Crossing London tube tracks
spam_all...@yahoo.com
potential assailants positioned between oneself and the exit. In such
situations the only means of escape, should the group turn hostile,
would be across the tracks to the neighbouring platform.
What is the recommended method of crossing tracks in these situations?
There seem to be a variable number of rails making up the tracks,
usually about 5. Which of these are 'live'?
Will stepping on a live rail result in immediate death? What is the
safe distance from a live rail? Is it safe to tread on a live rail
with only one foot with the other in the air, in order to avoid
earthing the current?
Graeme Wall
spam_all...@yahoo.com wrote:
> It is very easy to find oneself on a tube platform with a group of
> potential assailants positioned between oneself and the exit. In such
> situations the only means of escape, should the group turn hostile,
> would be across the tracks to the neighbouring platform.
>
> What is the recommended method of crossing tracks in these situations?
Don't.
>
> There seem to be a variable number of rails making up the tracks,
> usually about 5. Which of these are 'live'?
There are 4 rails, all carry electrical currents at different potentials.
>
> Will stepping on a live rail result in immediate death?
Not unlikely
> What is the safe distance from a live rail?
The platform.
> Is it safe to tread on a live rail with only one foot with the other in
> the air, in order to avoid earthing the current?
No.
--
Graeme Wall
This address is not read, substitute trains for rail.
Transport Miscellany at <http://www.greywall.demon.co.uk/rail/index.html>
Charles Ellson
spam_all...@yahoo.com
> > What is the recommended method of crossing tracks in these situations?
>
> Don't.
So, your recommendation would be to remain on the platform and be
assaulted? I'm sure the death-rate for crossing tracks is not
negligible, but surely it is not as high as the death-rate from being
stabbed in the chest?
> > There seem to be a variable number of rails making up the tracks,
> > usually about 5. Which of these are 'live'?
>
> There are 4 rails, all carry electrical currents at different potentials.
So just avoid all of them then? Thanks for the info. Could be
especially useful if the assailants attempt to give chase and are
unaware of what will happen to them if they tread on the rails.
> > What is the safe distance from a live rail?
>
> The platform.
I live near a tube track and have, over the years, seen thousands of
workmen cross the tracks (as well as a few drunk teenagers). They all
survived, so your statement that it is impossible to get near a track
safely is untrue.
Graeme Wall
spam_all...@yahoo.com wrote:
> On 27 Mar, 18:09, Graeme Wall <R...@greywall.demon.co.uk> wrote:
>
> > > What is the recommended method of crossing tracks in these situations?
> >
> > Don't.
>
> So, your recommendation would be to remain on the platform and be
> assaulted? I'm sure the death-rate for crossing tracks is not
> negligible, but surely it is not as high as the death-rate from being
> stabbed in the chest?
How many people have been electrocuted by live rails and how many have been
stabbed on Underground stations?
>
> > > There seem to be a variable number of rails making up the tracks,
> > > usually about 5. Which of these are 'live'?
> >
> > There are 4 rails, all carry electrical currents at different potentials.
>
> So just avoid all of them then? Thanks for the info. Could be
> especially useful if the assailants attempt to give chase and are
> unaware of what will happen to them if they tread on the rails.
How many people have been chased by potential assailants on Underground
stations?
>
> > > What is the safe distance from a live rail?
> >
> > The platform.
>
> I live near a tube track and have, over the years, seen thousands of
> workmen cross the tracks (as well as a few drunk teenagers). They all
> survived, so your statement that it is impossible to get near a track
> safely is untrue.
>
I ddn't say it was impossible, I said the safe distance was from the
platform. The workmen are trained to cross the tracks safely and the power
is often switched off when they cross anyway.
Jane Sullivan
<6d17d8be-21f6-47bf...@59g2000hsb.googlegroups.com>,
spam_all...@yahoo.com writes
>It is very easy to find oneself on a tube platform with a group of
>potential assailants positioned between oneself and the exit. In such
>situations the only means of escape, should the group turn hostile,
>would be across the tracks to the neighbouring platform.
As I understand it you cannot cross the rails to another platform on the
tube except where the stations are in the open air. On the sub-surface
lines (i.e. not the tube), you can, though.
>
>What is the recommended method of crossing tracks in these situations?
By the footbridge, subway or equivalent.
>
>There seem to be a variable number of rails making up the tracks,
>usually about 5. Which of these are 'live'?
You should assume that all of them are live.
>
>Will stepping on a live rail result in immediate death?
It might and it might not. It depends what is insulating your feet.
However, you don't have to step on a rail to contact it: you could brush
against it or, if the voltage is high enough and you get close enough to
the rail without touching it, you could get a flashover.
Note that stepping on a live rail doesn't seem to affect the pigeons.
> What is the
>safe distance from a live rail?
Stay on the platform. It is against the law for an unauthorised person
to be on the track.
> Is it safe to tread on a live rail
>with only one foot with the other in the air, in order to avoid
>earthing the current?
--
Jane
British OO, American and Australian HO, and DCC in the garden
http://www.yddraiggoch.demon.co.uk/railway/railway.html
Charles Ellson
wrote:
Not getting killed by something does not mean that it was "safe".
