How much force (in lbs) is required to stretch a wire between poles. (sag = 3')?
Answer:
I found a sag table for 477 aluminum conductor (code named COSMOS). 150' of this conductor weighs 67 lbs. (pretty close to your 75 lbs)
At 90 F, 477 AL wire will have an initial sag of about 2' and a tension around 650 lbs. Allowing it to sag 3' will have substantially lower tension. Over time the wire will stretch a little bit. The final sag will be closer to 31" and have a tension closer to 500 lbs.
Keep in mind that the poles will need to support this tension without leaning. As the poles lean towards one another, the sag increases dramatically.
650 lbs x 10 ft = 6500 lb-ft of bending moment at the ground line.
It depends on the unit weight of the wire
P = w L^2 / 8 a = W L / 8a . . . where w = WL
P = 75 ( 150 ) / (8 x 3) = 468.75 lbs
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