What is the purpose of a rail gap indicator..?

[paterson00]

Other than to indicate a rail gap..

I've just come from Network Rail so all this is new to me and i will have loads of questions like this for about a year or ten..

[mrfs42]

Jun 24, 2009 5:21:56 GMT @paterson00 said:

Other than to indicate a rail gap..

I've just come from Network Rail so all this is new to me and i will have loads of questions like this for about a year or ten..

If the lights are lit, the current on the far side of the gap is OFF. I've heard the phrase 'cherries' used as in 'The cherries are on, mate'. Comes from the three red bulbs....

There are also rail gap indicator repeaters, to give advance warning.

[Phil]

Yup - it's effectively a STOP signal (because you can't go any further anyway).

[citysig]

Jun 24, 2009 8:28:54 GMT Phil said:

Yup - it's effectively a STOP signal (because you can't go any further anyway).

... because you shouldn't try to go any further ;D

[Deleted]

Jun 24, 2009 9:14:46 GMT @citysig said:

Jun 24, 2009 8:28:54 GMT Phil said:

Yup - it's effectively a STOP signal (because you can't go any further anyway).

... because you shouldn't try to go any further ;D

And if you did, you'd be done for a SPAD, IIRC.

[paterson00]

Does that mean then, that sometimes during traffic hours that the current is turned off? I assumed it would be on all the time until engineering hours. If it gets turned off during traffic hours what might be some reasons for this

[pakenhamtrain]

The traction current would be turned off for a Person under, train derailment and so on(I'm open for correction on that)

[North End]

Jun 24, 2009 8:28:54 GMT Phil said:

Yup - it's effectively a STOP signal (because you can't go any further anyway).

Not quite a stop signal, because if unable to stop in time, Train Operators are authorised by the Rule Book to coast the whole of their train over the gap.

As to when you'd see one lit in Traffic Hours, examples are:

1) When current has been discharged due to spurious TT activation (like happened on the Northern Line between South Wimbledon and Morden today)

2) Traction current discharged due to incident / emergency (person on the track)

3) Defective RGI

4) Traction current discharged over a section to which points are set, but not the route the train will be taking (e.g. East Finchley Platform 2 early in the morning, when current is switched on for the northbound, but not yet for the southbound, the RGI will be extinguished only when the signal route is set and the points thrown).

5) Traction current not yet switched on to the section ahead because your train is running early (I've seen this happen at Finchley Central).

Those are probably the most common reasons, there are others.

[happybunny]

We are told to MOTOR over rail gaps if we can't stop in-time, to get to the dead section now.

[Deleted]

To add one on to North End's list, RGI's also illuminate when they are too many trains in a section and the circuit breakers kick in.

[Colin]

Jun 24, 2009 11:26:04 GMT @theonekea said:

And if you did, you'd be done for a SPAD, IIRC.

Yes and no.

It is a SPAD, but it's a category C (**I think**) - point is the train op cannot be 'done' for it.

Jun 24, 2009 16:08:24 GMT @happybunny said:

We are told to MOTOR over rail gaps if we can't stop in-time, to get to the dead section now.

Or otherwise seek permission from the controller to motor if you are stopped across a gap.

[Deleted]

A Rail Gap Indicator or RGI is a stop signal as it displays a red aspect to on coming trains, although it can't physically stop a train. Depending on the circumstances it can be a category A or B SPAD, and if you stall and bridge a rail gap you will 'juice up' or liven the dead section. They normally have plenty of sighting distance (including the addition of a repeater) so you should be able to stop prior to the RGI, but if traction current is discharged whilst you are approaching an RGI, as a T/Op you must decide if you can stop prior to the RGI or if you need to motor up to fully pass over the gap and not bridge the gap, which would result in the dead section becoming live. If you did bridge the gap you would be asking the controller to discharge the section at the rear, not to pass over it.

[Tom]

Jun 24, 2009 16:13:47 GMT @upinthesky said:

To add one on to North End's list, RGI's also illuminate when they are too many trains in a section and the circuit breakers kick in.

i.e. Traction Current discharged on overload.

[Tom]

Jun 24, 2009 16:08:24 GMT @happybunny said:

We are told to MOTOR over rail gaps if we can't stop in-time, to get to the dead section now.

But surely that will (theoretically, at least) liven up the dead section whilst the train is passing over the gap?

I would also agree that it could be treated as a Category A or B SPAD, depending on the circumstances.

