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In message et, Dave
Liquorice writes
On Thu, 03 Apr 2008 20:31:30 +0100, Charles Ellson wrote:

Whether you get thrown away or hang on more likely depends on which
muscles are affected

Aye all muscles work in pairs and one is normally stronger than the other.
Think of the bicep to bend your arm at the elbow and triceps to straighten
it. If the current is stimulating the stronger muscle you end up being
"locked on".

and/or whether being thrown away is actually the result of a reflex
reaction to a shock that might not actually be life-threatening.

Being thrown across the room is again a function of massively stimulating
the muscles, you involuntarily throw yourself across the room.

Been there and done that. It was a small room about 12' X 12 and I was
sitting at a bench on onside when I caught mains from the back of a
toggle switch. Apparently I pushed my self away from the bench so hard
that I hit the wall on the far side of the room. I don't recall a lot
about it, apart from being scared stiff for a second or so as I realised
what was happening. I woke up sitting on the floor, colleagues reckoned
it was quite spectacular!!



--
Bill

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On Sat, 05 Apr 2008 23:59:50 +0100, Bruce Fletcher (Stronsay, Orkney)
wrote:

Test if a wire is live by touching it to the BACK of the hand. The
muscle action is then to throw your hand away

Better still, test with a meter!

A meter can be misleading if it has a high impedance, as many modern
meters do. It'll measure voltages induced into the wire that are not
actually there if you apply even a small "load".

--
Cheers
Dave.

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On Sun, 06 Apr 2008 02:33:53 +0100 (BST), "Dave Liquorice"
wrote:

On Sat, 05 Apr 2008 23:59:50 +0100, Bruce Fletcher (Stronsay, Orkney)
wrote:

Test if a wire is live by touching it to the BACK of the hand. The
muscle action is then to throw your hand away

Better still, test with a meter!

A meter can be misleading if it has a high impedance, as many modern
meters do. It'll measure voltages induced into the wire that are not
actually there if you apply even a small "load".

In that case it will still show _at least_ the possible voltage that
contact might be made with even if the available current is minimal.

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On Thu, 3 Apr 2008 08:55:44 +0000, Stimpy wrote:

On Thu, 3 Apr 2008 07:42:49 +0000, Bill Again wrote

Reminds me of a time, hundreds of years ago, when I was about 10, and my dad
was repairing the electric iron. He had it in bits, looking for why it
didn't get hot any more. After he had put it back together he plugged it in
and while he was putting his tools away, asked me to touch it. Being
extremely naive I assumed that he wanted to know if it was getting hot or
not. So I touched it. "No. it' still cold", I said. "Oh, but you have sports
shoes on, take one off", he said. I really couldn't imagine how this was
going to affect my appreciation of how hot or cold the iron was, but I took
a shoe off and felt the iron again. "Zappaaloo !!!" I wasn't thrown across
the room, I simply couldn't let go! Dad pulled the plug out of the socket,
and more in frustration than sorrow, complained that obviously the iron
still wasn't fixed.

All this is true, whatever that means.

I guess it means that you quickly gained a *real* appreciation of what
electricity can do - and you've remembered it all these years!

My grandfather (RIP, but not of electrocution) in the United States used to
test a light socket by wetting his finger and sticking it into the socket. As
he was wearing rubber-soled shoes, and took care not to ground himself
elsewhere, he only got a tingle.

I wouldn't recommend it as a fool-proof method.
--
Chris Hansen | chrishansenhome at btinternet dot com

Kevin: "I'm a atheist and I don't want a pervy priest saying any last rites
over me!"
Bob: "Cross-posting top-posters go straight to hell anyway ..."
from alt.obituaries

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On Sun, 06 Apr 2008 03:28:47 +0100, Charles Ellson wrote:

A meter can be misleading if it has a high impedance, as many modern
meters do. It'll measure voltages induced into the wire that are not
actually there if you apply even a small "load".

In that case it will still show _at least_ the possible voltage that
contact might be made with even if the available current is minimal.

Only a *possible* volts and volts only jolt, it's mills that kills.

As the source impedance is so high the moment you try to take any current
all the voltage is dropped across the source impedance leaving naff all
across the "load".

