Worked Example: Cable Pulling Feasibility for a 185mm² Feeder at an Open-Pit Mine

At a copper-gold mining operation, electrical engineers regularly face demanding cable installation scenarios: pulling heavy power feeders through long cable duct routes across the process plant, with tight bend radii around structural steelwork, elevation changes between levels, and limited access during shutdowns.

A typical scenario involves installing a 185mm² Cu 3C+E XLPE feeder cable from the pit-rim switchroom to supply a primary crusher motor. The cable route passes through a 150m duct run with a 25m elevation change (approximately 10° incline on the ramp section) and two mandatory 90° bends where the route changes direction around haul road crossings and plant steelwork.

Getting this wrong means a cable stuck mid-pull, a wrecked cable jacket from excessive sidewall bearing pressure, or worse — a cable that passes installation but fails in service due to conductor damage from overpulling. Each failed pull attempt costs the operation approximately A$15,000 in labour, cable, and production downtime.

This worked example demonstrates how ECalPro’s Cable Pulling Calculator models the physics of this installation and determines feasibility before the cable drum even reaches site.

Route Segments (Pull Direction A: Switchroom → Crusher)

The cable weight force per unit length is the foundation of all tension calculations:

w = m × g = 8.49 × 9.81 = 83.29 N/m — (Eq. 1)

For a single 185mm² 3C+E XLPE cable at 8.49 kg/m, the gravitational force is 83.29 newtons per metre of cable. This force drives both the friction component (horizontal) and the gravity component (inclined sections).

The maximum pulling tension that the conductor can withstand without permanent deformation:

T_max = k × A = 70 × 185 = 12,950 N (12.95 kN) — (Eq. 2)

For copper conductors, k = 70 N/mm² per AEIC CS8 and NEC Section 300.17. This is the absolute ceiling — exceeding this tension risks stretching the conductor, reducing its cross-sectional area, and increasing resistance permanently.

Before calculating tension, verify the cable physically fits in the duct:

Fill% = (π × (49/2)²) / (π × (110/2)²) × 100 = 1,885.7 / 9,503.3 × 100 = 19.8% — (Eq. 3)

For a single cable, the NEC Chapter 9, Table 1 limit is 53%. Our fill of 19.8% is well within limits. ✓ PASS

Now we calculate the cumulative tension through each segment, starting from T_in = 0 N at the switchroom:

Segment 1: Straight 60m at 0°

T₁ = 0 + 83.29 × 60 × 0.30 × cos(0°) + 83.29 × 60 × sin(0°)

T₁ = 0 + 1,499.2 + 0 = 1,499 N — (Eq. 4)

Segment 2: Bend 90°, r = 0.8m

Applying the capstan equation:

T₂ = T₁ × e^{(μ × θ)} = 1,499 × e^{(0.30 × π/2)} = 1,499 × 1.602 = 2,402 N — (Eq. 5)

SWBP at this bend: 2,402 / 0.8 = 3,003 N/m (within 5,000 N/m limit) ✓

Segment 3: Straight 50m at 10° (ramp to crusher level)

T₃ = 2,402 + 83.29 × 50 × 0.30 × cos(10°) + 83.29 × 50 × sin(10°)

T₃ = 2,402 + 1,232.1 + 723.1 = 4,357 N — (Eq. 6)

Note the 10° incline adds 723 N from gravity — a 16% increase over a horizontal run of the same length.

Segment 4: Bend 90°, r = 0.8m

T₄ = 4,357 × e^{(0.30 × π/2)} = 4,357 × 1.602 = 6,980 N — (Eq. 7)

SWBP at this bend: 6,980 / 0.8 = 8,725 N/m

✗ SWBP EXCEEDS 5,000 N/m LIMIT! This is the critical finding.

Segment 5: Straight 40m at 0°

T₅ = 6,980 + 83.29 × 40 × 0.30 = 6,980 + 999.5 = 7,980 N — (Eq. 8)

Verdict: FAIL — The pulling tension is acceptable, but SWBP at Bend 4 exceeds the IEEE 1185 limit by 75%. The cable jacket will likely sustain damage during installation.

The ECalPro calculator identifies the problem before the pull attempt. Here are the engineering solutions, ordered by effectiveness:

1. Increase bend radius to 1.5m: SWBP = 6,980/1.5 = 4,653 N/m — within limit. This requires rerouting the duct with a wider sweep at the direction change, which is feasible if identified during design.
2. Use cable lubricant: Reducing μ from 0.30 to 0.15 (lubricated HDPE) cuts tension at Bend 4 from 6,980 N to approximately 4,100 N — SWBP = 5,125 N/m. Marginal but potentially acceptable.
3. Pull from the opposite direction: Direction B (crusher end → switchroom) encounters the steep incline as a downhill run, reducing gravity-assisted tension buildup before the critical bends.
4. Install an intermediate pull point: Break the route into two pulls with a junction box at the midpoint, ensuring each pull segment stays within SWBP limits.

In practice, the combination of cable lubricant and pulling from the crusher end (Direction B) proved successful, with measured SWBP below 4,000 N/m throughout the route.

ECalPro’s Cable Pulling Calculator performs this entire analysis in seconds, including bidirectional comparison and segment-by-segment tension profiling. Model your actual route, cable, and conduit parameters to verify feasibility before committing to installation.

The calculator supports single-core and multi-core cables from 1.5mm² to 400mm², with reference data from Nexans, Prysmian, and Olex catalogues. Override cable OD and weight with your actual datasheet values for maximum accuracy.