[setttt]

Jun 24, 2009 18:33:49 GMT Tom said:

Jun 24, 2009 16:08:24 GMT @happybunny said:

We are told to MOTOR over rail gaps if we can't stop in-time, to get to the dead section now.

But surely that will (theoretically, at least) liven up the dead section whilst the train is passing over the gap?

I think the chances of that happening are pretty much nil unless the rail gap is less than a cars' length (I don't know if there are any examples?). Either way it is a rule book requirement.

By the way there is no requirement to specifically seek permission from the controller to motor off a gap if your train becomes stopped over one, however you must ask the controller to switch off the live section if unable to motor across.

[Deleted]

Jun 24, 2009 18:33:49 GMT Tom said:

Jun 24, 2009 16:08:24 GMT @happybunny said:

We are told to MOTOR over rail gaps if we can't stop in-time, to get to the dead section now.

But surely that will (theoretically, at least) liven up the dead section whilst the train is passing over the gap?

I would also agree that it could be treated as a Category A or B SPAD, depending on the circumstances.

On the older stock you were advised to Motor up and then shut off prior to the gap, trip your 'MG's' and cut out the Compressor Governor in the leading cab. By doing this you are isolating all of the 630v equipment on the train from drawing current and reducing the chances of 630v being transfered to the 'dead' section via the train. On the modern stock you would put the TBC in 'off and release', trip your overloads and coast across the gap until you believe you have cleared the gap and signals permitting , try and reach the next station.

[Colin]

Right, first of all SPAD Categories are:

Category A - Any SPAD when a stop aspect or indication (and any associated preceding cautionary indications) was displayed correctly, in sufficient time for the train to be stopped safely at the signal.

Category B - Any SPAD where the stop aspect was displayed because:

• signalling or level crossing equipment has malfunctioned
  
• it was returned to danger in error
  
• train bourne equipment has failed to interpret the correct signalling commands

Category C - Any SPAD when a stop aspect or indication was not displayed in sufficient time time for the train to be stopped safely at the signal (ie, returned to danger because of an emergency).

Category D - When vehicles without any traction unit attached or a train, that is unattended, runs away past a signal which is at danger. If the vehicles involved are being propelled and ran away because the movement wasn't controlled, the incident must be treated as a category A SPAD.

Those are the definitions as per LU's SPAD policy - so how can an RGI illuminating be category A or B when it is quite plainly category C?!!!

Moving on, to the traction current gap itself and the position of a given train...........

Trains used to have bus bars running along the length of a train which meant they could easily bridge a gap between a live & dead section. Modern trains do not have this and so the motor cars are essentially separate from each other, thus the risk of bridging a gap is extremely low and that is the basis for the current rules...

Rule book 7 (Train incidents and safety equipment), section 6 (Loss of Traction Current):

6.1 If a rail gap indicator is illuminated

When a rail gap indicator is illuminated, you must try to stop the
train at the rail gap indicator. If you cannot stop the train, you must:

• motor or coast across the current rail gap (to the next station or as far as signalling permits)
  
• use pop whistles when approaching blind areas and station platforms.

In all cases when your train has stopped you must:

• tell the controller
  
• carry out the instructions you are given
  
• tell the customers what is happening.

So that's that sorted then - proof we can indeed motor across a gap when the RGI is illuminated.

6.2 When traction current is switched off in the section the train is occupying

If you become aware that traction current has been switched off from the section that your train is occupying, you must:

• try to coast to the next station or as far as signalling permits (even if this means coasting into a live section and proceeding normally)
  
• use pop whistles when approaching blind areas and station platforms.

In all cases when your train has stopped you must:

• tell the controller
  
• carry out the instructions you are given
  
• tell the customers what is happening.

When you are coasting within a dead section and you see an illuminated rail gap indicator, you must:

• try to coast across the current rail gap, to the next station (or as far as signalling permits)
  
• tell the controller
  
• tell the customers what is happening.

If your train comes to a stand where traction current has been switched off, you must contact the controller using any means of communication available.

6.3 Bridging a current rail gap

If your train stops and you become aware it is bridging a traction current rail gap between a live and a dead section, you must:

• try to motor across the gap, or
  
• ask the controller to switch off traction current for the live
  section, and confirm when this has been done.

