tunnel telephone wires

To refine the OP's question - I know that the TT wires CAN still be used for drivers to communicate with the line controller, but ARE they? In my experience, I can think of two occurances of the tunnel telephone being used for communication - and would question the actual benefit in both cases!

Can anyone think of recent examples where the TT was useful as a backup communication system?

Perhaps this would also help answer the original question from angelislington that the 'DRICO' system (used to communicate with the Line Controller only and NOT discharge traction current) was superseded by Train Radio.

This used the same wires as the Tunnel Telephone.

AI - if you knew what hassle it is to establish when the tunnel telephone was introduced....... Greater minds have gone on holiday to prepare for this!

DRICO - well - if you looked along the shelf to the right of the Bakerloo and Coronation notices [0], you might have found the TT instructions, and the significance of the RGIs. You are allowed to look at my library - as long as you put things back where you find them [1] - if I'd not spent so much time on Grandsire this evening I could have pointed you in the right direction.

[0] after the 1936 Coronation notices, then you get into the UERL general instructions territory, somewhere along there is a dark buff 1926 UERL appendix, and on the other side of the room above the lightswitch is the copy of JPTs book in the lightly stained camel covers..

[1] Conversation this afternoon:

AI: current rails, inside/outside/outside?
MRFS: above the wardrobe, to the left of 'Electric Trains' [2] books called 'Steam to Silver'.
AI: <plod plod, ^oooooo>
MRFS: wassup?
AI: Can't reach it.
MRFS: I'll get it for you (and does)

Spent the rest of the afternoon getting AI's chariot MoT'd whilst I was reading some LNER ScArea paperwork and AI was reading 'Steam to Silver' HFCIT!

[2] Agnew, dark green covers - a suitable 'landmark' on the shelves.

Between Aldgate and Aldgate East EB, their primary use seems to be for drying out teabags.

Actually, I should have kept quiet, took a photo and submitted that for the quiz... :-)

I don't work in the rail industry but do work in an environment where I'm involved with Life Safety and automatic switching systems as well as risk management planning.

What gives me the heebie jeebies about the process outlined above is the potential delay from the t/op attaching the handset (or, as I believe is possible, pinching the wires together to form a short) and the current being discharged - if something has been seen that needs the power cutting, I'd be looking for it to be instantaneous, not reliant on other remote human intervention.

I shuddered some more at the "7 minute rule" which effectively means that there could be an ongoing situation where the t/op and his passengers are in a tunnel section having to walk along the track and someone miles away turns the power back on - I am presenting the argument that a train could be in a long tunnel section and all means of communication have failed, including the "last resort" handset - lets say a faulty speaker or mic segment.

Are trains equipped with some sort of SCD for the TTW's? Something that needs to be physically removed before relays will close to re-instate supply? (I'm aware of the SCD's that get slapped between the current rails, but in such an emergency it may not be possible to apply this method.)

First and foremost, the procedures we use have been tried, tested, proven etc. etc. for years and years. Nothing is done lightly. No decision is simply made off the cuff.

The Delay?

From the moment the wires are pinched and rubbed, or the Tunnel Telephone has been operated, the chances are the current is either off, or possibly reduced in some circumstances. Once this stage has operated, we as controllers basically drop everything and call the Power Control Room to have the current disharged fully - this will normally take less than a minute. So in 60-90 seconds the current is fully off. Compare this with an open area that needs the current turned off fully by a call to the controller - there are no Tunnel Telephones in open sections.

The 7 Minute Rule.

Taking the stalled train scenario. Our traction current areas are relatively small, and it does not take too much time to contact each train thought to be in that section. If contact cannot be made, then ultimately it is the controller's decision to ask for a recharge after 7 minutes. Would you request that recharge?

Put simply, I want to be pretty certain I'm not about to send 630 volts into someone before I request a recharge. We don't just start the clock and when the time is up hit the button. We use the 7 minutes to contact and be contacted by anyone who may have needed the current off.

