Cat 6A Pull Tension and Bend-Radius Damage
A crew is pulling twelve Cat 6A cables into a 2 in (53 mm) EMT sleeve between two telecom rooms. The route is 110 m with four 90-degree bends. The tugger is set to 100 lbf (445 N) total, and the crew is pulling all twelve cables at once with a basket grip. No lubricant is used. The cable manufacturer lists a maximum pull tension of 25 lbf (111 N) per cable and a bend radius of 4 times the cable diameter during installation. The cable diameter is 0.30 in (7.6 mm). After the pull, three links fail return loss, and one cable has a wrinkled jacket about 1 m from a bend. The crew wants to certify the links because wire map and length pass, and the fail is only return loss.
1. Evaluate the conduit fill and the pull tension against the stated limits. Are they acceptable as described?
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2 in EMT has an internal diameter of about 2.067 in, area = pi x (1.0335)^2 = 3.36 in^2. At 40% fill, allowable = 1.34 in^2. Each Cat 6A cable diameter is 0.30 in, area = pi x (0.15)^2 = 0.0707 in^2. Twelve cables = 0.848 in^2, which is 25% fill, so fill is acceptable. Pull tension: 100 lbf total / 12 = 8.3 lbf per cable if the load is shared equally, below the 25 lbf per-cable limit. But a basket grip on a bundle does not guarantee equal sharing; one cable can take much more than the average, especially around four bends. The setup is not automatically acceptable because per-cable tension is not verified. Use a tension meter and a breakaway or swivel arrangement, or pull fewer cables at a time.
2. What do the wrinkled jacket and the return-loss failures indicate, and what should be done with the three failed links?
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A wrinkled jacket is evidence of mechanical damage: the cable was bent tighter than its minimum bend radius or pulled under excess tension. Cat 6A relies on precise pair geometry; deformation changes impedance and causes return-loss failures, especially at higher frequencies. Wire map and length only prove continuity and distance, not transmission performance. The three failed links cannot be certified. The damaged cable with the wrinkle should be replaced; the other two failed links should be inspected along the path, especially at bends and at the pull end, and re-terminated only if the cable itself is undamaged. If return loss persists after re-termination, replace the cable. Do not pass a link because the only failure is return loss.
3. What changes would you make for the re-pull, and what tests would you require before acceptance?
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Re-pull with a compatible lubricant, verify the minimum bend radius of 4 x 0.30 in = 1.2 in (30 mm) during installation at every sheave and guide, and use larger-radius guides or a different pathway at the four bends. Pull fewer cables at a time or use a tension-monitored tugger with a breakaway set below 25 lbf per cable; do not rely on total bundle tension. Keep the pull speed steady and avoid jerking. After installation, test every link as a Cat 6A permanent link with a calibrated tester, including insertion loss, return loss, NEXT/PSNEXT, and length; inspect and re-terminate any failures, then retest. Provide the full test reports and as-built documentation.