Now this is where I would suggest there has been a minor change to the rules - either that or we have been told the wrong thing during annual refresher training. I'm sure you are supposed to contact the controller for both of these (6.3), and it is then up to the controller whether they want you to motor across or whether they want to take off the section behind. Point is the current is off for a reason and they may want you to stay where are and take off the section in rear instead.

Hmm....

[Deleted]

Jun 24, 2009 20:10:30 GMT Colin said:

Right, first of all SPAD Categories are:

Category A - Any SPAD when a stop aspect or indication (and any associated preceding cautionary indications) was displayed correctly, in sufficient time for the train to be stopped safely at the signal.

Category B - Any SPAD where the stop aspect was displayed because:

• signalling or level crossing equipment has malfunctioned
  
• it was returned to danger in error
  
• train bourne equipment has failed to interpret the correct signalling commands

Category C - Any SPAD when a stop aspect or indication was not displayed in sufficient time time for the train to be stopped safely at the signal (ie, returned to danger because of an emergency).

Category D - When vehicles without any traction unit attached or a train, that is unattended, runs away past a signal which is at danger. If the vehicles involved are being propelled and ran away because the movement wasn't controlled, the incident must be treated as a category A SPAD.

Those are the definitions as per LU's SPAD policy - so how can an RGI illuminating be category A or B when it is quite plainly category C?!!!

If a train passed an illuminated RGI that was attached to a signal post for a station starting signal that at the time was showing a green aspect (as RGI illuminating do not put signals back to danger) or was fixed to a post that was clearly visible to a T/Op who was berthed at a platform, then would criteria of a Category C SPAD still apply? You can never assume that passing a RGI illuminated at danger will always be classed as category C SPAD, as it depends on the location of the train at the time of the incident.

[Deleted]

If a driver passes a rail gap indicator that was illuminated in sufficient time for that train to have been stopped the it is a Cat A SPAD, unless the display was caused by faulty equipment when it is a Cat B SPAD.

If the driver passes a rail gap indicator that is illuminated too late for the train to be stopped then it is a Cat C SPAD.

There are sighting issues for a number of RGIs however.

If there are any locations left where it is possible to bridge a rail gap (I don't know of any ... and either way it'd take some establishing that you were, in fact, doing so !!)) and one should end up in that situation, I can not conceive why you wouldn't just use the motor car on the live bit to either move fully off traction current or fully on traction current. (No need to contact the controller)

Colin has fully covered off the governing rules.

[North End]

Jun 25, 2009 2:55:09 GMT @aspect said:

If there are any locations left where it is possible to bridge a rail gap (I don't know of any ... and either way it'd take some establishing that you were, in fact, doing so !!)) and one should end up in that situation, I can not conceive why you wouldn't just use the motor car on the live bit to either move fully off traction current or fully on traction current. (No need to contact the controller)

I'm pretty sure there are still some short gaps on the Northern Line. Lambeth substation gap springs to mind as one location. Also I'd suspect there are a few places where you pass from the n/b to s/b sections at crossovers.

[mrfs42]

I think Lambeth North southbound is still a 48' gap.

[Deleted]

Jun 25, 2009 3:52:20 GMT North End said:

Jun 25, 2009 2:55:09 GMT @aspect said:

If there are any locations left where it is possible to bridge a rail gap (I don't know of any ... and either way it'd take some establishing that you were, in fact, doing so !!)) and one should end up in that situation, I can not conceive why you wouldn't just use the motor car on the live bit to either move fully off traction current or fully on traction current. (No need to contact the controller)

I'm pretty sure there are still some short gaps on the Northern Line. Lambeth substation gap springs to mind as one location. Also I'd suspect there are a few places where you pass from the n/b to s/b sections at crossovers.

Still plenty of locations around where there is no RGI, despite there being current rail gaps.

[citysig]

Jun 24, 2009 14:20:17 GMT pakenhamtrain said:

The traction current would be turned off for a Person under, train derailment and so on(I'm open for correction on that)

Jun 24, 2009 18:32:56 GMT Tom said:

i.e. Traction Current discharged on overload.

Let's not be so pessimistic. Sometimes there are perfectly reasonably planned traction current discharges in traffic hours. It's not always a dramatic, system breaking down, end of the world event to see an RGI illuminated.

[Deleted]

Jun 25, 2009 11:12:22 GMT @citysig said:

Jun 24, 2009 14:20:17 GMT pakenhamtrain said:

The traction current would be turned off for a Person under, train derailment and so on(I'm open for correction on that)

Jun 24, 2009 18:32:56 GMT Tom said:

i.e. Traction Current discharged on overload.