Adrian
A Mr. Charles Bronson gave many demonstrations on how to handle such
situations. I cite his excellent series of movies titled "Death Wish
_"
Adrian
Bill Ridgeway
news:6d17d8be-21f6-47bf...@59g2000hsb.googlegroups.com...
Others have already commented that it would be better to stay on the
platform. Crossing live rails and stabbing are both potentially lethal and
both potentially survivable. The Ambulance Service can quickly get to a
stab victim on a platform. In contrast, a casualty electrocuted on the
juice entails stopping services both ways before the Fire Service and
Ambulance Service can get to them wasting what could be valuable time. Of
course if the casualty has also been hit by a train the whole thing gets
rather more messy and survivability is dramatically decreased. It would
seem that, on balance of probability, staying on the platform is a better
prospect than crossing live rails.
Bill
Gavin Christie
It's definitely not advisable to try and cross the tracks at all. Bear in
mind that all tube stations are extensively covered by CCTV these days and
the chances of any assailants even making it out of the station without
being arrested are small.
If you really do find yourself in the highly unlikely situation of being
menaced by a clockwork orange gang and you dont have a sock full of billiard
balls handy, the running rails typically have no current going through them.
The rail in the middle and the outside 4th rail are the ones to watch out
for. they have -210 volts and +420 volts running through them respectively.
In the old days they did use the running rails as earth/return current rails
but as far as I know they dont these days due to problems with arcing and
current spilling off into tunnel linings and gas and water mains.
Very, very foolish to even think about running across the tracks though.
You'd probably be in as much trouble as if you were the assailant maybe even
more so.
G
<spam_all...@yahoo.com> wrote in message
news:6d17d8be-21f6-47bf...@59g2000hsb.googlegroups.com...
Chris Tolley
> It is very easy to find oneself on a tube platform with a group of
> potential assailants positioned between oneself and the exit.
Perhaps if you trolled less, you'd have fewer potential assailants.
--
http://gallery120232.fotopic.net/p13309777.html
(47 365 at Tyseley, 1986)
Mizter T
> spam_all_you_w...@yahoo.com wrote:
> > It is very easy to find oneself on a tube platform with a group of
> > potential assailants positioned between oneself and the exit.
>
Quite. It must be tiresome being such a tit.
Owain
> Will stepping on a live rail result in immediate death?
If you're lucky.
The alternatives could be rather horrible.
Owain
Owain
> Others have already commented that it would be better to stay on the
> platform. Crossing live rails and stabbing are both potentially lethal and
> both potentially survivable. The Ambulance Service can quickly get to a
> stab victim on a platform. In contrast, a casualty electrocuted on the
> juice entails stopping services both ways before the Fire Service and
> Ambulance Service can get to them wasting what could be valuable time.
This I think is a Very Good Point.
Owain
D7666
wrote:
> As I understand it you cannot cross the rails to another platform on the
> tube except where the stations are in the open air. On the sub-surface
> lines (i.e. not the tube), you can, though.
Even that is not true.
There are many open sections where that are ''line clear'' (which
means in simple terms are treated the same as tunnels) i.e. the
Jubilee all the between Stratford and Canning Town portal is one.
--
Nick
Mr Thant
> There are many open sections where that are ''line clear'' (which
> means in simple terms are treated the same as tunnels) i.e. the
> Jubilee all the between Stratford and Canning Town portal is one.
I think we can all wholeheartedly recommend jumping between the
platforms on that stretch (well, except the third one at Stratford).
U
--
http://londonconnections.blogspot.com/
A blog about transport projects in London
Brownz (Mobile)
Trial & error, its the only way to know for sure.
I suggest you give it a go, trying each rail in turn.
Remember to wear the proper safety gear e.g. heavy cotton or woolen clothing
soaked in Water (or lighter fluid), and heavy wet woolen socks with no boots
or shoes.
If you don't detect a tingling sensation then you might want to lie on the
track and wait for the next train to come along, the driver will see you
laying there and he'll stop, you can then knock on the cab door and ask him.
Please feel free to report your findings back to the group.
(PS - Some or all of the above statements may well be false)
--
Cheerz - Brownz
'89 K100RS
'53 JCW MCS (Cage)
http://www.brownz.org/
Huss
(Mobile)" <someo...@microsoft.com> writes
(Laughing very loudly.)
I recommend the use of army ammunition boots, with metal plates fore and
aft. This gives the wearer a skating chance of making a meteoric
impression.
--
Huss
Why so large a cost, having so short a lease, does thou upon your fading
mansion spend?
William Shakespeare
Clive D. W. Feather
<gavc...@optonline.net> writes
>the running rails typically have no current going through them.
False, though it will be a relatively low current and voltage.
>The rail in the middle and the outside 4th rail are the ones to watch out
>for. they have -210 volts and +420 volts running through them respectively.
Approximately. They can be up to +750V in some places.
--
Clive D.W. Feather | Home: <cl...@davros.org>
Tel: +44 20 8495 6138 (work) | Web: <http://www.davros.org>
Fax: +44 870 051 9937 | Work: <cl...@demon.net>
Please reply to the Reply-To address, which is: <cl...@davros.org>
amo...@yahoo.com
you'd need at least 50kV for that under normal conditions.
There are, however, people who have survived much higher voltages, but
many have taken lasting damage in the process.
There are also people who have been killed by 50V.
