|The Main Cables leaving the exchange are fed to the
Cabinets. These are the green boxes seen in the street. In the
exchange these cables are terminated on the Main Distribution frame.
These cables are pressurised to help expel any water ingress, due to faulty joints or damage to the sheave. Replacing or repairing these cables is expensive and the pressures are monitored and an alarm sounded if pressure drops below a pre-determined level.
At the exchange the cables are feed in to the exchange via sealed ductways and then supported by cable bearers, in the cable chamber, which was under the exchange floor. They were then fed upwards to the Main Distribution Frame (MDF). The incoming ducts are shown below before any cables were drawn through.
The cable chamber, showing the cables on bearers and turning upwards
Exchange Pressure Rack. Each main cable has it's
Air compressor on rear of Pressure Rack.
Deep cable chambers called manholes were generally close to the
exchange and big enough to
Foot way joint box cover being lifted. This is the correct way, using a roller.
After lifting the cover, a gas test should take place. A miners lamp was used to test for carbon dioxide, whilst the tester above tested for explosive gases.
A footway joint box. This is a rather congested joint box but it shows how the cables are joined.
This picture shows cable creepage. This is
movement due to sloping ducts or heavy traffic.
The picture shows how the perfect joint should be made. The wires are joined by crimps. Before crimps were introduced the wires were twisted together and a paper sleeve pushed over the joint.
Last revised: March 21, 2021