OVERHEAD CONSTRUCTION
OPEN-WIRE ON BUILDINGS & BUILDING FIXINGS


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P.O. ENGINEERING DEPT
ENGINEERING INSTRUCTIONS
LINES
OVERHEAD
E3142
Issue 1, 19.8.36

OPEN-WIRE DISTRIBUTION
Wiring on Buildings

1. General
This Instruction relates to spans of wire terminated on house fixtures at both ends. (For leading-in cabling, see G 3020).

2. Open wiring on buildings
Since the fixtures are rigid and the spans generally short, vertical formation of the wires, though desirable, is not essential. Where the spur from the pole line reaches the building in vertical formation, the wires should continue in vertical formation on "Spindles No. 7" (see Fig. 1). Where the span length between house fixtures does not exceed 20yds., however, the wires may be run on "Spindles No. 4A" fitted to "Brackets No. 2" if this course presents advantages.

3. Open-wire leads from chimney attachments
It is sometimes necessary to extend a spur from a chimney fixture, via an eaves bracket, to a leading-in point on the front of a building (see Fig. 2). In such a ease, the wires will make a quarter twist between the "Spindle No. 7" on the chimney fixture and the two "Spindles No. 4A" on the eaves bracket, and will be continued thence in parallel formation to the leading-in point. The leading-in insulators, "Insulators No. 21" should be fitted on a "Spindle No. 10" attached to a suitable wall fixture; "Insulators No. 10'" should be fitted at the eaves bracket. The side knobs of the "Insulators No. 10 and 21" should be arranged to give the maximum separation between the two vertical drop wires. Extra insulator rings may be fitted, if necessary, to ensure that the insulators, when screwed down tightly, are in the correct position.

FIG. 1
SINGLE CIRCUIT RUN ON SPINDLES No. 7, ON BRACKETS No. 5



FIG. 2
OPEN-WIRE LEAD-IN FROM CHIMNEY FIXTURE

4. This method of leading-in is expensive in that numerous fittings are required, and it should not be adopted without good reason. If the termination of the spur from the pole can be reached by a 30ft. ladder, an open-wire drop should not be used. The cable lead should commence at this point.

5. Parallel Circuits
It is often necessary to lead two pairs of wires from a pole line, via one or more house fixtures, to the same leading-in point. Unless the spans between house fixtures are very short - i.e., under 20yds. - such circuits should not be run parallel on "Spindles No. 7" fitted side by side in "Brackets No. 2"; if this is done, the horizontal clearances are small and it is seldom possible to place the inner "Spindle No. 7" in such a position that it will not tend to shift under the stress of the wires.

6. Where the span lengths are greater than 20yds., the circuits should be run one above the other on separate wall fixtures. The attachment of additional spindles to "Brackets No. 5" by means of terminal irons, is not permitted.

7. Overhouse work is seldom required with present-day methods of distribution, but where unavoidable, it will generally be found most convenient to attach the circuits to chimney brackets. On roofs which are constructed with a ridge of sheet zinc or galvanized iron, it is possible to obtain an attachment by means of "Spindles No 3". Such fixtures should, however, be avoided as far as practicable, as there is a risk of leaky roofs resulting.


P.O. ENGINEERING DEPT
ENGINEERING INSTRUCTIONS
LINES
OVERHEAD
E3134
Issue 1, 19.8.36

OPEN-WIRE DISTRIBUTION
Running Subscribers' Spurs - House Fixtures

1. Choice of position
In selecting the positions for house fixtures, consideration should be given to the following:-

  1. The clearances stipulated in B1301 should be observed.
  2. The fixtures should be easy of access by workmen.
  3. The fixtures should be as near as possible to the leading-in point, so as to avoid the use of a long cable-lead.
  4. Wires should be run so that they do not pass directly in front of windows, and are otherwise as unobtrusive as possible.

2. Wall fixtures
The wall fixtures to be used for terminating subscribers' spurs are "Spikes, Insulator, No. 1" and "Brackets Nos. 2, 5 and 10". The use of these attachments is illustrated in Figs. 1 to 5.


3. "Brackets Nos. 2 and 5" and "Spikes, Insulator, No. 1"
The insulator spike (Fig. 1) affords the simplest means of attachment to ordinary brickwork or masonry, and should generally be adopted where the angle between the wires and the face of the wail does not exceed 60°. Mechanically, a wall fixture is at its weakest when the wires pull directly away from the wall; when this condition obtains, a spike should not be used. As an alternative, it will usually be possible to obtain a fixture at a corner, in which case a "Bracket No. 5" (see Fig. 2) should be used, the longer arm being placed so as to take the greater share of the strain.

FIG. 1
WALL FIXTURE - SPIKE, INSULATOR, No. 1 (Angle ABC not more than 60°)
 

FIG. 2
CORNER FIXTURE - BRACKET No. 5

4. When it is necessary to clear small projections at the wall or at the eaves, a "Bracket No. 2" should be used ; the spindle being placed in the outer eye, as shown in Fig. 3.

