"The positive rail is 3 inches higher than the running rails, while the negative rail is 1.5 inches higher. The positive insulators are thus twice the height of the negative ones and therefore have about twice the earth leakage resistance, so the voltages are set with a proportional disparity between the positive and negative voltage levels. The positive rail is at a potential of 420 volts above earth and the negative rail at 210 volts below earth."
changed since my day then, when underground ran on SR three rail systems quite happily...and could use either centre or side rail
I was always told that the centre rail was at earth to keep the resistance down. SR trains run OK on underground lines (not in the tunnels, obvs, too tall) but e.g. at East Putney you would sometimes see an empty SR train switched from the Putney SR line that goes on to Windsor, onto the District line going south to Wimbledon, where it could rejoin SR lines.
It's the world's fastest game for two pairs of hands. :-)
One morning when taking the SR train to Waterloo, I suddenly noticed we were in a tunnel. We were on the District Line between Wimbledon & East Putney. we came through Wandsworth Town into Clapham Junction. Obviously some tunnels will take standard trains, but not the deep tube ones.
When I was in the cadets at school many years ago I leant on the front of an old military radio. It turned out the three pins I hadn't noticed were for a supply to a matching transmitter.
At mains.
Across the palm of my hand.
It hurt, but didn't throw me anywhere.
I haven't had another shock since. Perhaps I'm paranoid enough.
Andy
Interesting.
Bill
What about a third and fourth time?
Bill
I'm going to avoid Australia in case they're all like you.
Bill
It's enough of a jolt that you don't do it more than twice.
And I thought it was just me. At a similar age - maybe 10 - I decided to make an electric car. I knew motors had windings. That was all I knew. I wound a wire around the metal axle of a lego car, and attached both ends to a battery. Strangely, nothing happened.
OBVIOUSLY I needed more oomph. I opened up a plug. Observing that there were three terminals, I decided to splice the wire into all three to see what would happen. I then made the only good decision I made that day. Instead of plugging in to the switched on socket, I elected to switch it off, plug in, and THEN switch on. Just as well, it blew the thing off the wall and blew the fuse at the board. I saw a flash but avoided any shock, which was more than could be said for my parents.
I also remember that when the electrician came round to fix it, I ended up with a double in my room where I had previously had a single. So that was a win.
It was one of my jokes.
Bill
You have a misunderstanding somewhere. No either about it , Not now and not since they were electrified over a
100 years ago whatever your day was when you made a wrong assumption. Underground passenger trains *, have to be in contact with both side and centre rails to complete their circuit, there is no path built in via the axles and wheels with brush gear to by pass axle bearings so they don?t get damaged by high currents passing through them like 3rd rail ( and overhead equipped ) trains have. What happens on the shared sections is the outer rail voltage is raised to the full potential required , once 630 but often now the later 750 .the centre rail is simply bonded to the running rails and is at ground potential. The observant who used the shared sections around around Putney may have noticed at one time to save money the centre rail was sometimes mounted on wooden blocks rather than insulators. Special arrangement have to be in place where the two systems meet so a train doesn?t bridge both system so there are long gaps in the live rails on Putney Bridge and between Turnham Green and Gunnesbury. Photos of the Putney bridge ones and a drivers description on this link.We are getting away from DIY but the technically nosy may find a detailed description of how such systems in the UK were developed here.
GH
Hum... tricky one... each persons reaction is different. Electric shock (no matter what voltage) can cause a bad reaction. First Aid advice (via My current employers HS dept) is straight to A&E for a cardiograph.
AC
110V (55-0-55) ouch 240V (Domestic, can be nasty - A&E for anything above a minor touch advised but not forced to go) 415V (3 phase) = Dead. Anything greater than 415V = Dead.DC Charged capacitor above 50V hurts Microwave 5kV or more capacitor = very nasty, A&E strongly advised.
Other things much more relevant than the particular voltage you have touched:-
Where the shock tracks through you, i.e. if it's from one hand to the other across your chest it's much more likely to do damage than if it's just across your hand or along a limb.
How dry your skin is and thus how much resistance you present to the flow of electricity.
How good an earth the 'earthy' end of your shock is, if you're barefoot on a wet floor it's going to be much worse than if you have rubber soles on a dry floor.
In the case of shocks from capacitors the total stored energy is also very important. That is why defibrillators are calibrated in Joules.
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