Wire Combination Unilay-Stranded Copper Conductors for Subsequent Insulation

B787/B787M-04: Standard Specification for Wire Combination Unilay-Stranded Copper Conductors for Subsequent Insulation

For engineers and designers working with electrical conductors destined for insulation, understanding the precise construction and material properties is paramount. ASTM B787/B787M-04 provides an essential framework for specifying and manufacturing wire combination unilay-stranded copper conductors. This authoritative standard ensures the reliability and performance of these conductors in a wide array of demanding applications.

What is B787/B787M-04?

ASTM B787/B787M-04 is a comprehensive standard specification detailing the requirements for bare copper conductors formed using a specific "combination unilay" stranding method. Developed by ASTM International, its primary purpose is to define the construction, material properties, and testing criteria for these conductors, ensuring they are suitable for subsequent application of electrical insulation. This standard focuses on conductors designed for a specific purpose, moving beyond general conductor classifications.

Scope & Purpose

This standard governs the manufacturing and material specifications for bare copper conductors constructed with a central core wire surrounded by two layers of helically laid wires. It specifically covers conductors made from round copper wires, which can be uncoated or coated with tin or lead alloy. The unique "combination unilay" construction aims to achieve an outer diameter equivalent to compressed-stranded conductors. The standard does not cover insulated conductors themselves, nor does it address general conductor classifications like Class AA, A, B, or C, as its focus is on the bare conductor prepared for insulation.

Who Must Comply?

• • Primary Audience: Electrical Engineers, Materials Engineers, Wire and Cable Manufacturers, Quality Control Inspectors, and Product Designers involved in the specification and production of electrical conductors.
• • Industries Affected: Electrical Equipment Manufacturing, Power Transmission and Distribution, Telecommunications, Automotive, Aerospace, and any sector utilizing custom-stranded copper conductors for insulated wiring.
• • Compliance Nature: Typically voluntary, but often becomes a de facto requirement when specified in purchasing contracts, design specifications, or project requirements.
• • Enforcement: Compliance is generally enforced through contractual agreements, quality assurance programs of manufacturers, and inspection by purchasers or independent testing agencies.

Key Requirements Overview

• • Conductor Construction: The standard mandates a specific 19-wire combination unilay stranding pattern, featuring a central core wire and two subsequent layers of helically laid wires with defined diameter relationships.
• • Material Specifications: Professionals must ensure that the individual copper wires used conform to relevant ASTM specifications for uncoated or coated (tin or lead alloy) soft, medium-hard, or hard-drawn copper wire, depending on the application.
• • Lay Direction and Length: The standard specifies requirements for the direction and length of lay for each stranding layer to ensure dimensional stability and electrical performance.
• • Physical and Electrical Properties: Key provisions include requirements for the physical and electrical properties of the constituent wires, with allowances for minor variations when tested after stranding.
• • Testing Criteria: The standard outlines the methods and criteria for physical and electrical testing of the stranded conductors to verify conformance to specified requirements.

Related Standards & References

ASTM B787/B787M-04 is often used in