UNDERGROUND CONSTRUCTION
BOX, JOINT No. 23

The number on the cover is the BT Item Code

Cover, Box Joint No. 23
Marked as "British Telcom" from 1981 and then changed to "BT" from 1996)

Cover, Box Joint No. 23
Marked at "Post Office" from 1974 until 1981

Box, Joint No. 23
Taken from Drawing CN10941 (Original dated 1974)

TELECOMMUNICATIONS INSTRUCTION
A PLANNING AND WORKS
2 External Plant
G0161
Issue 2, July 1979

BOX, JOINT No. 23

This Instruction has been REVISED and excludes reference to the Box, Joint No. 25 which is no longer available

1 GENERAL
This Instruction details the facilities offered by and installation of Box, Joint No. 23.

2 DESCRIPTION
Box, Joint No. 23 is a small prefabricated joint box for use on housing estate radial distribution schemes.

Box, Joint No. 23 is a glass fibre reinforced plastic moulding, coloured grey. It is fitted with a cast iron cover to drawing CN10939. The internal dimensions of the box are nominally 460mm long x 225mm wide x 480mm deep.

The box is designed specifically for use with one Sleeve, Polyethylene No. 31A and buried cable. Details of the use of this jointing sleeve are given in A2 H2611. Provision is made in the box for fitting the bracket CN13208 into which the Sleeve, Polyethylene will fit.

A cable entry slot is provided along the length of the base of the box which extends to form an arch in both ends. An enlargement in the slot in the base facilitates the fitting of the box over cables already jointed to a Sleeve, Polyethylene No. 31A.

Box, Joint 23 and its cover are designed to withstand pedestrian and light vehicular loading only. Installation therefore, shall take place only in foot­ways or those grassed areas within a defined kerb line.

3 INSTALLATION
3.1 Excavation
The footway material should be excavated to sufficient depth to ensure that the box cover will be level with the footway surface.

Alterations to the box position are less likely to be necessary if the joint box is not installed until the footway level is known, i.e. in most cases until after kerb stones have been laid.

The overall depth of the joint box is 490mm and the excavation should measure approx 400mm x 700mm. The base of the excavation must be free from large stones etc and should be punned flat. If soil conditions are particularly bad, a layer of sand may be spread over the base of the excavation prior to placing the box in the hole.

3.2 Cables
Where distribution cables have already been provided and jointed, no major alterations to cable positions should be necessary prior to installation of the box. The box itself, however, provides access for cables at a nominal depth of 400mm below the surface. Ideally, all cables should enter through the arches at the ends of the cabling slot. Any minor alterations to the cable positions at entry to the excavation to achieve this requirement will greatly improve the setting of the cables into a neat loop inside the box.

Where cables are laid and boxes installed at the same time, the above requirements should be born in mind. Furthermore, a cable tail of approximately 2m length must be provided for each cable to be jointed to enable the completed joint to be raised 1.5m clear above the base of the box. This facilitates the use of a jointing jig and enables the cables to be coiled neatly into the box with the joint held securely in the clamp without excessive bending of the cables.

3.3 Placing the Box
The bolt-on type sleeve mounting bracket must be secured inside the box prior to installation. Place the box into the excavation, passing all cables through the cable entry slot. For a Sleeve Polyethylene No. 31A, the clamping ring must be removed before passing the joint through the enlargement provided. Ensure that the top of the box lines up with the footway level as nearly as possible, packing under the box where necessary with additional soil or sand, punned flat before replacing the box.

3.4 Backfilling
A backfill of soil free from stones can now be punned all around the box. Care must be taken initially to avoid damage to cables. Where the footway surface has not been finished, the backfill should be built up to the top edge of the box, above the surrounding level, to give protection. Where the box is being installed into a finished footway surface, the backfill should extend up to the level of subsoil in the footway and the surface reinstated as normal.

Last revised: May 04, 2025