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:
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.
and Bell circuits were safety critical to the railways operations, these
were located on the upper crossarms to prevent spurious signals occurring in
the event of another circuits 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).
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
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.