Shock from live rail harmless.

[Marland]

One of the FB groups I follow is about the District Railway/Line and the
historical information can be quite fascinating. Today someone posted
correspondence from the Board of Trade concerning the experimental
electric train owned by the District and Metropolitan railway that was
trialled between Earls Court and High Street Kensington . The 4 rail system
for the trial had two outside conductor rails with one at +250 and the
other -250 , the BoT considered in his report that a shock from a conductor
rail would be harmless and no worse than some experienced by some tramway
employees when they were being careless. Interesting attitude to
electrical safety compared to today.
Another interesting point was though they were happy with the position of
the conductor rails for the trial and not withstanding their opinion about
shocks the officials did ponder about the possibility of continuous
protection boards but would not be happy to see them installed if the dual
outside conductor rail position was adopted for normal use .The reasoning
was because the conductor rails had already narrowed the six foot way and
losing even more to boarding would have narrowed it too much for staff to
work in. They also used the term slipper rather than shoe for the pick
up.I actually think that is more descriptive of its function, I wonder why
it changed.
It was an interesting insight of the pioneering days of electric traction.

GH

[Charles Ellson]

Post by Marland
One of the FB groups I follow is about the District Railway/Line and the
historical information can be quite fascinating. Today someone posted
correspondence from the Board of Trade concerning the experimental
electric train owned by the District and Metropolitan railway that was
trialled between Earls Court and High Street Kensington . The 4 rail system
for the trial had two outside conductor rails with one at +250 and the
other -250 , the BoT considered in his report that a shock from a conductor
rail would be harmless and no worse than some experienced by some tramway
employees when they were being careless. Interesting attitude to
electrical safety compared to today.
Another interesting point was though they were happy with the position of
the conductor rails for the trial and not withstanding their opinion about
shocks the officials did ponder about the possibility of continuous
protection boards but would not be happy to see them installed if the dual
outside conductor rail position was adopted for normal use .The reasoning
was because the conductor rails had already narrowed the six foot way and
losing even more to boarding would have narrowed it too much for staff to
work in. They also used the term slipper rather than shoe for the pick
up.I actually think that is more descriptive of its function, I wonder why
it changed.
It was an interesting insight of the pioneering days of electric traction.

The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

[Theo]

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

The classic problematic model railway track layout being the balloon loop:
the outer rail join both poles of the inlet track causing a short. If you
insert a neutral section then you change direction when crossing the neutral
part unless you also reverse the polarity of the controls.

Theo

[nib]

Post by Theo

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

the outer rail join both poles of the inlet track causing a short. If you
insert a neutral section then you change direction when crossing the neutral
part unless you also reverse the polarity of the controls.
Theo

Hornby got that right with 3-rail! Any track layout would work, and
engines always went forwards when the controller arm was moved to forward!

nib

[Guy]

Post by nib

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

the outer rail join both poles of the inlet track causing a short.  If
you
insert a neutral section then you change direction when crossing the neutral
part unless you also reverse the polarity of the controls.
Theo

Hornby got that right with 3-rail! Any track layout would work, and
engines always went forwards when the controller arm was moved to forward!
nib

I had a Trix Twin 00 gauge model railway.

It was three rail (all insulated) and utilised (IIRC) 14V AC.

The centre rail was common and the outer rails allowed for two engines
to be controlled independently on the same track (although I guess the
"balloon" issue still applied) with one loco using one outer rail and
the other the other for supply.

Reversing was achieved by a sort of ratchet mechanism whereby power to a
loco was first cut and then reapplied.

Unfortunately in running it was not uncommon for a loco to
instantaneously lose contact and then stop and reverse of its own accord.

I eventually migrated to Hornby two rail 12V DC.

[Charles Ellson]

Post by Guy

Post by nib

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

the outer rail join both poles of the inlet track causing a short.  If
you
insert a neutral section then you change direction when crossing the neutral
part unless you also reverse the polarity of the controls.
Theo

Hornby got that right with 3-rail! Any track layout would work, and
engines always went forwards when the controller arm was moved to forward!
nib

I had a Trix Twin 00 gauge model railway.
It was three rail (all insulated) and utilised (IIRC) 14V AC.
The centre rail was common and the outer rails allowed for two engines
to be controlled independently on the same track (although I guess the
"balloon" issue still applied) with one loco using one outer rail and
the other the other for supply.
Reversing was achieved by a sort of ratchet mechanism whereby power to a
loco was first cut and then reapplied.
Unfortunately in running it was not uncommon for a loco to
instantaneously lose contact and then stop and reverse of its own accord.
I eventually migrated to Hornby two rail 12V DC.