It all depends on the duration of your exposure, the impedance of the
return path and the part(s) of your body the current flows through.
5 milliamps is sufficient to permanently stop your heartbeat. So you
could theoretically kill somebody with a watch battery. You'd have to
dig the electrodes into the heart tissue first though, so that sort of
thing is unlikely to happen by accident.
On the other hand, there are people whose hands or legs have been
roast to cinders, but who survived because the current didn't get
anywhere near any vital organs.
The safest advice is, never mess with electricity.
Roger T.
> There are, however, people who have survived much higher voltages, but
> many have taken lasting damage in the process.
Even the Americans can't electocute instantly, with 100% certainty, people
who have been sentanced to death by electric chair. That can be a slow,
painful death, requiring several attempts, before the subject dies.
--
Cheers
Roger T.
Home of the Great Eastern Railway at:-
http://www.highspeedplus.com/~rogertra/
Latitude: 48° 25' North
Longitude: 123° 21' West
Adrian
sounding much like they were saying:
>> There are, however, people who have survived much higher voltages, but
>> many have taken lasting damage in the process.
> Even the Americans can't electocute instantly, with 100% certainty,
> people who have been sentanced to death by electric chair. That can be a
> slow, painful death, requiring several attempts, before the subject
> dies.
Yebbut they only use 110v.
MIG
> Roger T. ("Roger T." <roger...@highspeedplus.com>) gurgled happily,
For safety, presumably?
Owain
>> Even the Americans can't electocute instantly, with 100% certainty,
>> people who have been sentanced to death by electric chair.
Don't they have 220V outlets for washing machines and electric chairs?
Owain
Roger T.
Driers are 240VAC, four pin outlets.
Washing machine 110-120VAC 'U' ground as are most every other outlets in
modern homes. Older homes, those built say mid to post 1950s, may still
have 2 pin, no ground outlets. Yes, the U.S.A. electrical code is not the
world's safest. Things that do down there are not permitted in Canada, which
also uses 120VAC.
Charles Ellson
<owain...@stirlingcity.coo.uk> wrote:
>Adrian wrote:
>>> Even the Americans can't electocute instantly, with 100% certainty,
>>> people who have been sentanced to death by electric chair.
>> Yebbut they only use 110v.
>
Up to around 3000v DC off a local generator IIRC (thus the dimming of
the prison lights as seen in many films is a load of old cobblers).
There was a DC v AC competition involving the public killing of an
elephant in the early days of deciding the "best" way to fry people;
prior to that Thomas Edison "perfected" his AC system by killing
numerous cats and dogs in experiments :-
http://www.ccadp.org/electricchair.htm
>Don't they have 220V outlets for washing machines
>
Two opposite phases on a 110-0-110 (180deg) supply IIRC except for one
state (Vermont?) which has (or had ?) "real" 240v in some or all of
it.
>and electric chairs?
Jules
120V/60Hz here for mains, 240V/60Hz for the bigger stuff (washing machine,
dryer, fridge and cooker in our case). Can't comment on the electric chair :-)
cheers
Jules
Owain
> Yes, the U.S.A. electrical code is not the
> world's safest.
Some of the stuff on electrical-contractor.net is *frightening*
Owain
Bruce Fletcher (Stronsay, Orkney)
> Up to around 3000v DC off a local generator IIRC (thus the dimming of
> the prison lights as seen in many films is a load of old cobblers).
> There was a DC v AC competition involving the public killing of an
> elephant in the early days of deciding the "best" way to fry people;
> prior to that Thomas Edison "perfected" his AC system by killing
> numerous cats and dogs in experiments
Was it not Edison who was so convinced that DC was the only way to
proceed and tried his best to show that Tesla and his AC system was a
mistake?
Bruce
Charles Ellson
Yes, that was the reason the elephant had to die, although it looks
like as you say that it was DC that Edison espoused but AC that the
unfortunate "Topsy" was cooked with to prove that she would have been
safer (but equally dead) with a unidirectional jolt :-
http://www.boingboing.net/2008/01/03/edison-electrocuted.html
Although apparently "she had to die" anyway (Topsy 3 Keepers 0) :-
http://www.roadsideamerica.com/pet/topsy.html
but carrots laced with cyanide merely made a tasty treat and there
wasn't a big enough gallows. Surprisingly, no-one seems to have
considered having her shot.
Roger T.
> the prison lights as seen in many films is a load of old cobblers).
> There was a DC v AC competition involving the public killing of an
> elephant in the early days of deciding the "best" way to fry people;
> prior to that Thomas Edison "perfected" his AC system by killing
> numerous cats and dogs in experiments :-
> http://www.ccadp.org/electricchair.htm
The local SPCA used to electrocute animals. Then they went to gassing, now
it's the needle.
MaxB
> > Up to around 3000v DC off a local generator IIRC (thus the dimming of
> > the prison lights as seen in many films is a load of old cobblers).
> > There was a DC v AC competition involving the public killing of an
> > elephant in the early days of deciding the "best" way to fry people;
> > prior to that Thomas Edison "perfected" his AC system by killing
> > numerous cats and dogs in experiments :-
> >http://www.ccadp.org/electricchair.htm
>
> The local SPCA used to electrocute animals. Then they went to gassing, now
> it's the needle.
