Miscellaneous: Operating Equipment & Practices

Telegraphs and Telephones: misc_equip192

A close up of the telegraph line construction and the arrangement of crossing wires on photograph 'gwrl2522' to compare with the official Great Western Railway arrangement drawing (E7213) issued in 1943, confirming the second paragraph in the associated memo about ‘many variations’. In this case double J bolt brackets appears to have been attached through the ends of two of the telegraph pole crossarms, while the signal dole extension piece has a horizontal wooden crossarm with four insulators each on a single J bolt bracket in an arrangement similar to the official diagram.

All the insulators are the conventional white porcelain pot-head type and a photograph of one of these with a copper clad steel conductor is shown. At the attachment point the conductor is wrapped with a flat spiral tape to reduce potential wear and then secured around the insulator neck (groove) with a copper wire hand bind. It will be noted that the four crossing conductors are darker on the photograph confirming that these are probably the PBJ insulated conductors specified in the memo. PBJ was used prior to the introduction of rubber and PVC coverings, and the initials stand for the various concentric layers wrapped successively around the metallic conductor core – Paper (multiple oil impregnated overlapping paper tapes wound in continuous spirals provided the insulation) – Bitumen (acted as preservative compound preventing the ingress of water) – Jute (natural fibre yarn provided physical protection to the inner layers). Where PBJ conductor was used the flat spiral tape was dispensed with....

Conductors between telegraph poles were normally arranged on the crossarms in the following descending order:
Block Telegraph Circuits
Typically there were three wires for; Up Block, Down Block and a common Block return, plus a further two wires for the Bell circuit, which worked on the same wires in both directions; Bell Send and Return.
As Block and Bell circuits were safety critical to the railway’s operations, these were located on the upper crossarms to prevent spurious signals occurring in the event of another circuit’s wire failing and making contact with one of the Block telegraph wires.

Telephone Circuits (both Omnibus and Individual point to point, or exchange to point circuits)
Typically a pair of wires was required for each circuit between locations where batteries were available at each end (e.g. Signalboxes). Individual circuits to other locations (e.g. telephones at signal posts or lineside huts) required an additional pair of wires to provide power for the equipment (this pair could be shared between several locations).

Telegraph Circuits
Typically one wire per circuit with a common return wire.

Repeater Circuits, Track Circuit Indication, Route Describers and other minor Circuits
It was preferable to provide isolated discrete circuits for each of these instruments requiring a minimum of two wires. More wires would be required where circuits were electrically interlocked with other remote equipment.

Power Lines for trickle charging remote batteries (typically powered switches and signals) and for remote mains power (e.g. electric illumination)
These circuits were normally arranged in pairs with the live wire insulated (PBJ). It was also common to see these wires attached to brown porcelain insulators. These insulators had a higher electrical withstand level and provided a visual indication to linesmen.

Robert Ferris

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