Every underground power cable installation succeeds or fails on one number: the pulling tension. Pull too little and the cable stalls or rubs in the duct; pull too much and the jacket is scuffed or the conductor is stretched beyond its elastic limit. This guide explains how to calculate cable pulling tension for underground cable pulling equipment and how to match the result to a real machine.
On a long duct route the tension builds up from three sources: the weight of the cable itself, friction against the duct wall, and any bends the route forces the cable around. A figure that is valid for a 200 m straight run can double or triple once curves and a rising route are added. Because the load grows exponentially with wrap angle, an un-calculated pull is the fastest way to scrap a cable.
On straight sections the tension rises as:
Tout = Tin + w · μ · L
where w is cable weight per meter, μ the friction coefficient (roughly 0.2–0.5 for lubricated cable in duct) and L the section length. Around each bend the capstan effect applies:
Tout = Tin · eμθ
with θ the wrap angle in radians. Summing the sections gives the total tension at the puller.
Take a 300 m duct with one 90° bend. Assuming a lubricated 0.3 coefficient, the bend alone multiplies tension by about 1.6. If the straight-run tension were 12 kN, the calculated total reaches roughly 19–20 kN. A machine is then selected with headroom above that figure. The Galaxy GS40 underground puller below illustrates the ratings a buyer should compare against the calculation:
| Parameter | Value | Why it matters |
|---|---|---|
| Max intermittent pull | 40 kN | Ceiling for short, high-load sections |
| Pull at max speed | 20 kN | Continuous tension when paying out at speed |
| Speed at max pull | 2.5 km/h | Safe laying rate near design tension |
| Diesel engine | 77 kW (103 hp) | Power reserve for friction rise |
| Bull-wheel diameter | 400 mm | Thicker rope, less bending stress |
| Max rope diameter | 16 mm | Matching pull rope to load |
| Total weight | 3000 kg | Stability and transport |
| Electrical system | 24 V | Standard control voltage |
The full 103 hp underground cable pulling equipment is built around exactly this rating set, and the wider Underground Cable Pulling Equipment range covers lighter cable conveyors that share the same clamping logic (for example a 3.5 kN conveyor rated for 25–180 mm cable).
It is set by the cable manufacturer, usually as a force per square millimetre of conductor area plus a jacket-friction limit. Never exceed the lower of the two.
Yes. Reducing the friction coefficient from 0.5 to 0.3 can cut the friction component by almost half, and its effect on bends is even larger.
Most installers apply 20–25% above the calculated tension to cover dimensional tolerances, cold cable stiffness and field misalignment.
Send us the cable diameter, weight per metre, route length, number of bends and duct friction data. With those inputs we can confirm the calculated tension and recommend the puller rating that covers it.
ผู้ติดต่อ: Mr. Marble Wu
โทร: 8613301534008
Thai