>
> --
> Cheers
>
> Roger T.
> Latitude: 48° 25' North
> Longitude: 123° 21' West
When we lived next to a 750v 3rd rail line, in the days when you could
have an allotment on the bank, our cat used to wander on to the tracks
quite regularly until one day, we assume, his tail swished against the
rail. When we finally caught up with him, there was a horrible smell
of singed fur and a bald patch on his tail. He kept away from the
rails after that.
I always understood that AC killed by high voltages but threw you off
so you might survive, but DC killed with low voltages because you just
stuck there!
MaxB
Bill Again
>From: "MaxB" <batm...@bigfoot.com>
>Subject: Re: Crossing London tube tracks
>Date: 03 April 2008 08:52
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.
Stimpy
>
> 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!
John Rowland
>
> Even the Americans can't electocute instantly, with 100% certainty,
> people who have been sentanced to death by electric chair. That can
> be a slow, painful death, requiring several attempts, before the
> subject dies.
I thought you couldn't be charged twice for the one crime?
Peter Masson
"John Rowland" <jo...@journeyflow.spamspam.demon.co.uk> wrote in message
news:ft2lh2$guu$1$8300...@news.demon.co.uk...
acquittal, if new evidence is discovered which could not have been available
at the original trial.
Peter
James Farrar
*groan*
BH Williams
"James Farrar" <james.s...@gmail.com> wrote in message
news:inv9v39tigicmubcv...@4ax.com...
Someone had to say it.....
Brian
Stimpy
>
>>> I thought you couldn't be charged twice for the one crime?
>>
>> *groan*
> 'Shocking'
> Someone had to say it.....
I know someone who got arrested for being in possession of a stolen battery
and some fireworks...
They charged him then let him off :-)
Adrian
In the UK that is the case. Not so in most of these US. Although I
belive Louisianna comes close to allowing retrials.
Adrian
Roger T.
> > > people who have been sentanced to death by electric chair. That can
> > > be a slow, painful death, requiring several attempts, before the
> > > subject dies.
>
> > I thought you couldn't be charged twice for the one crime?
>
> There are now circumstances under which you can be tried again, following
> an
> acquittal, if new evidence is discovered which could not have been
> available
> at the original trial.
>
> Peter
In the UK that is the case. Not so in most of these US. Although I
belive Louisianna comes close to allowing retrials.
--------------------------------------
I think you both missed his humour. Being "charged" (As in electrical
charge) twice for the same crime.
Charles Ellson
wrote:
>On 3 Apr, 06:02, "Roger T." <roger...@highspeedplus.com> wrote:
>> > Up to around 3000v DC off a local generator IIRC (thus the dimming of
>> > the prison lights as seen in many films is a load of old cobblers).
>> > There was a DC v AC competition involving the public killing of an
>> > elephant in the early days of deciding the "best" way to fry people;
>> > prior to that Thomas Edison "perfected" his AC system by killing
>> > numerous cats and dogs in experiments :-
>> >http://www.ccadp.org/electricchair.htm
>>
>> The local SPCA used to electrocute animals. Then they went to gassing, now
>> it's the needle.
>>
>When we lived next to a 750v 3rd rail line, in the days when you could
>have an allotment on the bank, our cat used to wander on to the tracks
>quite regularly until one day, we assume, his tail swished against the
>rail. When we finally caught up with him, there was a horrible smell
>of singed fur and a bald patch on his tail. He kept away from the
>rails after that.
>
>I always understood that AC killed by high voltages but threw you off
>so you might survive, but DC killed with low voltages because you just
>stuck there!
>
There's a lot of pub science involved. Whether you get thrown away or
hang on more likely depends on which muscles are affected and/or
whether being thrown away is actually the result of a reflex reaction
to a shock that might not actually be life-threatening. Either are
equally harmful from the POV of burns (which can be internal and
follow bones) caused by the passage of enough current through the body
distinct from any effect upon the heart's rhythm.
Charles Ellson
<adrian_...@yahoo.com> wrote:
>On Apr 3, 7:07 am, "Peter Masson" <peter.mass...@privacy.net> wrote:
>> "John Rowland" <jo...@journeyflow.spamspam.demon.co.uk> wrote in message
>>
>> news:ft2lh2$guu$1$8300...@news.demon.co.uk...> Roger T. wrote:
>>
>> > > Even the Americans can't electocute instantly, with 100% certainty,
>> > > people who have been sentanced to death by electric chair. That can
>> > > be a slow, painful death, requiring several attempts, before the
>> > > subject dies.
>>
>> > I thought you couldn't be charged twice for the one crime?
>>
>> There are now circumstances under which you can be tried again, following an
>> acquittal, if new evidence is discovered which could not have been available
>> at the original trial.
>
>In the UK that is the case.
>
Not the UK, just England and Wales. The existing rules against "double
jeopardy" still apply in Scotland and (AFAICT) Northern Ireland.
Dave Liquorice
> 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.
--
Cheers
Dave.
Adrian
As is so often the case, common sense, a sense of history, and good
justice prevail in Scotland.
