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P.O. ENGINEERING DEPT
ENGINEERING INSTRUCTIONS
LINES
OVERHEAD
G3020
Issue 2, 15.3.39
LEADING-IN CABLING AT
SUBSCRIBERS' PREMISES
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. 12½ is
used for this purpose
It should be attached to masonry by means of "Lugs, Lead, 1in." (or 1¼in.),
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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