IRON CASED, CERTIFIED FLAMEPROOF
CERTIFICATE FLP. 853
It has been specially designed for outdoor use and will be found to be particularly suitable for railway and ship-yards, docks, chemical factories, petroleum refineries, and other places where it may be exposed to inflammable vapours or atmospheric conditions detrimental to the ordinary type of instrument.
Armoured cable terminating in sealing chambers or wires in scaled screwed conduit must be used throughout a " danger zone."
The cast-iron case is watertight and the inner door is fastened by screw locks requiring a special key for opening. The outer door effectually protects the Bakelite micro-telephone and dial when not in use, and the drip-proof cowl fitted on top also protects the ringer gongs without deadening the sound.
The principle of enclosing each contact or switch point in its own flameproof chamber has been adopted, so that the effect of ignition is very small and the volume of gas involved low.
In order to prevent malicious over-rapid dialling, a specially designed coupling is arranged between the finger plate and the dial mechanism.
There is also an isolating switch which disconnects the incoming lines immediately the inner door is opened.
The apparatus, coils and wiring are specially treated to prevent detrimental atmospheric effects.
Overall dimensions 20 x 12 x 10 inches.
Note - Equivalent sets with terminating chamber suitable for Pyrotenax cable can also be
Taken from the Ericsson Telephone Catalogue, edition No. 49
Last revised: October 02, 2019