Mizter T
On 3 Apr, 22:58, Adrian <adrian_h_hud...@yahoo.com> wrote:
> On Apr 3, 1:09 pm, Charles Ellson <char...@ellson.demon.co.uk> wrote:
>
> > Not the UK, just England and Wales. The existing rules against "double
> > jeopardy" still apply in Scotland and (AFAICT) Northern Ireland.
>
>
> As is so often the case, common sense, a sense of history, and good
> justice prevail in Scotland.
That, and an extreme aversion to sobriety.
Adrian
:-) Aye, that too!
Bruce Fletcher (Stronsay, Orkney)
> Hence the advise....
>
> 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!
Bill
Liquorice <allsortsn...@howhill.com> writes
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
Dave Liquorice
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.
Charles Ellson
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.
Dave Liquorice
>> 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.
Matthew Geier
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
Charles Ellson
<allsortsn...@howhill.com> 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.
Stimpy
>
> 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
Dave Liquorice
> 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.
MIG
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.)
Andy Burns
> 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".
yes I remember that too, presumably 4 parallel sets of 3 lamps in series
so the -240/+410 gives each lamp about 250V?
keva...@holdthefrontpage.co.uk
Current Rail Indicator Devices. Fixed CRIDs are now being installed
on the headwall of many tube stations (small box with lights
indicating 'On', 'Off', 'Failed').
Andy Burns
> Current Rail Indicator Devices. Fixed CRIDs are now being installed
> on the headwall of many tube stations (small box with lights
> indicating 'On', 'Off', 'Failed').
thanks, that led me to this
http://www.tubelines.com/news/releases/200710/20071008.aspx
Charles Ellson
They all hiss when the seals are worn (and the door motors aren't
electric).
MIG
As I remember, in the 1938 to 1972 generations (that I was familiar
with), the doors would open silently (apart from the rumble of
movement). But they would pop before closing. The pop before closing
might be accompanied by a hiss if they were worn, and it was pretty
much as useful as bleepers for the punters, if unintentionally.
The 1973 and C77 stock made very little noise when opening or closing
(although I think there was still a delay before closing when the pop
would have been).
The D78 stock was very different (as mentioned in another reply), in
that it hissed loudly and continuously during both opening and
closing.
The modern stock makes very little air-related noise at all.
Anyway, whoever did the write-up for Blue Peter at the time obviously
never travelled on the Underground and was trying to be poetic.
tony sayer
<usenet.a...@adslpipe.co.uk> scribeth thus
I thought an 'eff off size shorting bar was the best insurance;!...
--
Tony Sayer
Charles Ellson
wrote:
It doesn't work if one conductor rail is isolated from the source.
Come to think of it, neither will the lamp which really needs to have
a third connection to 0v to do the job properly.
tony sayer
<cha...@ellson.demon.co.uk> scribeth thus
Well one would short pos and neg to the running rail//s..
--
Tony Sayer
Charles Ellson
wrote:
>In article <ki2nv3due2mkmpbk1...@4ax.com>, Charles Ellson
><cha...@ellson.demon.co.uk> scribeth thus
>>On Tue, 8 Apr 2008 09:52:47 +0100, tony sayer <to...@bancom.co.uk>
>>wrote:
>>
>>>In article <M8OdnaePt_78GmfanZ2dnUVZ8sTinZ2d@plusnet>, Andy Burns
>>><usenet.a...@adslpipe.co.uk> scribeth thus
>>>>On 07/04/2008 10:32, MIG wrote:
>>>>
>>>>> 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".
>>>>
>>>>yes I remember that too, presumably 4 parallel sets of 3 lamps in series
>>>>so the -240/+410 gives each lamp about 250V?
>>>
>>>I thought an 'eff off size shorting bar was the best insurance;!...
>>>
>>It doesn't work if one conductor rail is isolated from the source.
>>Come to think of it, neither will the lamp which really needs to have
>>a third connection to 0v to do the job properly.
>
>
>Well one would short pos and neg to the running rail//s..
>
That would be nearly the same as earthing of all phases on overhead
lines (seven clamps/clips and a spider of cable) but not quite. The
"box of eggs" is OK as long as someone looking at it realises that if
someone working further down the track has left off (or chopped) the
feed from one pole then the other could still be live if the supply
was switched on. It seems more of a warning that trains could approach
than of electrical safety; the FO short-circuit bar will stop the
trains (other than diesel/battery/etc.) but the usual rule about
treating anything as live unless it is obviously earthed seems to be
the main defence.
Matthew Geier
>>yes I remember that too, presumably 4 parallel sets of 3 lamps in series
>>so the -240/+410 gives each lamp about 250V?
>
> I thought an 'eff off size shorting bar was the best insurance;!...
You don't drop a shorting bar across a live supply. The effect would be
some what spectacular and will probably throw molten metal around,
possibly causing nasty injuries.
People have been injured in the power industry by closing earthing
switches onto a live supply and then being splattered with molten metal
when the earth switch vaporised. (As they are not designed to switch live
and take the full fault current across their closing contacts)
You don't short the circuit till you have tested it's actually dead.
Then short it so that if some one accidentally turns it back on while you
are working on it, the short circuit causes it to trip off again. And you
make short your short is securely attached so that in the event is really
does get energised, the sudden large current flow doesn't cause the
shorting wire/bar to fly off and disconnect itself, thus allowing the
circuit to be fully energized and then fry you.
