Wire Pull Calculator — Tension, Jam Ratio & Bends
Free · works offline · no account · NEC 2023 tables
Know before you pull: estimated tension for the run, whether three conductors can jam in the elbow, and whether you’ve blown past 360° of bends since the last pull point.
Open the free calculator →How the math works
Straight-run tension is roughly weight per foot × length × coefficient of friction, multiplied up by an exponential factor at each bend. The jam ratio compares conduit internal diameter to conductor OD (D/d); the danger window is roughly 2.8–3.2, where three wires can wedge in a bend. And the NEC raceway articles cap total bends at 360° between pull points.
Worked example
Three conductors in rigid conduit, two 90° bends
- Total bend angle: 180° — within the 360° limit
- Check D/d: inside the 2.8–3.2 window → upsize one trade size
- Use lubricant when tension estimate approaches the conductor limit.
FAQ
- What is jam ratio?
- The ratio of conduit inner diameter to single-conductor outer diameter. Near 3.0, three same-size conductors can line up flat in a bend and wedge — upsizing the conduit or changing conductor count avoids it.
- How many bends can a run have?
- No more than 360 degrees total between pull points (boxes, conduit bodies) per the Chapter 3 raceway articles — four quarter bends and you’re done.
- Does lubricant change the math?
- Yes — it cuts the coefficient of friction roughly in half, which compounds through every bend multiplier on long pulls.