The problem of independent control is now solved by power being always
on (just like the real thing) and a circuit board in the loco/MU.

[Marland]

Post by Charles Ellson

Post by Guy

Post by nib

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

the outer rail join both poles of the inlet track causing a short.  If
you
insert a neutral section then you change direction when crossing the neutral
part unless you also reverse the polarity of the controls.
Theo

Hornby got that right with 3-rail! Any track layout would work, and
engines always went forwards when the controller arm was moved to forward!
nib

I had a Trix Twin 00 gauge model railway.
It was three rail (all insulated) and utilised (IIRC) 14V AC.
The centre rail was common and the outer rails allowed for two engines
to be controlled independently on the same track (although I guess the
"balloon" issue still applied) with one loco using one outer rail and
the other the other for supply.
Reversing was achieved by a sort of ratchet mechanism whereby power to a
loco was first cut and then reapplied.
Unfortunately in running it was not uncommon for a loco to
instantaneously lose contact and then stop and reverse of its own accord.
I eventually migrated to Hornby two rail 12V DC.

The problem of independent control is now solved by power being always
on (just like the real thing) and a circuit board in the loco/MU.

Does make things like ballon loops easier , you still need to separate one
polarity from the other where they meet but you no longer need to stop in
the isolation section while the polarity is switched.
Though some electrical types hate the concept the first conducting wheelset
creates a short but that is detected by a circuit board in the supply that
subsequently changes the polarity in the isolated section so fast the train
and controller don’t get affected. Some of the high end controllers can be
but fortunately their trip current is usually adjustable.

GH

[Charles Ellson]

Post by Marland

Post by Charles Ellson

Post by Guy

Post by nib

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

the outer rail join both poles of the inlet track causing a short.  If
you
insert a neutral section then you change direction when crossing the neutral
part unless you also reverse the polarity of the controls.
Theo

Hornby got that right with 3-rail! Any track layout would work, and
engines always went forwards when the controller arm was moved to forward!
nib

I had a Trix Twin 00 gauge model railway.
It was three rail (all insulated) and utilised (IIRC) 14V AC.
The centre rail was common and the outer rails allowed for two engines
to be controlled independently on the same track (although I guess the
"balloon" issue still applied) with one loco using one outer rail and
the other the other for supply.
Reversing was achieved by a sort of ratchet mechanism whereby power to a
loco was first cut and then reapplied.
Unfortunately in running it was not uncommon for a loco to
instantaneously lose contact and then stop and reverse of its own accord.
I eventually migrated to Hornby two rail 12V DC.

The problem of independent control is now solved by power being always
on (just like the real thing) and a circuit board in the loco/MU.

Does make things like ballon loops easier , you still need to separate one
polarity from the other where they meet but you no longer need to stop in
the isolation section while the polarity is switched.
Though some electrical types hate the concept the first conducting wheelset
creates a short but that is detected by a circuit board in the supply that
subsequently changes the polarity in the isolated section so fast the train
and controller don’t get affected. Some of the high end controllers can be
but fortunately their trip current is usually adjustable.

With 1:1 scale the cheap and cheerful method (as with the LU/NR
interface at Queens Park) is to have enough resistance/loss in the
circuit to prevent sufficient current flowing to trip the supplies.

[Roland Perry]

Post by Guy

Post by nib
Hornby got that right with 3-rail! Any track layout would work, and
engines always went forwards when the controller arm was moved to forward!
nib

I had a Trix Twin 00 gauge model railway.
It was three rail (all insulated) and utilised (IIRC) 14V AC.

I'm currently (groan) building a 3-rail layout from scratch and have
what I believe to be an original Meccano power control unit, which says
0-12 volts DC, 8 Watts.

[Marland]

Post by Roland Perry

Post by Guy

Post by nib
Hornby got that right with 3-rail! Any track layout would work, and
engines always went forwards when the controller arm was moved to forward!
nib

I had a Trix Twin 00 gauge model railway.
It was three rail (all insulated) and utilised (IIRC) 14V AC.

I'm currently (groan) building a 3-rail layout from scratch and have
what I believe to be an original Meccano power control unit, which says
0-12 volts DC, 8 Watts.

Should be fun, there is something about the noise of the heavy diecast
Hornby stuff on its tin plate
track that gives presence and you see why it had immense play value.

