It will be interesting to know if its on the supply side or the consumers side. I suspect that there will be some recriminations if it turns out to be on the racecourses side of the supply rather than southern electric's.
On Wed, 16 Feb 2011 12:13:12 +0000, tony sayer sprachen:
Well, you can't. The amp rating of a particular power supply is it's maximum.
The actual current is just volts / ohms. The resistance of a human / animal body is very variable and unpredictable.
But yes, deadliness is determined by current flow and time. But current flow is determined, from the electrical bit's point of view, just by voltage. It's unlikely a power supply would have a higher impedance than a person.
That's also why you can't have megavolts at yocto-amps. The impedance of the target person would bring down the voltage being supplied, until the reduced voltage gave a current the source could actually supply. Or put another way, til the relative impedances of source and target allowed it.
This is all in the case where we're electrocuting a human with a specific resistance / impedance.
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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." #
Quite - and whoever left it live probably buggered off long ago...
A recent episode of CSI Miami (made long before the Newbury horse deaths) used an under beach cable to knock off (as in electrocute) a mens volley ball team. One wonders where they got the idea from. Or did reality copy fiction in this case.
In article , greenaum scribeth thus
I think you misunderstood that. If there are not enough Volts to drive sufficient -current- through the resistance of the particular "circuit" then it doesn't matter how many amps you can supply. Hence the example of the very low voltage and high amp capacity. The other instance is high volts but insufficient current to do any damage...
Indeed it is..
As above sufficient volts and current availability..
Yes you have it..
We had this the other year, an olde cable stub kept shorting and blowing fuses, fuses replaced and all OK for a while, and finally it shorted out for good. A bod turned up with a very large short circuit relay device which took the place of the fuse in the distribution cabinet.
Quite spectacular, he had a hand held radio trigger gubbins where he could take cover and then fire the device which was some feet away. Upon contact the cables to it would leap up in the air and then as the relay tripped they would drop back to the ground!.
The next bit was very impressive. He has some gangers standing around where the cable went with their legs apart then triggered it and one of them pointed to a spot in the pavement and said "its there" sure enough they dug at that spot and there was an old cable that should gave been disconnected but hadn't been, and over time the land had been disturbed and water etc had got in hence the occasional short and then that would blow the shorted part open and over time it closed again and then blew part away until it made a very good job of it closed properly this time, and finally they were able to locate it!..
Seems they can feel the underground "bang" with their feet and the direction where it came from!...
There have been many instances where a lightning strike on a playing field has disabled players, sometimes just stunning them, sometimes killing them outright. They tend to take lightning storms a bit more seriously then what we do, they seem to have stronger ones there and more of them;!.
Hence there are several websites on that very matter in the USA...
On Wed, 16 Feb 2011 01:34:37 +0000, Andy Wade sprachen:
They still haven't dug it up yet? Don't they have shovels in Newbury?
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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." #
Tsk. You don't dig holes with a shovel.
when they undergrounded the 11KV supply here, if developed a fault. They isolated a loop and used I think TDR kit to pinpoint it to exactly outside my house. where it feeds my own personal substation yay!. anyway, they were not wrong. Water in a cable and massive charring when the diggers finally got down to it.
In part you do.
It may take only a very short duration pulse to 'stop' (fibrillate) a heart, especially if it comes at the right time, in the T-wave of the ECG. The current required to do this is less than would cause damage through electroporation. The reason that 50Hz (or 60Hz) AC current is dangerous, even at relatively low, non-burning currents, compared to DC, is that it exposes the heart to a long series of shocks, increasing the probability of one of them being at exactly the right time to induce VF. (AC will also pace the heart at a fast rate, increasing its susceptibility to VF for various reasons.)
Francis
Probably! (Glue-on horseshoes do exist, but they're generally for horses with iffy hooves and are usually, but not always [*] made of plastic.)
[*]Francis
It's ages since I heard that one - thanks for reminding me.
Nothing to do with thyristors or racehorses but ...
There was another amusing story monologue that I heard at about the same time - concerning someone who ended up in hospital after reaching for a hanky in his back pocket with the wrong hand, or something like that. Probably not Hoffnung. Anyone remember that one?
Francis
Inasmuch as carbon is the same thing as diamond, yes.
Francis
Conversely I've heard that a DC shock of the same voltage and current as the RMS AC equivalent can more dangerous because the muscles of the hand will contract permanently around the live object whereas with AC they will contract on one half-cycle and expand on the next half-cycle, increasing the chance that the victim will be able to pull his hand away.
But ideally you want to avoid the shock altogether. Having had a mains shock from the terminals in the power switch of a telly (turned off at the switch increas of the wall - blush!), I don't want to repeat the experience: even though it was just across either side of a knuckle, my whole arm was numb and tingly for about an hour afterwards.
I've heard the same, though I think it may be a marginal effect because at 50Hz most muscles will be pretty much tetanized (i.e. steadily contracting, not twitching). The fusion frequency is ~16Hz for slow twitch fibres and ~60Hz for fast twitch fibres, and most muscles have a mixture of slow and fast fibres.
Quite!
When I was 7 years old or so, I got a shock from the cooker main switch on the wall. I think my hand must have been wet. The racking spasms down the right side of my body were mercifully brief, but it's not something I would ever want to repeat!
Francis
Isn't the grip thing more down to the fact that all muscles can only contract thus they work in pairs and generally speaking the stronger muscle of the pair is the one making the grip not releasing it.
I've had a few minor belts off the mains, not to be recomended.
No.
Well, DC flowing through them (they only pass current in one direction).
There are also gate turn-off thyristors (GTO) which can also be turned off using the gate electrode, but the last time I used a thyristor was before GTO thyristors were invented, so I've never played with one.
They're much easier to blow up. A thyristor can only be On or Off, and in neither state is there scope for enormous power dissipation (although the GTO thyristors do have some more explosive failure modes). On the other hand, a FET is continuously variable beween On and Off, and in the half-On state, a tiny package measuring just a few mm² can generate 1000's of times the power dissipation you might have been designing for if intended for On/Off switching. FETs are also static sensitive.
We were somewhere around Barstow, on the edge of the desert, when the drugs began to take hold. I remember snipped-for-privacy@cucumber.demon.co.uk (Andrew Gabriel) saying something like:
"Sure, Sor, me and the lads will pull out that old bit o' cable for ye".
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