Bell Telephone Laboratories - Wire-Wrap
October 1953 Radio-Electronics

October 1953 Radio-Electronics [Table of Contents] Wax nostalgic about and learn from the history of early electronics. See articles from Radio-Electronics, published 1930-1988. All copyrights hereby acknowledged.

After getting out of the U.S. Air Force in 1982, I was fortunate to get a job at the Oceanic Division of Westinghouse Electric Corporation in Annapolis, Maryland. Most of the guys who worked in the area with me were former electronics technicians from the armed forces. We spent most of our days (and often evenings) building small quantity specialty systems for the U.S. Navy. The facility was fairly small and was not set up for high volume production; that was the purview of the much larger operation based adjacent to the Baltimore / Washington International Airport (BWI), which built ground-based and airborne radar systems. Whilst there, I did a lot of wire-wrap assemblies that went into MIL-SPEC systems, primarily rack-mounted equipment in helicopters and aboard ships deploying towed sonar systems. As such, I received extensive training for performing soldering, wire-wrapping, electrical contact crimping, cable harness lashing, and other related skills - including how to unsolder and unwire-wrap. The initial certification course was two or three weeks long, with annual proficiency classes. During the class, we were given some background into wire-wrapping including how the wire-post interface is considered to be gas-tight, vibration-proof, and is very low resistance. Here is the 2012 version of MIL-STD-1130C, CONNECTIONS, ELECTRICAL, SOLDERLESS WRAPPED, where you can see what is required. The on-site Navy inspectors examined each connection using a magnifier. If the number of turns was too low, or the amount of slack between posts was too small, or there was a nick in a wire's insulation, or a post had too much surface contamination, or any of a host of other things was violated, we'd get a failure and had to re-work it. The boss was not happy when that occurred. This same ad ran in the October 1953 issue of Radio & Television News.

Bell Telephone Laboratories - A New Twist in Telephony

A solderless connection, enlarged 15 times. Connections are more uniform than soldered ones and only half as bulky.

For years the accepted way to connect wires to telephone apparatus was with solder. Now, Bell Laboratories engineers have discovered how to make connections faster and better - without solder.

Solder, they reasoned, wouldn't be needed if wire and terminal could be kept tightly pressed together. But, for economy, this had to be done with the wire alone - without complicating screws and springs.

They found the answer in using a properly dimensioned terminal with sharp edges ... whipping the wire around it under high tension. The terminal bites into the wire, locking it securely into position. Thereafter the squeezed edges maintain a contact pressure of at least 15,000 pounds per square inch - even under vibration that cracks soldered joints.

The new connections can be made in half the time - a big money-saver in the billion connections that Western Electric makes each year for the Bell System. It's another example of the way Bell Telephone Laboratories works continually to keep costs low.

Bell Telephone Laboratories

Improving Telephone Service for America Provides Careers for Creative men in Mechanical Engineering

Cross section of solderless connection. Note terminal biting into wire. In a six-turn connection there are at least 20 clean contact areas impervious to moisture and corrosive gases, offering current a low resistance path.

Power tool whips wire on terminal in fraction of a second. There is no heat which could damage miniature components ... no dropped solder or wire clippings to cause trouble later.

Posted November 10, 2020