Permissible Tension of Drop Cable

The permissible tension of a drop cable depends on the cable type, fiber count, and installation method, with typical optical drop cables designed for aerial spans under 150 feet and rated tensile loads specified by the manufacturer.

Optical Drop Cables

For SST-Drop (Dielectric) optical cables, which are commonly used in fiber-to-the-home (FTTH) or fiber-to-the-business (FTTB) networks, the permissible tension is determined by the cable's rated tensile load. These cables are designed for short aerial spans, usually less than 150 feet, and are intended to bridge the distribution network to subscriber premises. Key factors affecting permissible tension include:

• Fiber count: Most drop cables have 2–12 fibers, with lower fiber counts generally allowing higher tensile loads per fiber .
• Environmental conditions: Wind, ice, and temperature variations can increase tension on aerial spans.
• Installation method: Direct-buried, conduit, or overlash installations have different tension limits. The cable should not exceed its rated tensile load during pulling or after installation .

Electrical Conductors and Pulling Tension

For electrical cables, the maximum permissible pulling tension is calculated based on the conductor material, size, and number of conductors. The general formula is:

• T = S × cmil × n (for n ≤ 3)
• T = S × cmil × n × 0.8 (for n > 3) Where T is the maximum tension in pounds, S is the allowable conductor stress (e.g., 0.008 lb/cmil for copper), cmil is the conductor cross-sectional area, and n is the number of conductors . Additional factors that limit tension include:
• Structural supports and sheave/pulley ratings
• Maximum sidewall bearing pressure of the cable
• Cable insulation and sheath limitations For example, a 1 AWG copper conductor with a single conductor can withstand a maximum pulling tension of 670 lbs, while larger conductors or multiple conductors have proportionally higher limits .

Practical Guidelines

• Always refer to the manufacturer's rated tensile load for the specific drop cable.
• Avoid exceeding the maximum sidewall bearing pressure during pulling, as this can damage the cable.
• Consider environmental loads such as wind, ice, and temperature changes when calculating permissible tension for aerial installations.
• Use proper pulling equipment (ropes, swivels, grips) and follow recommended installation practices to prevent overstressing the cable . By adhering to these guidelines, drop cables can be installed safely without compromising their structural integrity or optical/electrical performance.