--
Cheers
Dave.

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On Sun, 06 Apr 2008 03:28:47 +0100, Charles Ellson wrote:

On Sun, 06 Apr 2008 02:33:53 +0100 (BST), "Dave Liquorice"
wrote:

On Sat, 05 Apr 2008 23:59:50 +0100, Bruce Fletcher (Stronsay, Orkney)
wrote:

Test if a wire is live by touching it to the BACK of the hand. The
muscle action is then to throw your hand away

Better still, test with a meter!

A meter can be misleading if it has a high impedance, as many modern
meters do. It'll measure voltages induced into the wire that are not
actually there if you apply even a small "load".

In that case it will still show _at least_ the possible voltage that
contact might be made with even if the available current is minimal.

This is why the serious 'sparkies' carry analogue meters and 'test
lamps'.
Digital Meters can read apparent high voltages that were induced by
induction from near by cables. Analogue meters tend not to do that - they
pull more power from the load being tested. (A tradesmen is unlikely to
be carrying around a super expensive high-impedance laboratory analogue
meter, were as high impedance digital meters are common).
I have a recollection that at least one test manufacture makes DVMs that
have a lower than normal impedance (for a DVM) for exactly this sort of
use, ensuring circuits are well and truly dead before beginning work on
them.

Of course test lamps are a 'real load' and tell the story. But the test
lamps used by an electrician when working on 'domestic' mains won't last
very long if you tried to use them to see if the 3rd (or 4th) rail was
live. A bit too much juice!
Some one who regularly works on railway power systems may actually have
in their kit a 'test lamp' for 750v supplies.






--
Matthew Geier

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On Sun, 06 Apr 2008 18:18:36 +0100 (BST), "Dave Liquorice"
wrote:

On Sun, 06 Apr 2008 03:28:47 +0100, Charles Ellson wrote:

A meter can be misleading if it has a high impedance, as many modern
meters do. It'll measure voltages induced into the wire that are not
actually there if you apply even a small "load".

In that case it will still show _at least_ the possible voltage that
contact might be made with even if the available current is minimal.

Only a *possible* volts and volts only jolt, it's mills that kills.

You can't get the mils if the volts aren't pushing hard enough. As for
"possible" volts, see below.

As the source impedance is so high the moment you try to take any current
all the voltage is dropped across the source impedance leaving naff all
across the "load".

With some types of circuitry you can have a non-permanent defect
between the source and the point of measurement which gives a high
voltage reading but a low current. You only need the "blockage" to
clear or to have a suitable device capable of being charged up (a
capacitor being a simple example) then you might achieve sufficient
current flow for danger. The presence of unexplained excess voltage
should result in investigation or other safety measures.

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On Sun, 6 Apr 2008 21:18:22 +0100, Matthew Geier wrote

Some one who regularly works on railway power systems may actually have
in their kit a 'test lamp' for 750v supplies.

IIRC, it's a bank of lamps "just in case" one or two lamps have blown

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On Sun, 06 Apr 2008 23:06:05 +0100, Charles Ellson wrote:

With some types of circuitry you can have a non-permanent defect
between the source and the point of measurement which gives a high
voltage reading but a low current. You only need the "blockage" to
clear or to have a suitable device capable of being charged up (a
capacitor being a simple example) then you might achieve sufficient
current flow for danger. The presence of unexplained excess voltage
should result in investigation or other safety measures.

Hence the old acronym SIDE:

Switch off, Isolate, Dump, Earth

--
Cheers
Dave.

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On 7 Apr, 08:34, Stimpy wrote:
On Sun, 6 Apr 2008 21:18:22 +0100, Matthew Geier wrote



*Some one who regularly works on railway power systems may actually have
in their kit a 'test lamp' for 750v supplies.

IIRC, it's a bank of lamps "just in case" one or two lamps have blown

I'm sure I remember Peter Purves going into the Underground with a
maintenance team for Blue Peter in the 1970s, and being shown a bank
of twelve light bulbs "just in case".

(I also remember his reference to "the hiss of opening doors", despite
there being no such thing till the D78 stock [or since?]. In those
days the doors all opened silently and popped before closing.)