The two emergency wires on the tunnel wall

[Deleted]

When I was a new Met police constable in the early 80s in London we were told by an instructor (not BT police, he was Met) that the two wires on the tunnel wall you could squeeze together in an emergency and by so doing cut off all track power. I knew about the loose driver's handset that could be connected to those 2 wires, while a train was in a tunnel, to make emergency phone calls for example. But the squeezing together of the 2 wires to short out the power always seemed unlikely to me, but I never got round to having it confirmed or refuted by an expert.

So here I am 33 years later, asking, is it true or not?

And if it is true, has anyone ever done it?

I was only ever present at one police incident on underground tracks, on the Piccadilly at South Kensington, in the early 90s, and the power had already been switched off, I assume by more conventional means.

[PiccNT]

Yes true. The wires have a current of between 5 and 10 volts that energise a relay at the substation. Rub them together and the relay is de-energised and a circuit breaker opens at each end of that section. This is one of many ways to discharge traction current.

[Deleted]

Feb 7, 2017 22:48:03 GMT @innercircle said:

When I was a new police constable in the early 80s in London we were told by an instructor (not BT police, he was Met) that the two wires on the tunnel wall you could squeeze together in an emergency and by so doing cut off all track power. I knew about the loose driver's handset that could be connected to those 2 wires, while a train was in a tunnel, to make emergency phone calls for example. But the squeezing together of the 2 wires to short out the power always seemed unlikely to me, but I never got round to having it confirmed or refuted by an expert.

So here I am 33 years later, asking, is it true or not?

And if it is true, has anyone ever done it?

I was only ever present at one police incident on underground tracks, on the Piccadilly at South Kensington, in the early 90s, and the power had already been switched off, I assume by more conventional means.
    

Funny that you should refer to more conventional means. Before the introduction of radio, this was the way of discharging traction current.

[whistlekiller2000]

This thread has withdrawn and slightly modified to remove some sensitive information prior to its return. You can find previous discussion about it on this thread from 2010: Tunnel Telephone

Also, whilst the thread was in temporary quarantine, PiccNT  was kind enough to provide us with this link as well: Tubeprune Site

[Deleted]

Thanks for that, I didn't think it through. Sorry.

[Deleted]

Feb 7, 2017 22:53:40 GMT PiccNT said:

Yes true. The wires have a current of between 5 and 10 volts that energise a relay at the substation. Rub them together and the relay is de-energised and a circuit breaker opens at each end of that section. This is one of many ways to discharge traction current.

Thanks.

[Deleted]

Feb 7, 2017 22:57:34 GMT tut said:

Feb 7, 2017 22:48:03 GMT @innercircle said:

When I was a new police constable in the early 80s in London we were told by an instructor (not BT police, he was Met) that the two wires on the tunnel wall you could squeeze together in an emergency and by so doing cut off all track power. I knew about the loose driver's handset that could be connected to those 2 wires, while a train was in a tunnel, to make emergency phone calls for example. But the squeezing together of the 2 wires to short out the power always seemed unlikely to me, but I never got round to having it confirmed or refuted by an expert.

So here I am 33 years later, asking, is it true or not?

And if it is true, has anyone ever done it?

I was only ever present at one police incident on underground tracks, on the Piccadilly at South Kensington, in the early 90s, and the power had already been switched off, I assume by more conventional means....at least, I didn't see any colleagues Met or BT police standing by the tunnel mouth squeezing wires together.  
    

Funny that you should refer to more conventional means. Before the introduction of radio, this was the way of discharging traction current.

Oh right, that's very interesting, I always assumed it was a last resort kind of thing in the event of failure of a switch somewhere.  

[Deleted]

Feb 8, 2017 0:01:38 GMT @innercircle said:

Feb 7, 2017 22:57:34 GMT tut said:

Funny that you should refer to more conventional means. Before the introduction of radio, this was the way of discharging traction current.

Oh right, that's very interesting, I always assumed it was a last resort kind of thing in the event of failure of a switch somewhere.  

Well it is now, there are much better methods now. But one thing I find very interesting is that originally (not any more of course) on the Hainault-Woodford section of the Central line, the first resort was to use the tunnel telephone lines in the Grange Hill tunnel.

Quoting from the supplement to the traffic circular:

(b) On the open sections of the Inner and Outer Rail between Hainault and Woodford junction current will be switched off in emergency either by the Driver or Guard or other person concerned proceeding to the tunnel and operating the tunnel telephone line for the road concerned in accordance with Rule 244, or if they are not near the tunnel, by acting in accordance with Rule 247, clause (b)

This was 1948 though, don't imagine that's still the procedure!