I would be frowned upon by serious Dublo collectors as I have butchered
several station buildings for use outside where being alloy they are not
affected by rain ,sun etc. The signal boxes are easily cut and shut to make
housings for point motors or circuit boards.
Only ones with orange roofs though which are only a few pounds, if you find
a genuine original green roof one they fetch a lot more.

GH

GH

[Marland]

Post by Theo

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

the outer rail join both poles of the inlet track causing a short. If you
insert a neutral section then you change direction when crossing the neutral
part unless you also reverse the polarity of the controls.
Theo

Which hornby dublo 3 rail as mentioned by Charles copes with fine, it is
two rail systems that need neutral sections. DCC makes it easier as such
switching can be easily automated.

GH

[Peter Able]

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directio

Concepts like Forward and Reverse don't really matter.

The real issue is switching polarity on the fly. That was the killer
issue then. Today that issue could be addressed with a bridge rectifier
per shoe-pair.

A very common technique in squaddie-proof military wired comms!

PA
--

[Marland]

Post by Charles Ellson

Post by Marland
One of the FB groups I follow is about the District Railway/Line and the
historical information can be quite fascinating. Today someone posted
correspondence from the Board of Trade concerning the experimental
electric train owned by the District and Metropolitan railway that was
trialled between Earls Court and High Street Kensington . The 4 rail system
for the trial had two outside conductor rails with one at +250 and the
other -250 , the BoT considered in his report that a shock from a conductor
rail would be harmless and no worse than some experienced by some tramway
employees when they were being careless. Interesting attitude to
electrical safety compared to today.
Another interesting point was though they were happy with the position of
the conductor rails for the trial and not withstanding their opinion about
shocks the officials did ponder about the possibility of continuous
protection boards but would not be happy to see them installed if the dual
outside conductor rail position was adopted for normal use .The reasoning
was because the conductor rails had already narrowed the six foot way and
losing even more to boarding would have narrowed it too much for staff to
work in. They also used the term slipper rather than shoe for the pick
up.I actually think that is more descriptive of its function, I wonder why
it changed.
It was an interesting insight of the pioneering days of electric traction.

The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

Are you being serious? Full size motors don’t work like small permanent
magnet motors as the magnetic field is produced by field coils and the
relationship between field coils and armature remains the same,reverse the
current through one then it will be in reverse for the other .

Your other point would be valid if a there was a loop like the one at
Kennington as a + rail will eventually meet a -rail. The much longer lived
twin out side conductor rail example on the Great Northern and City worked
fine it but it had no such example of a loop.
The South Eastern and Chatham was considering twin outside conductor rails
one at around +600 the other at -600 to get a 1200V system ,perhaps it is
fortunate they didn’t have the money to proceed with a scheme that would
have lead to some complications.

GH

[Charles Ellson]

Post by Charles Ellson

Post by Marland
One of the FB groups I follow is about the District Railway/Line and the
historical information can be quite fascinating. Today someone posted
correspondence from the Board of Trade concerning the experimental
electric train owned by the District and Metropolitan railway that was
trialled between Earls Court and High Street Kensington . The 4 rail system
for the trial had two outside conductor rails with one at +250 and the
other -250 , the BoT considered in his report that a shock from a conductor
rail would be harmless and no worse than some experienced by some tramway
employees when they were being careless. Interesting attitude to
electrical safety compared to today.
Another interesting point was though they were happy with the position of
the conductor rails for the trial and not withstanding their opinion about
shocks the officials did ponder about the possibility of continuous
protection boards but would not be happy to see them installed if the dual
outside conductor rail position was adopted for normal use .The reasoning
was because the conductor rails had already narrowed the six foot way and
losing even more to boarding would have narrowed it too much for staff to
work in. They also used the term slipper rather than shoe for the pick
up.I actually think that is more descriptive of its function, I wonder why
it changed.
It was an interesting insight of the pioneering days of electric traction.

The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

Are you being serious? Full size motors don’t work like small permanent
magnet motors as the magnetic field is produced by field coils and the
relationship between field coils and armature remains the same,reverse the
current through one then it will be in reverse for the other .

You won't have any power for your motors when your train bridges two
adjacent sections of different polarity or gets gapped.

Your other point would be valid if a there was a loop like the one at
Kennington as a + rail will eventually meet a -rail. The much longer lived
twin out side conductor rail example on the Great Northern and City worked
fine it but it had no such example of a loop.
The South Eastern and Chatham was considering twin outside conductor rails
one at around +600 the other at -600 to get a 1200V system ,perhaps it is
fortunate they didn’t have the money to proceed with a scheme that would
have lead to some complications.
GH

[Marland]

Post by Charles Ellson

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

Are you being serious? Full size motors don’t work like small permanent
magnet motors as the magnetic field is produced by field coils and the
relationship between field coils and armature remains the same,reverse the
current through one then it will be in reverse for the other .

