In the early days of connectors (1940s) wires were generally soldered. Then came crimp contacts that created gas-tight connections between wires and contacts by compressing the wire in a U shaped portion of the contact. Crimping required stripping wire and placing it into a crimp machine one by one. Crimping has proven to be an extremely reliable wire termination method and remains the dominant form of termination of individual wires even today.
In 1959, a significant change in the industry was born when a pair of inventors patented “Insulation Displacement Termination (IDT or IDC)” of wires to contacts, stimulating rapid innovation within the connector industry to take advantage of the cost and labor savings offered by this technology. In tracking back the origin of the invention, I came upon US patent # 3012219 from Edward Leach and Evert Levin, from Minnesota Mining and Manufacturing, now known as 3M.
The description of the technology in the patent is refreshingly clear and simple, like the concept itself. The quoted text is from the patent, typos and all:
“These wire-connectors are easily and rapidly applied to bare or insulated wires, forming low-resistance connec- The connection is permanent and is not loosened by repeated mechanical stresses, temperature or pressure changes, exposed to moisture, or passage of electrical current; and the initial low resistance is maintained. No preliminary stripping of insulation is required. The connector penetrates and displaces the plastic, paper or other insulating covering during application, making and maintaining a positive metal-to-metal juncture. Twisting and soldering operations are avoided. No special tools are required, the connector being applied to most wire-sizes by means of common pliers or side-cutters. In a preferred form, the connector provides its own insulating covering, and positively indicates the completion of the connection. Although the connection is permanent under all operating conditions, the connector may if necessary be removed and re-applied. The connector is further characterized by simplicity of construction and manufacture.”
I truly wish patent lawyers today could embrace simple descriptions like this.
This concept involved a forked contact with a slot to accept an insulated wire. As the wire is pushed into the slot, the insulation is displaced and the edges of the metal slot make contact with the wire. The simple slot in the wide, flat contact creates a strong spring that squeezes the wire with enough force to create a gas-tight, highly reliable joint. It is important to choose the right IDT contact type for the wire being terminated. The slot is custom for the wire gauge and also may be different for solid and stranded wires. Care must also be taken with insulation displacement connectors to create a strain relief so that the wire cannot move after the termination has been made. This is generally done by designing the plastic so the wire is trapped, with no movement at the contact point. Here are examples of folding the wire back through a slot or by having plastic features that lock onto the insulation around conductors, preventing movement.
The breakthrough invention enabled termination of wires or cables in the field without tools, or with very simple tools that provide compression pushing the wires into the slots and often locking the top of the housing in place, permanently protecting the joint. One of the initial applications of this connector style was in telecommunication systems, first displacing the screw taps found in many wall plates and inside the phones themselves.
An even more important application of the technology is in the 50-pin connectors that have been the heart of the telecommunication network for decades. These cables are field terminated by an operator with a simple machine that fans out wires to be IDT terminated to side piercing contacts. Hundreds of these connectors can be found in central offices connecting to wire bundles from the field. However, this technology is being displaced over time by VOIP phones that most of us use today.
Flat cables were used in early computing systems to connect storage drives. By placing multiple connectors onto a flat cable, it was possible to create bussed communication channels. The flat cables are easy to terminate, easy to route (at least in two directions,) and inexpensive to use. These flat cables remain stalwarts in many applications across the many industries.
Insulation in the appliance business has taken a slightly different approach. Fully automated harness machines were able to auto feed the connectors and the cables, creating a complex assembly in a matter of seconds. You will find these connectors all over the appliances in your kitchen, laundry room and basement.
IDT is one of the technologies that has increased your quality of life by enabling cost effective wiring harnesses that are found all around you in telecom, computing equipment, point of sale, gas pumps, ATMs, etc. Please give a nod to the innovative inventors, Edward Leach and Evert Levin, for their contribution to this quality of life the next time you use one of these systems.