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Issue 2, 15.3.39


1. General
This Instruction relates to leading-in from open wires at subscribers' premises. The cabling should not, in general, extend to a point beyond the reach of a 30ft. ladder.

2. Cable, I.R.V. Core, T., 1-pr. 12 is used for this purpose
It should be attached to masonry by means of "Lugs, Lead, 1in." (or 1in.), spaced at 9in. intervals on horizontal runs and at 12in. intervals on vertical runs. It is usually practicable to drive the lugs direct into the mortar courses of the masonry; when hard cement mortar is encountered, it will be necessary to resort to plugging, either with wood plugs, or Rawlplugs.

3. Leading-in cabling on walls of buildings should be unobtrusive
As far as possible, cable should be run under the eaves, in angles formed by the masonry, beside rain-water pipes, and in similar inconspicuous positions. Advantage should be taken of architectural building lines; for instance, where projecting courses of brickwork have been introduced, the cable may be run along the shelf formed by the topmost course; where ornamental timbering exists in suitable positions, the cable may be run close alongside (but not on the face of) the timbering.

4. Where it is necessary to fix the cable without concealment on unbroken surfaces of masonry, it should be accurately run in horizontal or vertical lines. Care should be taken to avoid sagging between adjacent lead lugs. The cable should not bear on sharp angles or projections on the face of the wall. All bends should be easy. Where the cable makes a right-angle bend, it should not be bent sharply round a lead lug; the bend should have at least a 2in. radius, and the adjacent lugs should be affixed just clear of the curve.

5. Leading-in cables on tiled or slated roofs
It is sometimes necessary to terminate a spur on a chimney bracket, and to run the leading-in cable down the roof, over the eaves and down the wall to the leading-in point. In such cases, it may be impossible to obtain fixtures for the cable between the base of the chimney and the top of the wall; care should, therefore, be taken to run the cable where it will be least liable to disturbance, and where it will not bear on sharp edges of tiles, masonry, etc.

6. Where it is impossible to avoid sharp edges e.g. at the eaves gutter, strips of lead should be interposed to prevent cutting of the cable sheath.

7. Holes for leading-in
Holes cut through window or door-frames or other parts of a building for leading-in should be bored in a direction sloping upwards from the outside surface. This will prevent the ingress of moisture.

8. Leading-in near "Neon" or similar type signs
Luminous-discharge tubes, such as "neon" signs, usually operate at a high voltage, and there is some risk of the sheath of the high-voltage cable and other metalwork of the sign assuming a dangerous potential above earth. Contact between this metalwork and P.O. cables must be avoided; leading-in cables should therefore be given as great a clearance as practicable from such a sign and should preferably be run below it. In no case should the clearance be less than three inches.

9. Precautions to be observed when working in the vicinity of high-voltage signs are detailed in J 1201.

10. Treatment of existing installations
It is not intended that any special investigation should be made with a view to bringing existing installations into line with this Instruction, but the opportunity should be taken during maintenance visits and at other convenient times, to notice whether the foregoing conditions are complied with, and, if they are not, to arrange for the necessary alterations to be made to the P.O. plant. Where, however, there is reason to believe that in any particular case the existing conditions are dangerous, the matter should receive immediate attention.

Drop-wire feed and Lead-in - dated 1933



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Last revised: March 30, 2023