FIG. 3
CORNER FIXTURE - BRACKET No. 2 (DOUBLE BRACKET) EMPLOYED TO OBTAIN CLEARANCE WHERE
PROJECTIONS FROM WALLS EXIST
 

5. When it is impossible to avoid running wires approximately perpendicular to the face of a wall, and a corner fixing cannot be obtained, a "Bracket No. 5" should be opened out and fixed flat against the wall as shown in Fig. 4.


FIG. 4
WALL FIXTURE - BRACKET No. 5 FLAT ON WALL (WIRES APPROXIMATELY AT RIGHT ANGLES TO WALL)
 

6. Bracket No. 10
Where a substantial facia board or stout timbering is available, a "Bracket No. 10" may be used with advantage, irrespective of the angle that the wire makes on the wall (see Fig. 5).

FIG. 5
FIXTURE ON TIMBERING - BRACKET No. 10

7. Chimney brackets
Wires should be terminated on chimneys only as a last resort, when it is impossible to obtain adequate clearance in any other way. The brickwork of stacks is readily damaged, and great care is necessary to avoid breaking slates or tiles when working on a roof. A fixture should never be made on an unsound stack. On a tall narrow stack, the attachment should be not more than one-third the height of the stack from its base.

8. When a chimney attachment is unavoidable, a "Bracket No. 6" should be fitted at a corner of the stack, as near the base as practicable, and should be secured by a length of stranded galvanized-iron wire, passed round the stack. "Wire, Galvanized, Strand, 7/14" should normally be used, but "Wire, Galvanized, Strand, 4/8" should be used where atmospheric corrosion is such that the 7/14 wire would need frequent renewal. "Irons, Chimney" for providing a large bearing surface for the wire, should be fitted at the other corners of the stack.

9. Two types of chimney bracket are issued.
These are shown in Figs. 6 and 7. Both are described as "Brackets, No. 6". The difference between the two is that the bracket shown in Fig. 6 includes a "Swivel, Stay, 1/2in." for adjustment, whilst that shown in Fig. 7 has an adjusting eye-bolt and nut incorporated in the bracket. Both types are issued with two thimbles, for terminating the wire as described in D 3051 (when available).

FIG. 6
CHIMNEY FIXTURE - BRACKET No. 6
 

FIG. 7
CHIMNEY FIXTURE - BRACKET No. 6 (BULLER'S TYPE)
 

10. The threads and bearing surfaces of the swivel and the eye-bolt should be well coated with tallow, tar and pitch composition.

11. Eaves brackets
On account of lack of fixing facilities, or for other reasons, it may not be possible to lead-in direct from a chimney fixture by means of Cable, I.R.V. Core, T., 1-pr/12½. An intermediate fixture may be necessary, in the form of an eaves bracket "Bracket No. 14, or 15" as illustrated in Figs. 8 and 9. "Bracket No. 14" should usually be employed; "Bracket No. 15" should be employed only when the gutter overhangs the face of the wall to such an extent that a "Bracket No. 14" is inadmissible. On rare occasions it may be necessary to fit a "Bracket No. 15" between the slates or tiles and the roof boarding ; in such instances, care should be taken that workmen skilled in the removal of slates and tiles are employed.

12. Methods of leading-in which involve the use of eaves brackets are expensive, and should not be used without good reason (see E 3142).

13. When it is necessary to terminate two or more spurs at the same leading-in point, it is not permissible to fit two "Spindles No. 7" in the eyes of a "Bracket No. 2". Experience has shown that the close horizontal spacing of the wires (8in. or less, depending on the angle between wires and bracket) entails a high fault liability. A separate bracket should be provided for each pair of wires.

14. The attachment of additional spurs to existing house fixtures by means of terminal irons is forbidden.

15. Method of attaching fixtures to walls of buildings
To ensure, a firm fixture to brickwork or masonry, it will generally be necessary for the wall to be plugged, although occasions will arise where the consistency of the mortar is such that plugging will not be required. The cutting of rough-cast or decorative plaster work should be avoided as far as possible.

16. Brackets Nos. 2, 5 and 14
The brackets should be arranged so that the fixing holes coincide as far as possible with the mortar courses in the masonry; in the case of "Bracket No. 14," the vertical holes are spaced so as to enable this to be readily done. The positions of the nail-holes should be marked and a clean hole, about 1in. wide and at least 3in. deep, cut in the mortar by means of a "Chisel, Plugging, 9in."; wood plugs should be driven in until tightly wedged, and then cut off flush with the wall; finally, the bracket should be nailed in position by means of "Nails, Rosehead, 3in. or 4in." as required.

FIG. 8
EAVES BRACKET - BRACKET No. 14
 

FIG. 9
EAVES BRACKET - BRACKET No. 15

17. Spikes, Insulator
In brickwork, the position chosen should be alongside a brick which is set endwise to the face of the wall. This will ensure that only mortar, and not brickwork, need be cut prior to driving the spike. It is desirable, moreover, that the spike should be so placed with respect to the endwise brick that, under the pull of the wires, its tip will bear against this brick (see Fig. 1); if the tip of the spike bears against a brick set longitudinally, there is a certain tendency to lever the brick out of position.

