span and increase the sag. Assuming that the insulators swing out of the vertical
by an angle of, say, 35°, and that the length of the suspension is 4 feet, the reduc-
tion in span would amount to 2. X 2-35 = 4-7 feet (since an angle of 35° subtends
a chord of 2-35 at a radius of 4 feet).
The maximum length of wire in the span occurs at + 40° C. and is :

When the outer wires break and the temperature is + 40° C, this length of
wire wiU exist in a span of 130 — 4-7 = 125-3 feet.
Using the equation



L = a +



8(P
3a'



OVBEHEAD TEANSMISSION LINES 25

the value of the new sag is found to be :

d = Vl {L~a)a = V | (130-5 — 125-3) 125-3 = 15-6 feet.
o o

The height to the lowest cross-arm will therefore be made up as follows : —

Feet.
Minimum height above roadway . . . .23

Sag with outer wires broken . . . . .15-6

Length of insulator chain ...... 4



Height 42-6



Sag and Stress in Insulated Condxjctoes.