As someone who installed/maintained the Safety T/T system equipment on all lines for more than 20 years I can assure Colin that shorting the T/T wires by one of the many available methods will in fact discharge the traction current directly. As a safety system it was designed to do that and is regularly tested and maintained to a standard that achieves it.
For anyone wondering about the many ways of using the T/T system to trip out the traction supply circuit breakers let me detail them. 1. Short the wires with anything metallic 2. Pinch the wires together by hand 3. Attach the T/T handset in the driver's cab 4. Lift the handset of the headwall T/T instrument 5. Push the plunger (red button) in the headwall T/T instrument 6. use the headwall Section Ahead or Section in Rear Plunger 7. Use the station operation room Emergency T/T plunger 8. Trip the T/T section on the Service (Line) Controller T/T panel 9. Tunnel Telephone in the tunnel 10. Drop the T/T relay in the T/T relay room (may cause single end trip depending upon location) 11. Use the T/T lineman's portable T/T handset.

All the above except 10 can be done by operating staff and will remove traction current. Note that staff are normally taught to press the plunger and lift the handset of a T/T instrument, this is good practice but is 'belt and braces', either should work alone and not knowing this has caught people out who thought doing one or the other had no effect!

There are several different types of T/T system in use and several different control systems in use for monitoring them at the various Line Control Offices. In addition the Electrical Control Room Operators have white light indications on their monitoring desks to indicate tripped T/T circuits. When the T/T is operated by whatever means both the Service Controller and Electrical Control Room Operator get indications of the trip. The Electrical Control Room Operator also gets indications (red lights) for the traction circuit breakers tripped at each substation. The T/T should take out the CBs at both subs on double end fed sections (the majority of tunnel sections are normally double end fed), it will also take out track parallelling where this is used such as at Hounslow (Picc) and East Acton (Central) so the ECRO has to check the operation of CBs against operation of T/T section to be certain that traction current has been discharged from both ends and any parallelling has been taken out.
Occasionally T/T circuit wires will snap sometimes causing a single end trip, this often causes track circuit failure too as the broken wire tails recoil under tension bouncing along the tunnel contacting the running rails to the 600v and blowing track circuit fuses. there are some parts of the system more prone to this type of failure than others, places like Finsbury Park, Hatton Cross and the East London line where corrosion occurs at a higher rate due to constant running water.
In some areas such as the Heathrow Loop and Kings Cross to Liverpool Street the tunnel wires were replaced with telephones every 40 metres, this is to avoid issues of dangerous potentials as a result of faults on nearby Network Rail high voltage overhead systems. The Heathrow loop has some 120 telephones all in parallel and if any one is left off the hook following T/T operation and recharge with overriders it can be a real headache walking up to 3kM to find out which one it is so the instrument number should always be recorded when such a phone is used!

Overriders do indeed allow trains to run with the T/T out of use, all they really do is bridge out the contacts that would otherwise be opened to trip the substation traction CBs. Controllers like to run trains so often the overriders will stay in until the end of service once current is recharged with them. Sometimes this will be necessary anyway as it is usually night staff who will investigate and resolve the majority of T/T failures.

Colin mentioned enhanced line clear, this being a system that has never been fully implemented as originally proposed. The original idea was for additional protection for staff working in tunnels in engineering hours, this involved leaving the T/T in 'tripped' state at the end of traffic hours and for the staff to apply a short circuit to the tunnel wires at the work site for the duration of the work, this then would effectively prevent recharge of the traction current until the staff had vacated the worksite removing their shorting strip by drawing attention to the fact that the T/T could not be reset, requiring investigation in the same way that line clear areas must be checked for those not booking in with the Engineering Works Controller at the completion of their work to give up protection. It was quickly recognised that such a system could cause havoc, with hundreds of working parties involved on any given shift there might easily be a forgotten shorting strip left on the tunnel wires somewhere so that idea was dropped. However, it had previously been recognised that allowing such shorts would drain the batteries powering the T/T circuits during engineering hours so we spent a few months installing current limiters on every T/T circuit across the combine.
Enhanced Line Clear was responsible for the introduction of inhibitors which must be requested by the Service Controller before engineering staff are allowed to work on T/T equipment during engineering hours. Although it is not a design feature it would be possible under Electrical Control Room SPARCS (stored program automatic remote control of substations) fault conditions for the resetting of a T/T section under test during engineering hours to recharge traction, a dangerous situation. Thus CB inhibitors were introduced in order to prevent this remote possibility by effectively disconnecting the T/T CB trip circuit contacts from the substation equipment which monitors them, unmonitored is the same as tripped (open) and they need to be reset (closed) before a recharge can take place unless overridden by overriders!

