MachineCalcs

Conduit Pull Tension Calculator

Screen wire or cable pulling tension through a conduit run from cable weight, straight length, friction coefficient, total bend angle, bend radius and manufacturer-entered pull limits.

Electrical 8 inputs 8 results

Calculator

Inputs

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Initial tension before the screened straight run and bend group. Use 0 if the setup starts slack, or an estimated feeder tension if already under load.
lbf
Installed cable or conductor bundle weight per route length. Include all pulled conductors in the bundle.
lb/ft
Equivalent straight conduit length before the bend group in this screening model.
ft
Sliding friction coefficient for cable jacket, conduit material, lubricant and field condition.
Sum of bend angles in the pull section. Two 90 degree bends equals 180 degrees.
°
Use the smallest effective radius where the cable bears on a bend.
in
Maximum allowed pulling tension from cable manufacturer data, pulling eye rating or project rule.
lbf
Maximum allowed sidewall bearing pressure at bends, usually provided by cable manufacturer guidance.
lb/ft

Results

Default result
Edit inputs
Final pull tension(T)
112.6lbf
Pass

Compare with the cable or pulling-eye tension limit.

Also computed

Sidewall pressure(SWP)Pass225.2lb/ft

Calculated from peak pull tension divided by the smallest bend radius.

Pull tension utilization(UT)Pass22.52%

Sidewall utilization(USWP)Pass75.07%

Straight-run friction force(Fstraight)17.5lbf

Fstraight = mu x cable weight x straight length.

Bend multiplier(Mbend)3.003x

Capstan multiplier e^(mu x theta) with theta = 3.142 rad.

Max straight length before limit(Lmax)171.2ft

sidewall pressure controls first with the entered cable limits.

Pull section friction screen start pull final tension bend capstan multiplier 23% pull limit 75% sidewall verify cable limits
Method notes 3 notes
  • Straight pull model: T_straight = T0 + mu x w x L.
  • Bend model: T_out = T_in x e^(mu x theta), where theta is total bend angle in radians.
  • This is a screening model. Real pull tension depends on route order, lubricant, cable jacket, conduit material, feed setup, pulling equipment, minimum bend radius, jamming and manufacturer limits.

Conduit pull tension starts with straight-run friction, Tstraight = T0 + mu*w*L, then applies bend friction with the capstan relation Tout = Tin*e^(mu*theta). Here w is cable weight per length, L is straight pull length and theta is total bend angle in radians. This calculator also checks sidewall pressure, SWP = T/R, against your entered cable limit.

Continue workflow

All Electrical
Next 1 Lay out conduit offset Lay out the offset bends and bend budget before summing the pull-section bend angle. Next 2 Check conduit fill Check raceway fill before trusting a route that also needs a pull-tension screen. Next 3 Check box fill Check box or junction volume where the same conductors terminate, splice or pass through. Chart Use reference data Transformer kVA chart

How to use this calculator

  1. Enter cable weight and route length. Use the total conductor or cable-bundle weight per foot or metre, then enter the equivalent straight pull length.
  2. Set the friction coefficient. Use manufacturer or project guidance for the jacket, conduit material, lubricant and field condition.
  3. Sum the bends. Add the bend angles in the pull section. Two 90 degree bends enter as 180 degrees.
  4. Enter the smallest bend radius. Use the smallest effective radius where the cable bears on the raceway or fitting.
  5. Compare with cable limits. Enter the manufacturer pulling-tension and sidewall-pressure limits, then check utilization and max straight length.

How it works

The straight-run portion treats cable weight as a line load and applies sliding friction: Tstraight = T0 + mu x w x L where T0 is starting tension, mu is friction coefficient, w is cable weight per length and L is straight pull length.

Bends use the capstan relation: Tout = Tin x e^(mu x theta) with theta in radians. The calculator treats the entered bend total as an equivalent bend group after the straight run, then screens sidewall pressure: SWP = T / R using the smallest bend radius you enter.

Pair this page with the conduit fill calculator for raceway area, the conduit bend offset calculator for route geometry, the ampacity derating calculator for current-carrying conductor adjustment and the voltage drop calculator for long-run electrical loss.

Worked example

Verified against the live calculator

Suppose a pull starts at 20 lbf, the cable bundle weighs 0.5 lb/ft, the straight pull is 100 ft, friction is 0.35, and the run includes two 90 deg bends. Straight friction adds 0.35 x 0.5 x 100 = 17.5 lbf, so tension before the bends is 37.5 lbf. The bend multiplier is e^(0.35 x pi) = 3.00, giving a final pull tension near 112.6 lbf. With a 6 in bend radius, sidewall pressure is about 225 lb/ft.

Reference data

This page intentionally asks for the project-specific cable limits instead of publishing a generic cable table. Use the cable manufacturer and field pull plan for the values below.

Conduit pull tension input sources.
Entered value Where it should come from
Cable weight per length Cable datasheet, takeoff, or total conductor bundle estimate.
Friction coefficient Cable jacket, conduit material, lubricant and field-condition guidance.
Allowable pull tension Cable manufacturer maximum, pulling eye rating or project cable schedule.
Allowable sidewall pressure Cable manufacturer sidewall bearing limit for the actual cable construction.
Bend radius Smallest effective conduit, sweep, sheave or fitting radius in the pull section.

Source: User-entered manufacturer and project values; verify against the actual cable, raceway and pulling method.

Frequently asked questions

How do you calculate conduit pulling tension?

For a straight run, this screen adds friction as T = T0 + mu x w x L. For bends, it applies the capstan multiplier T_out = T_in x e^(mu x theta), where theta is the bend angle in radians.

What is sidewall pressure in a cable pull?

Sidewall pressure is the bearing pressure where the cable rides around a bend. This calculator screens it as pull tension divided by bend radius, then compares it with the allowable sidewall pressure you enter.

What friction coefficient should I use for wire pulling?

Use project or manufacturer guidance when available. The correct friction factor depends on cable jacket, raceway material, lubricant, cleanliness, temperature and field setup. The default is only a screening placeholder.

Does this replace a cable pulling plan?

No. It is a route-friction screen. Final pulls need the cable manufacturer maximum pulling tension, sidewall-pressure limit, minimum bend radius, pulling equipment, lubricant, conduit condition, pull boxes and adopted code review.

Method & assumptions

  • Uses a straight-run friction screen plus a capstan bend multiplier; it does not model every bend in field order.
  • Uses user-entered cable weight, friction coefficient, maximum pull tension and sidewall pressure limit.
  • Sidewall pressure is screened from peak tension divided by smallest bend radius.
  • Does not check conductor ampacity, conduit fill, box fill, overcurrent protection, cable jamming, reel setup, lubricant selection, pulling-eye hardware or equipment ratings.
  • Final work needs the cable manufacturer limits, adopted code edition, local amendments, site conditions and qualified electrical review.
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