[Deleted]

I meant that even back in the 80s I thought that it was a last resort back then, as it seemed such a hands on primitive method, even by 80s standards.

[Chris M]

I suspect it ceased to be the preferred method as soon as reliable radio communications were available, which I think was before the 1980s. I suspect the reason it is retained even today is that it is such a simple method there is almost nothing that can possibly go wrong - and the things most likely to go wrong (the wires becoming detached from the tunnel wall) would fail safe. It can of course be used as a way to discharge traction current by someone working in the tunnel should it become energised before it should be for any reason,* even if they don't have a radio to hand.
*I'd be surprised if there were fewer than at least two things that have to go wrong with systems and procedures before such could happen though.

I have no idea how often it gets used these days, but I guess that it will be tested at some defined interval.

[MoreToJack]

The wires are still tested and maintained, but they haven't been used in anger in at least 15 or so years. They currently represent one of the largest points leading to loss of traction current through accidental tripping, be it from people hanging banana skins etc off them (Finchley Road southbound Met used to be a prime location...) or simply the damp tunnel environments.

Every now and then proposals appear to decommission and remove them, but as yet this hasn't followed through. Notably, though, Moorgate to King's Cross has a 'new version' of the wires, consisting of fixed telephones every so often along the side of the tunnel. The (apparently) work in a similar way to the Headwall Tunnel Telephones which are another - and more often used - method of discharging traction current.

But yes - with the advent of Connect Radio the quickest way to discharge current is often through the emergency number to the controller, who will then flick the relevant switch on their tunnel telephone panel. It's good to have multiple backups and options though for something so vital!

[aslefshrugged]

Drivers are still trained to "pinch and rub" the tunnel telephone wires and I believe there's still a handset in the emergency equipment cabinet in the cab of the train (I've not opened one up for such a long time) but our usual method of discharging current is to hit the "mayday" button on the Connect train radio.

You have to "rub" after you "pinch" the wires together to get all the gunk off.

[class411]

I remember, many, many, years ago, the a Ladybird book (not sure which one), where it stated that in the event of an emergency the driver had to bring the two wires together with his bare hands, making it sound as if it was something dangerous that you needed to be very brave to do.

[brigham]

In Glasgow, you had a brass stick, in a wooden sleeve with cut-aways, to bridge the wires. Otherwise, the principle was the same.

[tjw]

Feb 8, 2017 8:49:28 GMT class411 said:

I remember, many, many, years ago, the a Ladybird book (not sure which one), where it stated that in the event of an emergency the driver had to bring the two wires together with his bare hands, making it sound as if it was something dangerous that you needed to be very brave to do.

I too found this information in a children's book on the tube "Railways under London, Neurath, 1948" It has diagrams of the relays, and also shows the relays that trips to turn on the tunnel lighting.

I suspect that the dangerous tone was to discourage unauthorised use.

[Deleted]

Feb 8, 2017 1:22:41 GMT MoreToJack said:

The wires are still tested and maintained, but they haven't been used in anger in at least 15 or so years. They currently represent one of the largest points leading to loss of traction current through accidental tripping, be it from people hanging banana skins etc off them (Finchley Road southbound Met used to be a prime location...) or simply the damp tunnel environments.

Every now and then proposals appear to decommission and remove them, but as yet this hasn't followed through. Notably, though, Moorgate to King's Cross has a 'new version' of the wires, consisting of fixed telephones every so often along the side of the tunnel. The (apparently) work in a similar way to the Headwall Tunnel Telephones which are another - and more often used - method of discharging traction current.

Headwall tunnel telephones are connected to the TT wires, as are section ahead/section in rear plungers, so they all have the same ultimate effect in the relevant substation(s) whatever component is used. The tunnel telephones between KX and Moorgate are provided in lieu of exposed wires due to the proximity of 25kV overhead electrification on Network Rail (albeit gone now east of Farringdon). The Heathrow T4 loop also has these phones.

Feb 8, 2017 8:49:28 GMT class411 said:

I remember, many, many, years ago, the a Ladybird book (not sure which one), where it stated that in the event of an emergency the driver had to bring the two wires together with his bare hands, making it sound as if it was something dangerous that you needed to be very brave to do.

For those interested the process is demonstrated in this video at 6:35

[Deleted]

Feb 8, 2017 1:01:27 GMT Chris M said:

I suspect the reason it is retained even today is that it is such a simple method there is almost nothing that can possibly go wrong 

Foolproof in an emergency in other words for bumbling coppers and firefighters   I see what you did there  

[Deleted]

I saw some of the instruction films years ago as well. But even earlier than that, I used to think "won't I get a shock if I touch the two wires?"

