant got to 100% as there is then no AC.

You might well be modulating over a much narrower band of mark/space ratios.

That's why it sounds like it might be an inductive load,

[Chris J Dixon]

I remember once reading a test report written by one of my colleagues.

They had built a prototype railway rolling stock dc chopper based on a string of thyristors. The assembly was placed on a substantial metal bedplate in the test area. It was connected to the power supply through a water fuse. This consisted of a plastic bucket filled with water, having a couple of submerged cable connectors and a thin wire between them. For safety, the bucket had a wooden lid with a heavy weight sitting on it.

When the inevitable fault occurred, the fuse blew with some force, creating a waterspout which lifted the lid high in the air. Unfortunately, on the way back down, the heavy weight was faster then the wooden lid, and it wedged itself between the cable connectors, re-making the circuit. This would have been bad enough on its own, but with all the water sloshing around on the bedplate, the supply was now both shorted and earthed.

I believe it took some time to get supplies restored, and there were no intact thyristors left.

Chris

[Mortimer]

Sounds like it was caused by the same Sods Law fairy that caused the chain of events in Gerard Hoffnung's story about the barrel of bricks being hoisted up the building.

The thought of water near an electrical installation sounds like an accident waiting to happen...

[tony sayer]

The volts is the most, or most important part as you can have Mega amps at say 1 volt thats not, well unless its connected perhaps to electrodes buried in the brain, going to have much effect through the average Joe or Horsey.

Course you can have Mega Volts at a yoctoamp and thats not really going to have an effect either..

The matter is a combination of volts, the current capacity of that source. The Resistance of the connection to the victim and the electrical source and the resistance of the victims skin and the path of the current..

In the case of a Human from one leg to the other is less dangerous than from hand to hand which has the Heart etc in the path.

Course sufficient volts across whatever member of the body can cause debilitating effects and heating burning and possibly death...

It seems to me that in this case there must have been quite a voltage gradient across that ground either from a source that had the "other side" of itself earthed elsewhere, or possibly two conductors a distance apart and the flow was across the ground. Course we'll see what the official line is from those investigating..

[tony sayer]

In article , Tim Downie scribeth thus

Not Steel nails then?..

[Chris J Dixon]

Indeed, but the characteristics of a water fuse, crude though it sounds, actually make it very good for semiconductor protection, and a great deal cheaper than the equivalent cartridge fuse, which could easily cost as much as the device it protected.

Chris

[The Natural Philosopher]

Er no.

Beause of te resistane of te hman tuissues, there is an intrinsic relationship beween the volts and maps.

The long and te short of it is that whilst internally teh volts make lill and teh aps will burn, its the amps through that count, as these deliver the volts to te tiossues.

DC amps tend to kill by burning, AC amps by heart stoppage.

You cant GET mega amps through the body without serious volts..

Exactly.

Ditto.

I would estimate 50-100 volts across the front hooves would stop a racehorse dead in its tracks, if the ground was damp. The frog is fairly sensitive a bit of skin. Lie the palms of yer hand..

[tony sayer]

Thats the same as what I wrote above!..

You've been reading too much Westinghouse -v- Edision;!..

Yes as I said..

Any chance of a new spull chucker for the new year;)...

Wonder if anyone did any research on that;?.

Not like poor old Topsy the elephant;(.

[John Rumm]

True, but once you have "enough" voltage to get a noticeable current flowing (which in this case would probably be anything in excess of 50V) it does not make much difference how much you have beyond that - be it

50, 240, 400, or 11kV they could all drive enough current to kill.

Indeed, and that is a common daily occurrence for humans with static discharges etc anyway.

You seem to have slipped into the same trap you set for me ;-)

You will see much the same sort of effect as with a large current flowing to an earth spike etc - e.g. if the ground is uniform in type and conductivity, then a roughly circular area of voltage gradient radiating from the live point. 10V/ft would certainly be possible from a

240V cable I would have thought and over the length of horsey that would be (and obviously was) "enough" volts.

or not in all likelihood.