Let's not be so pessimistic. Sometimes there are perfectly reasonably planned traction current discharges in traffic hours. It's not always a dramatic, system breaking down, end of the world event to see an RGI illuminated.

You obviously haven't driven a train a full speed then come around a corner and found one illuminated, leaving you very little decision and stopping time!! ;D ;D

[memorex]

Jun 25, 2009 11:11:55 GMT @linecontroller66 said:

Still plenty of locations around where there is no RGI, despite there being current rail gaps.

Are locations with gaps in the current rails but no RGI not just places to break up one section into smaller sections via the section switches?
It is my impression that an RGI is not needed here as, if current is taken off for any reason for the section, both sides of such a gap will be dead.
If the section switches are open and one side is live and the other is not, the member of staff opening the switch has been instructed to place a red light on top of the section switch box facing the track, and another in the four foot facing the direction of approaching trains, meaning an RGI is not needed?

[Colin]

As linecontroller66 has already said, not all traction current section gaps have RGI's. Where there are RGI's, they are only at the start of traction current section.

Section switches (to the casual observer this may look like two Yellow boxes side by side at intervals along the track) do indeed break traction current sections into smaller parts....however they are generally only used following some incident on the railway, or as part of the protection arrangements for engineering works - so RGI's are not warranted.

There are other types of switches that may also resemble a section switch, but the indication of operation is always the same - a red flag or lamp at the base, pointing across the track. Only if a train is required not to pass the switch will a second red flag or lamp be placed in the four foot (middle of the track).

[mrfs42]

I suppose it means the difference between sectionalisation gaps as pushed by Dell et al, current rail gaps that are permanently coupled (ie. no switch) and current rails that have expansion gaps.

[Colin]

Disclaimer - I must stress that I'm fairly certain I'm right in what I'm saying within this post regarding bus bars, earth faults and sectionalisation gaps, but I am open to correction.....

Traction current sections are usually double end fed - a fictitious example:

Sloane Square to Westminster. There will be a feed from both the Sloane Square and Westminster sub stations to both ends of the traction current section. The next traction current section could be Westminster to Blackfriars, with the same set up. There'll be a bus bar in Westminster sub station which means both traction current sections will get a feed off the same supply at Westminster sub station - and can pass earth faults from one traction current section to the next.

Sectionalisation gaps mean there is no bus bar in the sub station, and thus the two adjacent traction current sections are independently fed - they're completely separate and no faults can pass through.

Sectionalisation gaps can cover several traction current sections with both the line controller and the power control room having a tapping on different traction current sections. By opening and closing certain circuit breakers in the sub stations, and using the readings on their respective equipment, it's possible to trace an earth fault to a particular traction current section.

As for 'current rail gaps that are permanently coupled (ie. no switch)' - surely it's not a rail gap if it's permanently coupled with no switch?!!

Whilst I wouldn't profess to know what the ideal length is, I wouldn't imagine expansion gaps are long enough to qualify as useful for anything - except perhaps a section switch gap at a push.

[mrfs42]

Jun 27, 2009 23:56:49 GMT Colin said:

As for 'current rail gaps that are permanently coupled (ie. no switch)' - surely it's not a rail gap if it's permanently coupled with no switch?!!

I was thinking more of the rail gaps on the Central that are still there - eg White City where there are coupling gaps, plus gaps for the train stops. There is a physical gap in the current rail but the rails are connected by jumpers. Bayswater - Paddington sewer gap, subway gaps at ?Chorleywood, unswitched gaps between the Claphams; floodgate gaps too.

Obviously, you can't isolate without disconnecting the jumpers. I did mean to amplify what I said a bit more - think I pressed 'send' too soon, apologies.

However, these can, in dire emergency, be disconnected once the juice is off both sides - then reenergised so the current rails are live up to the normally jumpered gaps IYSWIM.

[railtechnician]

Interesting that in this entire thread no-one seems to have mentioned switched RGIs as such although the SPAD rules allude to them. Places like Acton town spring to mind where the RGIs circuits are routed over the points and switched when the points are thrown. I don't think it's an issue these days with the policy of taking off current to parallel sections at the same time (I believe that is still the case but I'm out of the loop being retired) but in the days when no such rule applied I think it was possible for RGIs to give apparently incorrect indications.