The cable pull is where design meets reality — and where mistakes cost the most. A conductor damaged during installation may not fail for months or years, eventually arcing and faulting inside a wall, underground duct, or above a ceiling where access is impossible. Cable pulling calculations predict the maximum tension and sidewall pressure at every point along the route, ensuring that the installation does not exceed the conductor's mechanical limits. These calculations are especially critical for long runs, multiple bends, and large conductors where pulling forces can reach thousands of pounds.

Maximum allowable pulling tension depends on conductor material and cross-sectional area. For copper conductors: maximum tension (lbs) = 0.008 × cmil area per conductor. For aluminum: 0.006 × cmil area. A single 500 kcmil copper conductor can withstand: 0.008 × 500,000 = 4,000 lbs. When pulling multiple conductors simultaneously with a basket grip, the tension distributes unevenly — the outer cables bear more load. For three conductors, multiply the single-cable limit by 0.6 (cradle configuration) or by the number of cables for pulling eye attachments where each cable has its own mechanical connection.

Sidewall bearing pressure (SWBP) at conduit bends is frequently the controlling limit — not the straight-pull tension. SWBP = T / R, where T is the tension at the bend (in pounds) and R is the inside bend radius (in feet). Maximum SWBP limits: 300 lb/ft for standard jacketed cables, 500 lb/ft for lead-sheathed cables, 1,000 lb/ft for interlocked armor cables. A 90° bend with a 24-inch radius carrying 6,000 lbs of tension produces: 6,000 / 2.0 = 3,000 lb/ft — far exceeding cable limits. This is why large conduit bends use sweep elbows (36-inch or 48-inch radius) rather than standard preformed 90° bends.

Each bend in a conduit run multiplies the pulling tension by a factor that depends on the coefficient of friction and the bend angle. For a 90° bend: T_out = T_in × e^(μ × π/2). With a friction coefficient of 0.35 (PVC without lubricant), the multiplier is e^(0.35 × 1.571) = 1.73 — each 90° bend increases tension by 73%. Three 90° bends compound: 1.73³ = 5.18 — the pulling tension at the end is over 5 times the starting tension. Using lubricant (μ = 0.15) reduces the multiplier to 1.27, and three bends compound to only 2.05×. This is why NEC limits conduit runs to 360° of bends between pull points.

Cable pulling lubricant selection is not trivial. The lubricant must be compatible with the cable jacket material (XLPE, PVC, CPE, Hypalon), must not degrade the conductor insulation over the cable's lifetime, and must provide adequate friction reduction at the expected temperature range. Water-based lubricants (most common for general-purpose pulls) are compatible with most jacket types but lose effectiveness at low temperatures. Wax-based lubricants perform better in cold weather but may not be compatible with certain XLPE insulations. The lubricant must be UL-listed or manufacturer-approved for the specific cable type.

For medium-voltage cables (5 kV – 35 kV), minimum bending radius requirements are significantly more restrictive than for low-voltage conductors. NEC 300.34 and cable manufacturer specifications typically require minimum bend radii of 12× the cable's overall diameter for shielded single-conductor cables and 7× for multiconductor cables. Violating the minimum bend radius can damage the conductor shield, creating a point of partial discharge that progressively erodes the insulation — a failure mechanism that may take months to develop into a complete fault.