The Joint Box

This is an underground structure where the underground cables are joined.  They are normally constructed on the surface, which are called footway boxes, with deep level chambers called manholes.  The deep level manholes are generally in the centre of big cities and are not built much today.  This is due to the dangers of gas when working underground, the cost of construction and safety issues.  The surface level joint boxes have none of the inherent dangers of the manhole, except that they must be cordoned off to prevent pedestrians from falling into the hole!

The covers are specifically made for either footway boxes, carriageway boxes or manholes.  Carriageway boxes will take all traffic whilst footway boxes are not designed for traffic. 

Joint boxes are used where ever a cable needs to be joined.  The GPO would pull through the longest possible length of cable to reduce the joints - this is to make the cable more reliable and the cost would be reduced.

From the Exchange to the Cabinet the joints would mostly be through joints, but between the Cabinet or Pillar and the distribution points the joints would have a number of outgoing cables.

Click here for a description of Manhole/Coinbox covers

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 Lamp, Safety No. 1A (miners lamp) was lowered into the chamber to test for carbon dioxide, whilst the Indicator, Gas No. 5, shown above, checked for explosive gases.

Gas plumbing a joint in surface box (Picture taken 1956)

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.
In these cases the cables would be anchored to prevent them from moving.
 

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: August 06, 2025