OVERHEAD CONSTRUCTION
RING TYPE DISTRIBUTION POINTS


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P.O. ENGINEERING DEPT.
ENGINEERING INSTRUCTIONS
LINES
OVERHEAD
E 3130
Issue 3, 14.8.39

OVERHEAD DISTRIBUTION IN RESIDENTIAL AREAS
Open-wire Ring-type Pole-head D.P.s

1. General
The increasing opposition which is being experienced, from both public and private wayleave grantors, to the erection of poles for subscribers' distribution makes it extremely desirable that careful consideration be given to the appearance of overhead distribution lines in suburban areas.

2. Common types of construction types are:-

  1. The erection of "through" open-wire lines from a D.P. along a road, with services - open or drop-wire - to subscribers at intervals along the line.
     

  2. Armed distribution poles with no "through" wires, serving subscribers radially from arm positions or fittings attached to the ends of the arms.
     

  3. Cross-armed distribution poles, with or without "through" wires.
     

  4. Drop-wire distribution from pole-head distribution poles.

FIG. 1
SINGLE-RING TYPE - GENERAL VIEW

3. Type (a)
These are well adapted for the needs of an area with small development, but should not be used in suburban areas where reasonably good development is anticipated.

4. Type (b)
These can frequently lead to unsightly distribution poles, as well as to considerable technical inconvenience in arranging for the required spans to subscribers' premises. Arms were designed for through lines, and are ill-adapted for radial distribution.

5. Type (c)
These are unsightly in suburban streets, requires taller poles, and provides for a much greater capacity than is either necessary or desirable under modern conditions.

6. Type (d)
Whilst providing in many cases a sound and economic method of distribution, frequently leads to complaints due to the greater visibility of the covered wire in comparison with open wires. It should not be employed in situations where amenities are of primary importance.

7. Principles of distribution in residential areas
In order to meet present-day requirements and to render overhead distribution less liable to objection, the following general principles should be observed in designing local distribution plant in residential areas:-

  1. Where scanty development is anticipated, type (a), par. 2, should be employed.
     

  2. When the ultimate development is at least 7 circuits per 100 yards of road, distribution should be effected by ring-type distribution poles erected at suitable intervals along the streets. A spacing of 80 to 120 yards will meet the average case. Each pole being served by cable, wires should not be erected between poles.

8. Open-wire ring-type distribution pole
To meet the objections outlined in pars. 3 to 6, a type of distribution pole employing a "Pole Head, 15-way, Ring-type" has been developed, and should be used generally in good-class residential districts where the conditions of par. 7 (b) apply. Fig. 1 shows a typical case.

9. Normally, D.P.s should not carry more than 15 circuits but, in exceptional circumstances, the number may be increased to 20 circuits. One ring per D.P. will, therefore, generally suffice. It should be borne in mind, however, that only half the ring is available to each side of the road, and a second ring may therefore be required if the circuits cannot be accommodated in their appropriate positions on the single ring (see par. 16).

10. Height of pole
For the sake of appearance, the height of the poles should be the minimum which will provide the necessary clearance for the wires. The average case will be met by the use of 28' or 30' medium poles.

11. Fitting of pole-heads
When only one ring is to be provided, it should be fixed 15in. below the top of the pole. When two rings are required, the upper ring should be 15 in. below the top of the pole, and the lower ring 15in. below the upper. This provides for the rings to be lower than would be required by purely technical considerations, but it is desirable from the point of view of appearance.

12. The wrought-iron fixing strips should be adjusted, by bending, so that the ring is accurately centred on the pole. Coach screws should be used for fixing. The ring should be so fitted that the slot is uppermost and central with the terminal block.

13. Finials should always be fitted to poles which carry ring-type pole-heads.

14. Terminal blocks
The terminal block should be fitted so that its upper edge is flush with the top of the pole, the block facing squarely up or down the street. If it should be necessary to fit a second block on a pole, it should be fixed between the two rings, immediately below the first block (see Underground, K3102).

15. Spindles and insulators
For the sake of appearance, white "Insulators No. 16" should be used exclusively, together with "Spindles No. 7". Requisitions should be specially endorsed to show that white insulators are required.

16. Careful attention should be paid to the choice of spindle positions. Spindles should be fitted in holes as nearly as possible in radial alignment with the subscribers to be served. It is unnecessary to equip the rings initially with spare spindles and insulators; but, to ensure satisfactory clearance between adjacent circuits, such spindles as are fitted should be in positions which will leave suitable spaces for the circuits which may be expected subsequently.

17. Considerations of design have limited the space available for access to the terminal block, and it may be advantageous to defer the use of the two holes adjacent to the slot until the ring is reaching its full capacity.

18. In all cases, the plane of the "Spindle No. 7" should coincide with the direction of the pull of the wires. No attempt should be made to obtain clearance between neighbouring pairs by "splaying out" adjacent spindles. To facilitate the fitting of the spindles a "Spanner, Box, in. square" should be used.

19. Pole leads should be run tidily and in a systematic manner between the terminal block and the spindles. The leads should be run beside the P.C. cable from the terminal block to the slot in the ring, and then between the flanges of the channel to the spindles. On the pole, they should be secured by means of "Clips, Pole-lead, No. 2" (see G3904) or by "Lead Strip, 1in., 5lb." (see G3001); in the channel, by "Clips, Pole-lead, No. 3"; and to the spindles, by "Lead Strip, 1in.".

20. Since the pole-head has been introduced largely for the sake of improved appearance, it is important that the finished job should not be marred by untidy leads.

21. Pole steps should be fitted as described in C 3151.

22. Protection of cable on pole
To prevent damage to the P.C. cable by the wiremen's boots, a 15in, length of capping, known as "Capping, Steel, No. 3" should be fixed over the cable close to the top steps, as shown in Figs. 3 and 4. The capping should be secured by "Spikes, Dog" two of which should be fixed against the lower edge of the capping to prevent it slipping downwards. The outside of the capping should be painted black to tone with the colour of the pole.

FIG. 2
TWO-RING TYPE - GENERAL VIEW


 

FIG. 3
DETAIL OF SINGLE-RING TYPE
FIG. 4
DETAIL OF TWO-RING TYPE

23. Technical advantage of pole-head
Apart from improved appearance, the ring-type pole-head presents certain engineering advantages, viz:-

  1. The finished job is more rigid than arms, terminal irons, "Spindles, Nos. 7.A. and 10" etc.
     

  2. Subscribers' open-wire drops will always be run with the wires of the pair in vertical formation.
     

  3. The running of pole leads is simplified, and the leads are less liable to disturbance than those on arms.

24. Wayleave negotiations
In negotiating way-leaves it will occasionally be advantageous to indicate to wayleave grantors the type of D.P. which can be erected. For this purpose Fig. 1 of this Instruction has been published in suitable leaflet form as TE2096, which can be obtained on requisition from the Stores Dept. As only a limited quantity of the leaflet has been printed, copies should be obtained and held only by those officers directly concerned with way-leave negotiations.

 
 
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Last revised: March 13, 2022

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