Guy-Wire / Down-Guy Tension and Mast Download
The tension in a guy wire holding a mast, pole, or tower against a horizontal load, and the vertical compression it stacks onto the mast. A down-guy attached at height H_a and anchored a lead L away sits at theta = atan(H_a/L) above horizontal. To resist a horizontal top load H (wind, a conductor pull, a sign's wind area) the guy carries H / cos(theta) -- always MORE than the load, climbing steeply as the guy steepens -- and pulls DOWN on the mast by H x tan(theta) (the mast download the pole and footing must carry) and UP on the anchor by the same. A 500 lb load, 20 ft up, 20 ft out sits at 45 deg: 707 lb tension, 500 lb download. A guy at 63 deg more than triples the download -- why crews want long anchor leads. Single-guy statics only; the pole class, anchor capacity, guy grade, and the engineer / NESC / RUS govern.
Formula and source
theta = atan(attachment_height_ft / anchor_lead_ft); guy_tension_lb = horizontal_load_lb / cos(theta); mast_download_lb = horizontal_load_lb x tan(theta); anchor_uplift_lb = mast_download_lb.
Guy-wire / down-guy tension and mast download (engineering statics; for utility work NESC and RUS Bulletin 1724E), by name; the pole class, the anchor holding capacity, the guy grade, and the engineer of record govern.
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