O.T.L. u



290 OVEEHEAD TRANSMISSION LINES

(6) Wrought-iron Masts.
The maximum working stress in iron structures is not to exceed 1,500 kg.
per square centimetre (21,500 lbs. per square inch).
The most unfavourable case is that occurring with a wind pressure of 125 kg.
per square metre of normal effective surface.
For cylindrical surfaces the effective surface area is to be taken as -7 times the
diameter multiplied by the length.
(c) Masts of Special Materials.
Masts of special material may be loaded up to one-third of the breaking stress
guaranteed by the makers. In the case of cast-iron structures the maximum
stress is, however, not to exceed 300 kg. per square centimetre (4,300 lbs. per
square inch).
(d) Erection of the Masts.
Poles and masts must be let into the ground to depths depending on their length
and on the nature of the soil (in average soil the depth is usually 1-5 to 2-5 metres).
The soil must be well punned (in soft soil special precautions may be necessary) and
the mast must be specially anchored or strutted at corner points.
In the case of road crossings with high-tension lines a mast must be placed
close to the road on each side and falling of the masts must be prevented as far
as possible either by their construction or by means of suitable stays or struts.
When both sides of a road are available for mast erection the east side should
preferably be chosen, because then the prevalent westerly storms will not be able
to blow down the masts across the roadway.
