Understanding Cableway Performance: New Insights From Torque Testing Sponsored

Hubbell Power Systems recently completed an extensive field and laboratory study to better understand why some customers were experiencing premature failures of cableway slots in concrete‑collar streetlight foundations. Although these foundations had been tested are rated for 10,000 ft‑lbs of torque, some field installations were reportedly failing below these values. The suspected culprit involved installation‑machine “crowd” forces—downward pressure applied during foundation installation—which could not be fully replicated in a traditional lab environment.

To address this, our team conducted a rigorous combined lab‑and‑field test series in Centralia, Missouri, using four different cableway geometries under multiple magnitudes of crowd. The findings provide new clarity on how cableway dimensions and installation forces interact to affect torsional capacity—and offer practical guidance for specifiers and installers.

Why We Tested: Replicating Real Installation Conditions

Earlier lab testing showed acceptable torque capacities, but lacked one real‑world factor: crowd force:

• Zero crowd tests conducted on the Hubbell Laboratories torque machine (calibrated to apply 25,000 ft-lbs of torque)
• Crowd applied field tests using a 2023 Terex digger derrick

A total of 36 samples were tested across four cableway sizes:

• 2.5" Wide × 12" Long
• 2.5" Wide × 18" Long
• 3.0" Wide × 12" Long
• 3.0" Wide × 18" Long

Each size was tested at 0 kip, 5.1 kip, and 9 kip of crowd. Three samples of each size were tested at each level of crowd force.

What We Found: Cableway Length Is the Dominant Factor

After analyzing the data—both directly and via a three‑way ANOVA—three variables emerged as statistically significant influencers of torque capacity:

1. Cableway Length (largest effect)
   Switching from a 12‑inch cableway to an 18‑inch cableway resulted in a 29.6% reduction in torque capacity. This was by far the most significant contributor to reduced strength.
2. Cableway Width
   Increasing width from 2.5 inches to 3 inches caused a 12.7% reduction in torque capacity.
3. Crowd Force
   Increasing crowd from 0 to 9 kips created an average 7.6% reduction in torque capacity.

These results confirm that all three variables—width, length, and installation crowd—measurably affect performance.

Visualizing the Trend: Torque vs. Crowd

The study plotted averaged torque values for each cableway size across the three crowd levels, producing linear trendlines with high correlation (R² values from 0.93 to 0.99). The takeaway is clear:

Higher crowd consistently reduces torque capacity across all cableway geometries, though geometry drives the majority of the reduction.

Practical Recommendations for Installers & Engineers

Based on the combined field and lab data, Hubbell recommends:

• Use the smallest applicable cableway length and width

Longer and wider cableways reduce the torsional capacity of 6" foundations.

• Minimize crowd force during installation

While crowd is necessary for proper installation, excessive downward pressure reduces torque capacity and increases the risk of deformation.

• Maintain awareness of combined effects

Cableway geometry and crowd interact—meaning the reductions stack.
For example, an 18" × 3" cableway under high crowd will experience both the reductions for the longer cableway as well as the wide cableway.

Hubbell is deeply committed to research, development, and rigorous testing as the foundation of everything we do. We continually invest in exploring new ideas, technologies, and methodologies to improve our products and services, ensuring they meet the highest standards of quality, performance, and reliability. We strive for continuous improvement, delivering innovative, dependable results to consistently meet customer needs and anticipate future challenges.