You won't have any power for your motors when your train bridges two
adjacent sections of different polarity or gets gapped.

That is a separate issue from your statement that the motors would behave
like Hornby Dublo ones.
If it had ever come to it then there would have been a need to have an
isolation section perhaps switchable , a similar arrangement exists where
LT*style four rail meets NR third rail with a fourth rail for LT trains
bonded to the running rails. On the Wimbledon line I think it just a long
gap but ISTR
that on the Richmond Route there is a switchable section but I could
wrong.
A shortish gap suffices on the Wimbledon route as LT stock doesn’t
have bus lines with in it.
NR stock does so a train bridging the gap could do nasty things and there
is a risk at Gunnesbury that a NR train takes the wrong road so the gap is
longer .
Rare but it does happen.
<https://www.flickr.com/photos/***@N00/6907735478/in/photostream>


* I know its not actually LT any more but the term is simple.
GH

[Charles Ellson]

Post by Marland

Post by Charles Ellson

Post by Charles Ellson
The other main snag with two outside conductor rails is that (like
Hornby-Dublo 3 rail) it isn't reversible - you can end up driving in
reverse to go forwards on bidirectional sections of track and you need
dead sections of at least a train's length to prevent bridging and/or
two ends of your train trying to go in different directions.

Are you being serious? Full size motors don?t work like small permanent
magnet motors as the magnetic field is produced by field coils and the
relationship between field coils and armature remains the same,reverse the
current through one then it will be in reverse for the other .

You won't have any power for your motors when your train bridges two
adjacent sections of different polarity or gets gapped.

That is a separate issue from your statement that the motors would behave
like Hornby Dublo ones.
If it had ever come to it then there would have been a need to have an
isolation section perhaps switchable , a similar arrangement exists where
LT*style four rail meets NR third rail with a fourth rail for LT trains
bonded to the running rails. On the Wimbledon line I think it just a long
gap but ISTR
that on the Richmond Route there is a switchable section but I could
wrong.

Manually switchable on site IIRC. When the photo mentioned below was
taken ISTR the train had to be left until the end of traffic when
suitable isolation of some LU signalling circuits was done.

Post by Marland
A shortish gap suffices on the Wimbledon route as LT stock doesn’t
have bus lines with in it.

That section also has scheduled NR services late at night.

Post by Marland
NR stock does so a train bridging the gap could do nasty things and there
is a risk at Gunnesbury that a NR train takes the wrong road so the gap is
longer .
Rare but it does happen.

Also IIRC that train had intruded too far into LU circuitry to simply
reverse back as done on other occasions. The power interface is
possibly the same as at Queens Park where brief bridging can be
tolerated.

Post by Marland
* I know its not actually LT any more but the term is simple.

[Marland]

Post by Charles Ellson

Post by Marland
If it had ever come to it then there would have been a need to have an
isolation section perhaps switchable , a similar arrangement exists where
LT*style four rail meets NR third rail with a fourth rail for LT trains
bonded to the running rails. On the Wimbledon line I think it just a long
gap but ISTR
that on the Richmond Route there is a switchable section but I could
wrong.

Manually switchable on site IIRC.

Could be , I thought that it was switched at one time when some older LT
stock did have traction bus lines between cars ,Q stock and possibly the
later flared body stocks but both have been long gone so maybe a normal
passive over one car length gap is now sufficient.

When the photo mentioned below was

Post by Charles Ellson
taken ISTR the train had to be left until the end of traffic when
suitable isolation of some LU signalling circuits was done.

Post by Marland
A shortish gap suffices on the Wimbledon route as LT stock doesn’t
have bus lines with in it.

That section also has scheduled NR services late at night.

The relevant gap is on Putney bridge , NR trains join South of the river
at East Putney.

Post by Charles Ellson

Post by Marland
NR stock does so a train bridging the gap could do nasty things and there
is a risk at Gunnesbury that a NR train takes the wrong road so the gap is
longer .
Rare but it does happen.

Also IIRC that train had intruded too far into LU circuitry to simply
reverse back as done on other occasions.

Maybe attempting to return current on LU running rails had damaged
signalling circuits,
I believe it was recovered under engineering possession using a couple of
LU battery locos .

Normally they just roll back down the gradient, one wonders why the driver
proceeded so far when it must have been obvious by then that he was off
route.

GH