Pulling cables — maximum pulling tension and minimum bend radius during installation

The cable cross-section & current-carrying capacity guide determines what cross-section a cable needs to carry a given operating current. This article covers a different kind of limit, one that has nothing to do with current-carrying capacity: the mechanical limits a cable must respect while being pulled (into conduit, cable tray or cable ladder) to prevent damage to the conductor, insulation or any armouring/screening.

Limit 1 — maximum pulling tension on the conductor

When a cable is pulled with a pulling eye attached directly to the conductor(s), a rule-of-thumb maximum tensile stress per unit cross-section applies, based on the conductor material's yield strength with a safety margin:

Copper: approximately 50 N/mm² of conductor cross-section.
Aluminium: approximately 30 N/mm² of conductor cross-section (lower than copper, due to aluminium's lower yield strength).

For a cable with, say, a 95 mm² copper conductor, this works out to a maximum pulling force of roughly 50 × 95 ≈ 4750 N. If the cable is not pulled via an eye on the conductor but via a pulling sock (mesh grip) around the entire cable jacket, a lower allowable pulling force applies, determined by the friction of the sock on the jacket rather than the tensile strength of the conductor itself — this value is given in the cable manufacturer's installation documentation and cannot be reliably approximated with a rule of thumb.

Note: besides the pulling tension itself, a limit also applies to the sidewall pressure the cable may experience in a bend during pulling — with excessive pulling tension combined with a tight bend, the cable can be locally crushed even if the tension itself stays within the straight-run limit.

Limit 2 — the minimum bend radius

Independent of the pulling tension, a minimum bend radius applies, expressed as a multiple of the cable's outer diameter (D), which must not be undercut during or after installation:

IEC 60502-1 uses baseline values of 15× D for single-core cables and 12× D for multi-core cables (both unarmoured).
Cables with metallic armouring, screening or sheathing (copper tape, steel wire armour, aluminium foil) typically require a larger bend radius than the unarmoured baseline, because every additional metallic layer undergoes irreversible plastic deformation if bent too tightly (wrinkling of a screen tape, fracture of armour wire).
Flexible cables (for example drag-chain cables) can allow a smaller bend radius (in the order of 4–5× D), specifically designed for repeated flexing.

Note: there is no universal bend-radius value for "a cable" — the exact minimum bend radius is manufacturer- and construction-specific and is given on the product datasheet; the IEC 60502-1 values are a baseline for common power cables, not an absolute lower bound for every cable type.

Why both limits must be checked independently

An installation can stay well within the maximum pulling tension and still damage the cable through an overly tight bend somewhere along the route (or conversely: a straight pulling run with no tight bends, but with excessive tension due to a route that is too long or too heavy). Both limits must therefore be checked separately against the actual route — checking only the pulling tension (for example with a tension meter during pulling) says nothing about whether a bend somewhere along the route is tighter than the minimum bend radius allows.

Practical relevance

When planning a cable route through conduit or cable tray with multiple bends, it must be verified in advance that every bend in the route complies with the minimum bend radius of the cable to be installed, and during pulling the tension (preferably measured, not estimated) must stay within the manufacturer's limit — especially on long routes with multiple bends, where friction effects accumulate.

Common mistakes

Applying a generic bend-radius rule of thumb to an armoured or screened cable without consulting the manufacturer specification — the IEC 60502-1 baseline values apply to unarmoured cables; armouring or screening typically requires a larger bend radius.
Treating pulling via a pulling sock the same as pulling via an eye on the conductor — the allowable pulling force is fundamentally different, because the sock transfers force via friction on the jacket instead of directly on the conductor.
Checking only the pulling tension and not assessing the bend radii along the route in advance — a cable can be locally damaged by an overly tight bend even when the measured pulling tension stays well within the allowed limit.