--
Matthew Geier
Matthew Geier
> but the usual rule about treating anything as
> live unless it is obviously earthed seems to be the main defence.
As a friend who worked in the power industry once said - 'The only thing
I trust is a metre air gap'.
Any one working on a high power system will want the assurance some
idiot can't turn it back on and kill them, hence the highly visible short
to earth bars/wires. If some one tries to turn it back on, the short to
earth should be a sufficiently good 'fault' to trip it off again saving
your own skin from such stupidity.
An people do try to turn things back on again. I've seen at least one
report were a circuit was isolated for work, and a remote control centre
forgot about the work, saw the isolated circuit as a fault and tried to
remotely turn the power on again...
The earthing cables saved the guys out on site.
--
Matthew Geier
tony sayer
Geier <mat...@wibble-blah.sleeper.apana.org.au> scribeth thus
Ever heard of SIDE?.
Switch off
Isolate
Dump
Earth
One wouldn't recommend for a moment chucking an earthing bar or cables
across a live line!.
A shorting/earthing system should be suitable for the currents involved.
There will be a difference for linesmen working on an 11 kV overhead to
someone on an LU line!...
--
Tony Sayer
David Hansen
<mat...@wibble-blah.sleeper.apana.org.au> wrote this:-
> Any one working on a high power system will want the assurance some
>idiot can't turn it back on and kill them, hence the highly visible short
>to earth bars/wires. If some one tries to turn it back on, the short to
>earth should be a sufficiently good 'fault' to trip it off again saving
>your own skin from such stupidity.
That rather depends on the system. For example it is difficult to
apply an earthing wire to a cable one is about to open up to joint,
but one is a sensible precaution on a bare conductor.
Where the system covers a relatively small area then the obvious way
to manage things is to use locks. If people are doing the same sort
of work over a small area then they can have their own lock which
they keep the key to. An example would be a workshop where several
people work on the electrical parts of a train.
If there is a larger system with someone responsible for the whole
system then the way to manage it is to use locks, the keys for which
are locked into a box. This box has a key for those doing the work
and a key for the person responsible for the system.
Such systems become unmanageable over large areas with remotely
operated switchgear.
--
David Hansen, Edinburgh
I will *always* explain revoked encryption keys, unless RIP prevents me
http://www.opsi.gov.uk/acts/acts2000/00023--e.htm#54
funkmish
Four regular 40w lamps wired in parallel should do the trick. The problem comes
when one of them blows :)
Andy Burns
> Four regular 40w lamps wired in parallel should do the trick. The
> problem comes when one of them blows :)
Four 240V lamps wired in parallel across a 750V supply would blow rather
quickly I'd expect. You should try to explain that you meant to say "in
series" at this point ;-)
funkmish
Yes, I meant in series, hence my comment about when one of them blows! No idea
why I typed parallel!!!
funkmish
Dr J R Stockton
Apr 2008 14:10:17, funkmish <funk...@address.invalid> posted:
When one blows, the full voltage will appear across it and its socket;
that is undoubtedly more that their designers expected them to receive,
and may be more than they can reliably stand, especially in an
environment which may be damp or mucky.
I am reminded that I once inherited an equipment which included a 3 kV
DC supply charging a cubic metre or so of capacitors via a couple of
dozen ordinary 200 V bulbs in series and an ordinary 1.25" cartridge
fuse and holder. One day, the fuse blew. The current continued, only
slightly impeded, until the burning fuse holder disintegrated.
--
(c) John Stockton, nr London UK. *@merlyn.demon.co.uk/??.Stockton@physics.org
Web <URL:http://www.merlyn.demon.co.uk/> - FAQish topics, acronyms, & links.
Correct <= 4-line sig. separator as above, a line precisely "-- " (SoRFC1036)
Do not Mail News to me. Before a reply, quote with ">" or "> " (SoRFC1036)
David Hansen
Stockton <j...@merlyn.demon.co.uk> wrote this:-
>an ordinary 1.25" cartridge fuse
What's one of those?
charles
David Hansen <SENDdavi...@spidacom.co.uk> wrote:
> On Mon, 14 Apr 2008 23:07:44 +0100 someone who may be Dr J R
> Stockton <j...@merlyn.demon.co.uk> wrote this:-
> >an ordinary 1.25" cartridge fuse
> What's one of those?
CPC part number: FS01458 etc.
--
From KT24 - in "Leafy Surrey"
Using a RISC OS computer running v5.11
David Hansen
<cha...@charleshope.demon.co.uk> wrote this:-
>> >an ordinary 1.25" cartridge fuse
>
>> What's one of those?
>
>CPC part number: FS01458 etc.
http://cpc.farnell.com says there is no such part.
To be of any use to people the OP should have given some useful
information, such as the current rating and (perhaps) the breaking
capacity of the fuse. The physical sizes of fuses are not useful.
If the intention was to be a little more coy then whether the
dimension quoted was the length or diameter would have been useful.
Andy Burns
> The physical sizes of fuses are not useful.
Sounds like it /would/ have been useful to choose a physically larger
fuse and holder on this occasion.
David Hansen
<usenet.a...@adslpipe.co.uk> wrote this:-
>> The physical sizes of fuses are not useful.
>
>Sounds like it /would/ have been useful to choose a physically larger
>fuse and holder on this occasion.
