Electrical Wire

Lore & Background

Modern wire wrapping technology was developed after WWII at Bell Laboratories as a means of making electrical connections in a new relay being designed for use in the Bell Telephone system. A design team headed by Arthur C. Keller developed the 'Keller Wrap Gun', and the entire wrap system was passed over to Western Electric for industrial application. After a 'make or buy' committee at Western Electric decided to have the hand tool manufactured by an outside vendor, Western Electric sent the tool contract out for bids. Keller Tool of Grand Haven, Michigan, a supplier of rotary hand tools to Western Electric, won the contract and made several design changes to make the tool easier to manufacture and to use. Keller began manufacturing the tools in 1953, and subsequently obtained a license from Western Electric allowing sale of the technology on the open market. The tool was marketed under its original name – since the name of the manufacturer was coincidentally the same as the name of the inventor.

In Their Own Story

IBM's first transistorized computers, introduced within the late 1950s, were built with the IBM Standard Modular System that used wire-wrapped backplanes. Wire-wrap was used by Apple Computer to make early prototypes of the original Macintosh computer (The Macintosh 128K). Automated wire-wrap machines, as manufactured by the Gardner Denver Company in the 1960s and 1970s, were capable of automatically routing, cutting, stripping and wrapping wires onto an electronic 'backplane' or 'circuit board'. The machines were driven by wiring instructions encoded onto punched cards, Mylar punched hole tape, and early micro computers.

Reader's Guide

A correctly made wire-wrap connection for 30 or 28 AWG wire is seven turns (fewer for larger wire) of bare wire with half to one and a half turns of insulated wire at the bottom for strain relief. The square hard-gold-plated post thus forms 28 redundant contacts. The silver-plated wire coating cold-welds to the gold. If corrosion occurs, it occurs on the outside of the wire, not on the gas-tight contact where oxygen cannot penetrate to form oxides. A correctly designed wire-wrap tool applies up to twenty tons of force per square inch on each joint. The sockets have square posts. The usual posts are 0.025 in (0.64 mm) square, 1 in (25.4 mm) high, and spaced at 0.1 in (2.54 mm) intervals. Premium posts are hard-drawn beryllium copper alloy plated with a 0.000025 in (630 nm) of gold to prevent corrosion. Less-expensive posts are bronze with tin plating. 30 gauge (~0.0509mm2) silver-plated soft copper wire is insulated with a fluorocarbon that does not emit dangerous gases when heated. The most common insulation is Kynar.

Did You Know?

• Wire wrap was invented to wire telephone crossbar switches before being adapted for electronic circuit boards.
• A correctly made wire-wrap connection uses seven turns of bare wire with half to one and a half turns of insulated wire for strain relief.
• The square post forms 28 redundant contacts, and the silver-plated wire coating cold-welds to the gold post.
• Automated wire-wrap machines from Gardner Denver in the 1960s and 1970s used punched cards or Mylar tape for instructions.
• Wire wrap was used for prototypes of the original Macintosh 128K computer.