Wire Pull Calculator
Pulling wire through conduit is one of the most physically demanding tasks in electrical work. The force required depends on the total weight of the wire, the length of the run, the number of bends, and the friction between the wire and the conduit walls. This calculator estimates the pulling tension so you can plan your pull and decide whether you need a mechanical puller.
The calculation uses the capstan equation, which models how friction at each bend multiplies the tension exponentially. Even a short run with several bends can require surprising force.
Wire Pulling Formulas
Straight Pull = Wire Weight × Run Length × Friction Coefficient
This is the force for a straight run with no bends
Total Pull = Straight Pull × e(μ × π/2 × N)
μ = friction coefficient, N = number of 90° bends
The exponential nature of the capstan equation means that bends are the dominant factor in pulling tension. A straight 200-foot run might need only 300 pounds of force, but adding three 90-degree bends can push that over 2,000 pounds. This is why the NEC limits conduit runs to 360 degrees of total bends between pull points.
Friction Coefficients
| Condition | Coefficient |
|---|---|
| No lubricant (dry pull) | 0.7 – 1.0 |
| Standard wire lubricant | 0.5 |
| High-quality lubricant | 0.2 – 0.35 |
Always use wire pulling lubricant on any significant run. It reduces friction, protects insulation, and can cut pulling tension in half or more.
How to Use This Calculator
- Enter wire weight — the combined weight per foot of all wires being pulled together. Look up wire weight in the manufacturer's data sheet or NEC Chapter 9.
- Enter run length — the total conduit run from pull point to pull point. You can enter feet, inches, or a combination.
- Enter number of 90-degree bends — count every 90-degree bend in the run. Two 45-degree bends equal one 90-degree bend.
- Set friction coefficient — 0.5 is the default for standard lubricant. Adjust higher for dry pulls or lower for premium lubricant.
- Read the results — Straight Pull Force shows the tension without bends. Estimated Total Pull includes the effect of bends. The Recommendation suggests what equipment to use.
Pull Force Guidelines
- Under 100 lbs: Easy pull by hand
- 100 – 300 lbs: Moderate pull, manageable with a small team
- 300 – 600 lbs: Use a pulling grip and extra hands
- Over 600 lbs: Consider a mechanical wire puller
Frequently Asked Questions
How do bends in conduit affect wire pulling tension?
Each bend in a conduit run multiplies the pulling tension exponentially. The capstan equation shows that the force after a bend equals the force before the bend multiplied by e raised to the power of the friction coefficient times the bend angle in radians. A single 90-degree bend with a friction coefficient of 0.5 multiplies the pulling force by about 2.2 times. Two bends multiply it by about 4.8 times. This is why the NEC limits conduit runs to 360 degrees of total bends between pull points.
What friction coefficient should I use for wire pulling?
A friction coefficient of 0.5 is typical for wire with standard pulling lubricant. Without lubricant, friction can be 0.7 or higher. With high-quality lubricant applied generously, you can achieve values as low as 0.2 to 0.35. Always use wire pulling lubricant on any significant run to reduce tension and prevent damage to the wire insulation.
When should I use a mechanical wire puller?
Consider using a mechanical wire puller when the estimated pulling tension exceeds 600 pounds. For pulls between 300 and 600 pounds, use a pulling grip and a team of helpers. Under 300 pounds, a moderate pull by hand is usually manageable. Under 100 pounds, the pull is easy. These thresholds depend on your crew and the specific wire being pulled. Always stay within the maximum pulling tension rating for your wire to avoid stretching the conductor or damaging the insulation.