The supplier or user shall cause the supports for power lines to be so designed as to provide the following minimum factors of safety.
|
|
Based on type-tested breaking strength |
Based on calculated breaking strength |
Based on modulus rupture |
|
Steel lattice towers and cross-arms |
2.5 |
2.5 |
-- |
|
Solid drawn steel poles |
2.0 |
2.5 |
-- |
|
Welded steel poles and steel poles with swaged or telescopic joints |
2.2 |
2.5 |
-- |
|
Stay assemblies |
2.5 |
2.5 |
-- |
|
Reinforced concrete spun poles |
2.4 |
3.5 |
-- |
|
Mechanically vibrated reinforced concrete structures and components |
2.5 |
3.5 |
-- |
|
Other types of reinforced concrete structures and components |
2.75 |
3.75 |
-- |
|
Wooden members not continuously loaded |
3.5 |
- |
2.7 |
|
Wooden members subjected to continuos loading |
5.5 |
-- |
4.5 |
Provided that in calculating the factors of safety the supplier or user shall assume that -
a. there are no broken conductors;
b. every line conductor, cable or wire carried by the support is at a temperature of -5°C;
c. line conductors, together with the supports, are subjected to a wind pressure of 700 Pa; and
d. in the case of lattice structures the area for calculating the force due to wind pressure is 1.5 times the projected area of the members of one side and in the case of round, elliptical or hexagonal poles, conductors and wires the area is 0.6 times the projected area.