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Telegraph Poles, Cable Conduits and Switch Boxes

To carry the telegraph and telephone signals and electrical block instrument signals the railways had to run wires alongside the track. Prior to the second world war electrical wires had to be insulated using natural rubber or material such as gutta percha, both of which degraded over time, hence it was more economical to suspend telephone and telegraph wires from glass or ceramic insulators on the lineside telegraph poles. Gutta Percha is a rubber-like Malayan gum obtained from trees which is liquid when heated and solid when cool. It is an excellent insulator and was used as the main cable insulation for underground and under sea cables for many years.

This topic came up on the uk.railway newsgroup so I asked if the system used an earth return (requiring a single wire) or a pair of wires to get an idea of how many wires would be appropriate for a branch line. The reply from one of the regulars on the group answers both questions rather well

- Do block instruments and single stroke bells use earth
- return (requiring only one wire) or do they all require
- a pair of wires? I was wondering how many wires would
- run alongside a 'typical' branch line.

Originally *everything* used Earth return (later many places had a metallic common return, still used in some places). Typical Block rig was Up Block, Down Block, Bell.
Signal arm and light repeaters also used Earth return.
Telegraph pole routes typically used 200lb (per mile) copper wire, more for mechanical strength than conductivity, so as can be imagined this was rather costly to begin with, and providing individual returns would have doubled this.
By contrast, modern railway telecomms cables (which we signalling types sometimes use for our stuff as well) have cores of 20lb, 88 ohms per loop mile (just one of those values imprinted on my brain from years back !).
When metallic returns (line wires or cable cores) started to be used, block and bell often had their own, so you would have Up Block, Down Block, Block Ret, Bell, Bell Ret.
Note that the bell circuit works in both directions over one wire. At each end, the Tapper key Normal (released) connects the line to the bell, and the battery + there is disconnected, and when pressed, disconnects the bell and puts the battery + to line, ringing the bell at the other end. If the keys at both ends are depressed together, both batteries' + are put to line and just oppose each other, though some current will flow if they are of different voltages.
Using E or common return can cause some interesting effects if it gets disconnected somewhere, as the current can find another path back to the battery via some other equipment, which may than operate unexpectedly. Many, many years ago, I was tracing wires in an old cable cupboard on the end wall of the signal box, prior to it being replaced, when the signalman called down "What the ____ have you done ?!". He had pegged LC on one block instrument, and all four needles (two pegger and two non-pegger for two pairs of running lines) in one direction were showing partial "Line Clear". Somewhere in the cable cupboard, a return connection had gone high resistance, but electricity is funny stuff and it had found another way 'home', backwards and forwards between the two signal boxes through all needles in series.
These days we usually have plenty of cable cores available to us, the major cost is in the route (troughing, direct burial etc), the cost difference between 27 & 37c signalling, or 20 and 30 pr tele cable is tiny compared to the cost of actually installing the cable (of any size), so the preference is for separate metallic returns for all circuits.

Wobbly Bob

From which it would appear that the average branch line should have five or seven (including telephone) wires running along beside the track. On main lines there would be several pairs, trunk routes often had upwards of thirty pairs of wires running along beside the track. The rhythmic dipping of the suspended wires seen through the window was rather hypnotic and formed an enduring memory of train travel up to the 1970's. At one time the railway leased spare capacity on these lines to the General Post Office (British Telecom was only separated from the Post Office in 1984) for their telephone and telegraph traffic.

There are plenty of commercial sources of telegraph poles, the softer plastic type are less susceptible to damage. These can be 'strung' with fine mono-filament fishing line but this has no 'dip' between the poles. With care 5 Amp. fuse wire can be used but this in turn is much more liable to accidental damage when the Big Hand from the Sky reaches in to retrieve a derailed wagon or clean the track.

Following the war, during which new insulating materials such as polythene were developed (polythene had been invented in by R.O. Gibson working for ICI at Winnington in Cheshire in 1933 but was not adopted for electrical insulation for several years), it became cost effective to replace the bare wires suspended from telegraph poles with insulated cables. Where these cables are run in the open, with no convenient wall to mount the clips on, they are carried in a white concrete rectangular tube run along the line side. This conduiting was a standard size, roughly six inches wide by nine inches deep and came in standard lengths. In some locations more than one was required to carry all the cables. These conduits were initially supported about every four feet on a concrete pillar and occasional sections would be broken or missing, revealing a group of wires sagging down. Metal clips were used to hold the 'lid' on the top, although this also was often missing. The metal clips tarnished over the years to quite a dark brown colour. Where the conduit ran along platforms and the like it was laid on the ground, often half buried in the ballast beside the track and by the 1980's the standard practice seems to have been to run all the conduiting along the ground. More recently (since about 2003) there seems to have been a shift to using metal conduiting, roughly the same size as the old concrete type but much thinner walled and lacking the cover or top.

Fig___ Cable conduits

Photos and sketches showing Cable conduits

The telegraph poles were gradually replaced by these conduited cables and had largely disappeared by the early 1980's.

Heavy power cables for use on the electrified lines and power cables feeding electric signals and points were often suspended from abutment walls and the like using U shaped metal clips. The cables were generally rather dark grey in colour and about two inches (5cm) in diameter.

Electric point control, point heating (for winter) and electric light signalling systems all require track side relay boxes and since the 1950's these have been fairly standard, an example is shown in the picture above. These track-side electrical boxes are usually painted light grey and, when positioned between the tracks, they sometimes stand on short legs to raise them above the ground. You will see a lot of these on the modern railway, for example a single point at a remote single track junction would typically have three; one for the point motor control, one for the point heating circuits (used in winter) and a third for the local 'track circuits'. Models of these boxes are available commercially (Langley offer a pack of three in white metal) but they are not difficult to scratch build.

One side effect of the change to digital control system is a reduction in the size of the relay boxes beside the tracks. The new boxes are small and T shaped, standing only about two feet high. As with the older relay boxes they stand on a concrete platform, set back slightly from the track.

Fig___ Modern solid state relay box
Photo of Modern solid state relay box

This single small box replaced two of the older type illustrated above.

There are also larger installations, the example shown below is at Stockport and forms part of the track redsign and resigalling in about 2005. The photo was taken in 2007. Note the air conditioning unit mounted low down at the end, also note the elderly 'yard lamp' still in position and possibly in use.

Fig___ Modern signalling system, portable switch room.
Photo of Modern solid stateportable switch room with air conditioning

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