[North End]

Feb 8, 2017 11:52:28 GMT @innercircle said:

I saw some of the instruction films years ago as well. But even earlier than that, I used to think "won't I get a shock if I touch the two wires?"

I know someone who got a belt off them. Not sure of the exact circumstances but I think the wires had broken and were lying over one of the current rails.

[Dstock7080]

There is a mild tingling sensation when they are used.

[trt]

Feb 8, 2017 12:41:29 GMT Dstock7080 said:

There is a mild tingling sensation when they are used.

That's just the visceral thrill of it.

[Deleted]

Feb 7, 2017 22:57:34 GMT tut said:

Funny that you should refer to more conventional means. Before the introduction of radio, this was the way of discharging traction current.

Does anyone know roughly when this method fell into disuse, i.e. when train radio came into widespread use on all lines?

[Deleted]

Feb 8, 2017 14:09:45 GMT @davidwailing said:

Feb 7, 2017 22:57:34 GMT tut said:

Funny that you should refer to more conventional means. Before the introduction of radio, this was the way of discharging traction current.

Does anyone know roughly when this method fell into disuse, i.e. when train radio came into widespread use on all lines?

It hasn't fallen into disuse. It is still one of several methods available (to staff) for getting traction current discharged in an emergency.

[Deleted]

The film is appropriately dated 1989 - was that something to do with the 1989 Electricity at Work Act, and the new 1989 style Short Circuiting Bar being launched in response to the new law being introduced??

[rincew1nd]

Just watching that clip, in the background there is (what I think is) compressor noise, which stops when the wires are first pinched. Is this co-incidence or does the power trip almost instantly? If the former why the need to pinch again, or is this good practice to ensure that there has been electrical connection?

[Deleted]

Feb 9, 2017 21:13:53 GMT rincew1nd said:

Just watching that clip, in the background there is (what I think is) compressor noise, which stops when the wires are first pinched. Is this co-incidence or does the power trip almost instantly? If the former why the need to pinch again, or is this good practice to ensure that there has been electrical connection?

It's the Motor Alternator, and it is not a co-incidence; traction current should switch off immediately that the two wires are brought into contact. The technique exhibited is actually not what is taught, and as I think was mentioned upthread (and by the narrator), drivers are told to pinch and rub the wires together. In any case, after doing so, contact must be made with the line controller because s/he is the only person that can give confirmation that traction current has actually been discharged.

[Deleted]

Feb 9, 2017 18:24:44 GMT @wr24 said:

Feb 8, 2017 14:09:45 GMT @davidwailing said:

Does anyone know roughly when this method fell into disuse, i.e. when train radio came into widespread use on all lines?

It hasn't fallen into disuse. It is still one of several methods available (to staff) for getting traction current discharged in an emergency.

Sorry, I will clarify the question. When did train radio come into widespread use, and therefore lead to this method becoming less commonly used?

[North End]

Feb 9, 2017 22:58:35 GMT @davidwailing said:

Feb 9, 2017 18:24:44 GMT @wr24 said:

It hasn't fallen into disuse. It is still one of several methods available (to staff) for getting traction current discharged in an emergency.

Sorry, I will clarify the question. When did train radio come into widespread use, and therefore lead to this method becoming less commonly used?

I'd say only from the introduction of the Connect system, which is rather more dependable than what came before. So roughly 2008-2009.

[philthetube]

Feb 7, 2017 22:48:03 GMT @innercircle said:

When I was a new Met police constable in the early 80s in London we were told by an instructor (not BT police, he was Met) that the two wires on the tunnel wall you could squeeze together in an emergency and by so doing cut off all track power. I knew about the loose driver's handset that could be connected to those 2 wires, while a train was in a tunnel, to make emergency phone calls for example. But the squeezing together of the 2 wires to short out the power always seemed unlikely to me, but I never got round to having it confirmed or refuted by an expert.

So here I am 33 years later, asking, is it true or not?

And if it is true, has anyone ever done it?

I was only ever present at one police incident on underground tracks, on the Piccadilly at South Kensington, in the early 90s, and the power had already been switched off, I assume by more conventional means.

yes, I've done it, about 20 years ago, arrived at a signal failure and was unable to make contact by radio so had to take off juice to use hand set to speak to controller.  Was nervous about it but not a problem.  Wires surprisingly thick and tight when handled.  I did not feel any current.

[bassmike]

These wires are still present and working in the Thames Tunnel (L O )