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P.O. ENGINEERING DEPT
Issue 1, 19.8.36
Wiring on Buildings
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.
SINGLE CIRCUIT RUN ON SPINDLES No. 7, ON BRACKETS No. 5
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
Issue 1, 19.8.36
Running Subscribers' Spurs - House Fixtures
1. Choice of position
In selecting the positions for house fixtures, consideration should be given to
The clearances stipulated in B1301 should be observed.
The fixtures should be easy of access by workmen.
The fixtures should be as near as possible to the leading-in point, so
as to avoid the use of a long cable-lead.
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.
WALL FIXTURE - SPIKE, INSULATOR, No. 1 (Angle ABC not more than 60°)
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.
CORNER FIXTURE - BRACKET No. 2 (DOUBLE BRACKET) EMPLOYED TO OBTAIN CLEARANCE
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.
WALL FIXTURE - BRACKET No. 5 FLAT ON WALL (WIRES APPROXIMATELY AT RIGHT ANGLES
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).
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
CHIMNEY FIXTURE - BRACKET No. 6
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
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.
EAVES BRACKET - BRACKET No. 14
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.
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
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
SILENCING BY MEANS OF LEAD STRIP, 1/4in.
SILENCING BY MEANS OF LEAD SHEATH AND LEAD STRIP, 1/4in.
SILENCING BY MEANS OF A SHORT LENGTH OF CHAIN
An exhibit of two types of Chimney Brackets