UNDERGROUND CONSTRUCTION
CABLE PRESSURE

The main cables from an exchange are dry air pressurised, to prevent ingress of water, and as they were expensive cables, the less joints means literally no maintenance.  It was found that if the cable leaked, the pressure would generally be enough stop any water entering the cable to far  until the leak was repaired. 

There is usually an air pressure rack in the local exchange and this rack has a desiccators, air gauges and air adjusters on it.

In reduction in air pressure would operate an alarm in the exchange.

Cable Pressure rack

Engineer adjusting the alarm setting on a pressure gauge.
The desiccator is at the bottom of the rack with the pressure adjusters are just above.

Last revised: April 05, 2023