Quite likely. However, only some ranges of fuses have different
physical sizes for different electrical "sizes".
Clive
"David Hansen" <SENDdavi...@spidacom.co.uk> wrote in message
news:hdq804h5r8kia0p6k...@4ax.com...
> On Tue, 15 Apr 2008 08:55:31 +0100 someone who may be charles
> <cha...@charleshope.demon.co.uk> wrote this:-
>
> >> >an ordinary 1.25" cartridge fuse
> >
> >> What's one of those?
> >
> >CPC part number: FS01458 etc.
>
> http://cpc.farnell.com says there is no such part.
>
> To be of any use to people the OP should have given some useful
> information, such as the current rating and (perhaps) the breaking
> capacity of the fuse. The physical sizes of fuses are not useful.
>
> If the intention was to be a little more coy then whether the
> dimension quoted was the length or diameter would have been useful.
>
The physical size of the fuse IS important when you are considering
spark-gaps etc, which is what caused the dramatic failure in this case.
"1.25" cartridge fuse" is a well known specification, I use them daily.
MB
from David Hansen <SENDdavi...@spidacom.co.uk> contains these words:
> On Tue, 15 Apr 2008 08:55:31 +0100 someone who may be charles
> <cha...@charleshope.demon.co.uk> wrote this:-
> >> >an ordinary 1.25" cartridge fuse
> >
> >> What's one of those?
> >
> >CPC part number: FS01458 etc.
> http://cpc.farnell.com says there is no such part.
> To be of any use to people the OP should have given some useful
> information, such as the current rating and (perhaps) the breaking
> capacity of the fuse. The physical sizes of fuses are not useful.
> If the intention was to be a little more coy then whether the
> dimension quoted was the length or diameter would have been useful.
It seemed a perfectly acceptable description to me. From what I
remember there are basically three common types of cartridge fuses 5/8",
1 1/4" and 20MM which have been in common use for many years so should
be recognisable to anyone with any knowledge of electronics. I think
they have a BS number beginning 29 i.e. BS29xx but can't find a
catalogue at the moment.
MB
David Hansen
<cas...@bigfoot.com> wrote this:-
>The physical size of the fuse IS important when you are considering
>spark-gaps etc, which is what caused the dramatic failure in this case.
Incorrect. What is important in this respect is the breaking
capacity of the fuse. Different designs of fuse, with the same
physical dimensions, are able to reliably break different currents.
The same is true of different designs of miniature circuit breaker.
Clive
> On Tue, 15 Apr 2008 11:16:45 +0200 someone who may be "Clive"
> <cas...@bigfoot.com> wrote this:-
>
> >The physical size of the fuse IS important when you are considering
> >spark-gaps etc, which is what caused the dramatic failure in this case.
>
> Incorrect. What is important in this respect is the breaking
> capacity of the fuse. Different designs of fuse, with the same
> physical dimensions, are able to reliably break different currents.
> The same is true of different designs of miniature circuit breaker.
>
Depending on the voltage and not the current !
From the OP's description, the voltage was high enough so that when the fuse
blew, the air gap was insufficient to stop a spark forming, hence ionizing
the air in what had been the fuse housing causing the fuse holder to
disintegrate. In this case, it seems that the fuse was physically (and not
electrically) too small to stop this happening, regardless of the current.
//Clive.
David Hansen
<cas...@bigfoot.com> wrote this:-
>Depending on the voltage and not the current !
Any fuse holder will have a rated maximum voltage.
Clive
>
> Any fuse holder will have a rated maximum voltage.
>
So now you know what caused the OP's failure....
David Hansen
<cas...@bigfoot.com> wrote this:-
>So now you know what caused the OP's failure....
Nice try.
charles
David Hansen <SENDdavi...@spidacom.co.uk> wrote:
> On Tue, 15 Apr 2008 08:55:31 +0100 someone who may be charles
> <cha...@charleshope.demon.co.uk> wrote this:-
> >> >an ordinary 1.25" cartridge fuse
> >
> >> What's one of those?
> >
> >CPC part number: FS01458 etc.
> http://cpc.farnell.com says there is no such part.
sorry, it is FF01458.
> To be of any use to people the OP should have given some useful
> information, such as the current rating and (perhaps) the breaking
> capacity of the fuse. The physical sizes of fuses are not useful.
> If the intention was to be a little more coy then whether the
> dimension quoted was the length or diameter would have been useful.
--
Jules
>> If the intention was to be a little more coy then whether the
>> dimension quoted was the length or diameter would have been useful.
>
> It seemed a perfectly acceptable description to me. From what I
> remember there are basically three common types of cartridge fuses 5/8",
> 1 1/4" and 20MM which have been in common use for many years so should
> be recognisable to anyone with any knowledge of electronics.
Although don't discount the bigger ones of around 3" length and 3/4"
diameter, commonly used as primary fuses for heavier currents - I bet
there's quite a few still kicking around in old houses, big old power
control equipment etc.
cheers
Jules
David Hansen
<cha...@charleshope.demon.co.uk> wrote this:-
>> http://cpc.farnell.com says there is no such part.
>
>sorry, it is FF01458.
Thanks.