18. Spikes should not be fixed within 12in. of the top course of brickwork; where the brickwork is new, an even greater distance should be allowed.

19. The slot for a spike should be cut by means of a "Chisel, Mortice".

20. Where the masonry is closely set, so that the resulting slot is only slightly wider than the spike itself, a good fixture can be obtained by means of a lead strip, used as packing, in lieu of a wood plug. The strip, which may be cut from 2in., 8lb. lead, or odd lengths of cable sheath - is trimmed approximately to the shape of the spike. One or more layers, as required, are placed in the slot, and the spike is then driven well home.

21. Wood plugs for walls should be cut from soft, straight-grained, non-resinous timber, of a type that does not split readily. For a fixture by means of a "Nail, Rosehead" between courses of brickwork, a hole roughly 1in. x 3/8in. should be taken out by a "Chisel, Plugging"; the exact width will depend on the width of the mortar course. The plug should be cut rather larger than the dimensions of the hole, and should be trimmed to a taper "on the skew" as shown in Fig. 10. To allow for possible voids in the brickwork, the plug should be cut about 5 to 6in. long; after being driven home, it should be cut off flush with the face of the wall. When the plug is in position it should be a tight fit in the hole in all directions. If the position of the plug is at the junction of horizontal and vertical courses of mortar, it may be necessary to modify the dimensions quoted above.

FIG. 10
TYPICAL WOOD PLUG FOR INSERTION IN HOLE,
APPROX. 1in. BY 3/8in., BETWEEN COURSES OF BRICKWORK
 

22. A plug for use with an insulator spike (Fig. 11) whilst filling the entire length and depth (1½in.) of the slot, should not fill the entire width, about 3/16 in. clearance space being left, into which the spike should be driven. Such a plug should also be cut on the skew.

FIG. 11
TYPICAL WOOD PLUG FOR FIXING,"SPIKE, INSULATOR" IN HOLE,
APPROX. 1½in. BY 3/8in., BETWEEN BRICKS

23. Method of attaching fixtures to timber
Brackets No. 10, and Brackets Nos. 2 and 5 when used on timber, should be attached by means of "Screws, for Wood, Iron No. 16 Countersunk Head, 1¾in.". Depending on the tension in the span and the quality of the timber, longer screws may occasionally have to be used.

24. Exceptional types of buildings
Occasionally, special types of construction are encountered; e.g. the irregular un-cemented masonry of the North of England, and the exterior lath-and-plaster construction found in the South. When attachment to the former is unavoidable, a careful choice of position will be necessary; the plugs used should be of generous size and should be specially out to suit each job. In the case of lath-and-plaster construction, a wood batten should be cut from stout timber, of a length sufficient to span two or three of the vertical studs to which the laths are attached. The studs should be located by "sounding" the wall and by careful boring with a bradawl; the batten should be secured thereto by means of 3½in. wood screws. The wall fixture should then be secured to the batten in the usual way.

25. Silencing of wires
Annoyance is sometimes caused to subscribers by the humming of wires attached to a house, under certain conditions. If a complaint is received, one of the three methods described below for preventing this effect should be adopted. The first method, which should be tried first, will generally be successful; if this fails, the second method should be tried. Persistent cases which do not yield to either of these should be dealt with by the third method.

26. The methods of silencing wires are:-

Method 1 - "Lead Strip,1/4 in." is spiralled round the wires at both ends of the spur for a length of about 10in., as shown in Fig. 12. About 30in. of lead strip is required at each termination.

Method 2 - The part of the termination which encircles the neck of the insulator is threaded through a short piece of lead sheath, stripped from a 1-wire or 1-pair lead-covered cable, which will produce a cushioning effect. between the wire and the insulator (see Fig. 13) The length of the lead sheath should be slightly greater than the circumference of the neck of the insulator. The wires should then be wrapped with lead strip as in method 1.

Method 3 - A short length of chain - say 6 to 12in. - is inserted in each wire, close to the house fixture. The chain should be purchased locally. To avoid sharp bends in the wire, the links should be of material not less than 1/4in. diameter. The chain is bound to the neck of the insulator by means of a double length of 40lb. cadmium-copper wire, made-off as shown in Fig. 14, the length of wire required being approximately 5ft. The line wire is made off through the link at the other end of the chain, and the tail extended direct into the insulator cavity.

FIG. 12
SILENCING BY MEANS OF LEAD STRIP, 1/4in.
 

FIG. 13
SILENCING BY MEANS OF LEAD SHEATH AND LEAD STRIP, 1/4in.
 

FIG. 14
SILENCING BY MEANS OF A SHORT LENGTH OF CHAIN

 


 

An exhibit of two types of Chimney Brackets

 

 

 

 
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