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Miscellaneous: Operating Equipment & Practices

Telegraphs and Telephones: misc_equip233

Three different Great Western Railway telephones used at locations on Omnibus circuits

Three different Great Western Railway telephones used at locations on Omnibus circuits. These include a standard single button type for code ringing and below this a double button type, where an extra button was provided to dial directly to another telephone (typically the Railway Control office). This is achieved by reversing the battery polarity when the operator depresses this button, while at the Control office a polarised relay detects the reverse polarity and operates an indication lamp to draw the controller’s attention to the waiting call.

The third photograph is of an Eight-way Selective System telephone developed to avoid the incessant ringing of all the telephones on busy omnibus circuits. This used two centre-stable polarised relays with an eight way commutating switch. The switch connected a local centre-tapped battery in different ways to select one of the first ring codes as follows:

Selective Ring Code Battery Connection
+ve -ve
1 L1 L2
2 L2 L1
3 L1 Earth
4 Earth L1
5 Earth L1 & L2
6 L1 & L2 Earth
7 L2 Earth
8 Earth L2

This allowed the first number of an omnibus circuit’s telephone code to be pre-selected and only those telephones with this prefix would ring with the second number of the code when this was applied using the press button in the normal manner. It will be noted that two of the omnibus telephone cards on 'misc_equip234' have 1 – 8 prefix’s and therefore it is probable that these omnibus circuits were fitted with these eight-way selective system telephones at each location.

Robert Ferris