Voltage rating, AC:250V
Current, fuse rating:10A
Current, breaking capacity AC:200A
If I had inherited equipment which included a 3 kV DC supply
charging a cubic metre or so of capacitors via a couple of dozen
ordinary 200 V bulbs in series then I would have thought about such
a fuse and then replaced it with something suitable.
We don't know precisely what caused the fuse to operate, but we do
know that the fuse was unable to break the current which was flowing
at the time.
Jeff
">
>>The physical size of the fuse IS important when you are considering
>>spark-gaps etc, which is what caused the dramatic failure in this case.
>
> Incorrect. What is important in this respect is the breaking
> capacity of the fuse. Different designs of fuse, with the same
> physical dimensions, are able to reliably break different currents.
Not incorrect, some fuses have fillers in the tube to help prevent arcing at
EHT voltages. Fuses will normally have a voltage rating as well as a current
rating and type (fast blow, anti surge etc.)
Jeff
Bill Again
"Jeff" <je...@local.host> wrote in message
news:4804e39e$0$6430$834e...@reader.greatnowhere.com...
Even these little household fuses are filled with sand to do exactly that
job.
David Hansen
<je...@local.host> wrote this:-
>>>The physical size of the fuse IS important when you are considering
>>>spark-gaps etc, which is what caused the dramatic failure in this case.
>>
>> Incorrect. What is important in this respect is the breaking
>> capacity of the fuse. Different designs of fuse, with the same
>> physical dimensions, are able to reliably break different currents.
>
>
>Not incorrect, some fuses have fillers in the tube to help prevent arcing at
>EHT voltages.
Incorrect. The "fillers" (and indeed the nature of the fuse element)
are one of the determinants of the breaking capacity.
EHT is not a term which is defined in the usual sources. Perhaps you
could tell us what your definition is?
>Fuses will normally have a voltage rating as well as a current
>rating and type (fast blow, anti surge etc.)
The voltage was stated in the CPC information I was eventually able
to quote. Readers may have noted that none of the information was
for DC.
Clive
> On Tue, 15 Apr 2008 18:18:08 +0100 someone who may be "Jeff"
> <je...@local.host> wrote this:-
>
> >>>The physical size of the fuse IS important when you are considering
> >>>spark-gaps etc, which is what caused the dramatic failure in this case.
> >>
> >> Incorrect. What is important in this respect is the breaking
> >> capacity of the fuse. Different designs of fuse, with the same
> >> physical dimensions, are able to reliably break different currents.
> >
> >
> >Not incorrect, some fuses have fillers in the tube to help prevent arcing
at
> >EHT voltages.
>
> Incorrect. The "fillers" (and indeed the nature of the fuse element)
> are one of the determinants of the breaking capacity.
>
Incorrect, filling a fuse body with sand provides additional protection
against arcing in an overcurrent situation.
Jeff
"Clive" <cas...@bigfoot.com> wrote in message
news:fu47r0$p9j$1...@news.al.sw.ericsson.se...
Only partially incorrect; the filler will have an effect on the breaking
current of the wire due to added thermal capacity, but that is not its
primary purpose, which is to prevent arcing. (the wire is gauge and
composition is modified to compensate for the filler).
Jeff
David Hansen
<cas...@bigfoot.com> wrote this:-
>Incorrect, filling a fuse body with sand provides additional protection
>against arcing in an overcurrent situation.
Glad we got there in the end. The fuse failed to break the current.
The mechanism by which it failed to break the current was that an
arc formed, which is the way fuses which fail to break the current
fail.
We don't know why the fuse operated and failed to break the current.
It may just have expired through old age, or there may have been a
large current flowing for some reason. However, this does not change
the fact that the fuse failed to break the current. If it had broken
the current then there would have been no arc.
Circuit breakers can fail to break the current in the same way. They
can also fail to break the current because the contacts don't move
or don't move far enough.
Also, as I have said before, the fuse referred to on the web site
does not appear to be specified for DC use. It will be able to break
some current, but its capacity to break DC current is going to be
rather less then breaking AC.
Jeff
>>against arcing in an overcurrent situation.
>
> Glad we got there in the end. The fuse failed to break the current.
> The mechanism by which it failed to break the current was that an
> arc formed, which is the way fuses which fail to break the current
> fail.
>
> We don't know why the fuse operated and failed to break the current.
> It may just have expired through old age, or there may have been a
> large current flowing for some reason. However, this does not change
> the fact that the fuse failed to break the current. If it had broken
> the current then there would have been no arc.
>
> Circuit breakers can fail to break the current in the same way. They
> can also fail to break the current because the contacts don't move
> or don't move far enough.
>
That is why 'serious' circuit breakers have compressed air blown onto the
gap to suppress arcing.
Jeff
Clive
> On Wed, 16 Apr 2008 08:54:23 +0200 someone who may be "Clive"
> <cas...@bigfoot.com> wrote this:-
>
> >Incorrect, filling a fuse body with sand provides additional protection
> >against arcing in an overcurrent situation.
>
> Glad we got there in the end. The fuse failed to break the current.
> The mechanism by which it failed to break the current was that an
> arc formed, which is the way fuses which fail to break the current
> fail.
>
Finally !
Mike
They used to, most modern "serious" circuit breakers of a significant
size use Sulphur Hexafluoride, or as it is more often called, ozone
killer.
--