There sometimes used to be some confusion in the Line Control Room when enhanced line clear was first introduced. The original procedure was for the Service (Line) Controller to use the T/T to discharge traction at the end of traffic, confirm with the ECRO that traction was discharged and then reset the T/T circuit, checking its trip & reset functions and leaving the T/T reset ready for recharge in the morning. Under enhanced line clear that altered so that the T/T was left tripped during engineering hours, as previosuly stated, following the discharge and the test of the T/T circuit functions. Earls Court had enhanced line clear on the Picc and unenhanced line clear on the District with Line Controllers wearing either hat at times and sometimes not knowing which state to leave the T/Ts in! There was also similar confusion in those early days regarding the different functions and usage of overriders and inhibitors, those of us in engineering sometimes had testing times trying to explain the necessities and differences before we could do our routine maintenance on the systems, let alone T/T Operation investigations. Things became much easier when everything became uniform under enhanced line clear.

I note MetControl's point that T/T speech to the controller is not tested often, well it should be regularly tested under the normal engineering maintenance routine. Poor speech should be logged and reported and unfortunately what is audible under test at night with no trains running is often unintelligible during the day. the Met of course is still using AFAIK one of the older T/T systems, the newest being on the Northern and JLE, next newest being on the Cental and prior to that I fitted all new phones and cabling on the Bakerloo but that was 20 years ago now! I would agree with anyone that there is room for improvement as far as the speech side of the T/T system is concerned but as a Safety System it is still the best, it is simple and it does what it says on the box! That is why it is the primary method of discharging traction current in an emergency.

MetControl said

there are no Tunnel Telephones in open sections.

Technically correct and I won't ague with it except to say that what is a tunnel for the purpose of tunnel telephone installation is important to note!

A tunnel is any enclosed section of track longer than a train length so for new work such things as motorway bridges over the railway are taken to be tunnels and should have been fitted with tunnel telephones!

One other point is that tunnel telephones can be found on platforms in open sections, White City is one such example, Baron's Court is another and I would think Finchley Road though I haven't worked there for some years now. Of course such phones are at the most convenient nearest point to the tunnel T/T section of which they form a part.

Some T/T sections are very long as far as cabling goes and very short as far as tunnel is concerned, a good example is Wood Lane to Park Royal via East Acton track parallelling hut which literally covers just a short section of tunnel from Wood Lane to White City.

RayB was worried about safety!

Don't be, the T/T system is tried and tested technology operated safely for some 85 years since initial installation in the 1920s. Used as directed and with established tried, tested and proven rules, regulations and procedures in force it remains very much fit for purpose. As far as HMRI is concerned it is not going to be replaced anytime soon, the equipment may change, indeed it has, but the system is the same.

Apologies if my original post was unclear - I didn't mean to cause offence!

I'm not doubting the value of TT for emergency discharge of traction current. My question was how often the TT is used for communication, rather than traction discharge, and excluding tests. I get the feeling that it's extremely rare, but don't know how rare.

An example of when I can remember TT being used for comms: I remember a driver waiting to be given authority to proceed past a failed signal. The initial driver/controller conversation happened over train radio, but when the driver got down to use the SPT to get authority over a secure channel, he discovered that someone had put a Herras fence in the way of the SPT instrument. Thinking laterally, he tried the TT instead, and the controller gave him authority (and a few words about how the rest of the service was now at a stand!) over the TT. (Does anyone have any thoughts as to whether TT is an acceptable secure means of communication for passing signals at danger?)

As I said earlier in the thread, my understanding was based on what I was told by my trainers during Controller training - and I also said I wouldn't be surprised if I was misinformed.

Can you see the look of surprise on my face?

Very much the technique of Sir Humphrey handling Jim Hacker in 'Yes, Minister'