Conduit fill, jam ratio, capstan pulling tension, and sidewall bearing pressure — all in one tool. Source-derived from NECA 101 (Standard for Installing Steel Conduits) and NEC 2023 Chapter 9 Table 1.
This calculator runs four independent checks on a planned cable pull. All formulas are source-derived from NECA 101 — Standard for Installing Steel Conduits, Couplings, and Connectors and NEC 2023 Chapter 9 Table 1. No backend call is made — every result is computed in your browser.
NEC Ch.9 T1 limits the cross-sectional area occupied by conductors inside a conduit. For three or more conductors the limit is 40 %; two conductors is 31 %; one conductor is 53 %. The calculator computes the total conductor area and divides by the inside cross-section of the selected conduit. A green flag means the fill is within code; orange between 35–40 %; red above 40 %.
Jam ratio is conduit inside diameter ÷ cable OD. For 3-conductor pulls, ratios between 2.8 and 3.2 increase the risk of one cable wedging between the others, jamming the pull. The tool flags this band in orange.
Each bend multiplies the tension by e^(μθ) where μ is the friction coefficient and θ is the bend angle in radians. Straight runs add μ × W × L where W is the weight per foot and L the segment length. The calculator accumulates tension start-to-finish through each bend in the sequence you enter.
SWP = Pulling Tension at bend ÷ Bend Radius (ft). Most cable manufacturers and NECA 101 limit SWP to 1,000 lb / ft of bend radius for non-leaded conductors. Exceeding this risks crushed insulation.
NEC Chapter 9 Table 1 (unchanged from prior cycles) limits conduit fill to 53 % for one conductor, 31 % for two, and 40 % for three or more conductors. The 40 % limit applies regardless of whether all three are current-carrying.
Use a higher-quality polyurethane-based pulling lubricant to bring μ down to 0.2 or below, add intermediate pull boxes to break the run into shorter segments, or specify lower friction conduit (PVC vs EMT). Splitting at a pull point that already has two 90° bends gives the largest tension reduction.
Yes. The capstan formula and fill calculation are conductor-material agnostic. Enter the actual OD and weight per foot from the manufacturer's datasheet — the calculator does the rest.
The NEC Ch.9 T1 fill limits apply only to power and lighting conductors. For Class 2/3 low-voltage and fiber, refer to NEC 725 and 770, and the specific manufacturer's maximum tension and bend radius — those can be 5–10× more restrictive than power cable.