Insulation displacement yields cost benefits

06/05/2002


I nsulation Displacement Connection (IDC) is a highly reliable connection technology. It has been used for many years in the telecommunications/electronics industry and has been making its way into industrial control and automation applications.

Passing stringent testing required of existing screw and spring technology terminal blocks, IDC has proven itself as a viable termination solution.

IMAGE controleng.com/archives/
2002/ctl0202.01/images/ctl0202bba1.jpg

Making an insulation displacement connection entails forcing a conductor through a space between two terminating blades making contact with metal.

IDC technology allows end-users to terminate wires without stripping or ferruling, thereby saving an average of 60% on installed costs while maintaining (or increasing) reliability and functionality.

Cost reductions are a continuous need in today's automation and control industry. In an effort to support requirements to reduce costs, suppliers must either reduce component costs (hard costs) or help reduce installation costs (soft costs). Although it is easier to reduce component costs, another way is through lower cost installation and maintenance.

The basic principle behind IDC technology is to mechanically force an unstripped stranded or solid conductor into a V-shaped metal tube. The opening on the V-shaped tube is smaller than the diameter of the conductor being inserted. Inserting the conductor creates an outward force on the terminating blades causing them to spread open exposing the bare copper to the terminating blades.

This outward force creates an equal or greater inward return force due to the tensile strength of the metal. These forces acting like a spring create a vibration resistant connection. In addition, as the connection is made, the terminating blades penetrate any existing film or oxide on the bare copper to form a gas-tight, corrosion-resistant connection.

DIN-rail mount IDC terminal blocks are required to pass the same UL, CSA, VDE, DIN, and IEC tests as screw and spring clamp technologies. IEC 60512-6 defines climatic tests, which include dry heat, high humidity with wide temperature changes, insulation resistance, voltage proof, contact resistance, mechanical operation, and visual examination.

Additional tests in IEC 61512-6 include corrosion, that is, testing the effects of a controlled, salt-laden atmosphere. Results are based on visual inspection for cracking, delamination, and pitting of metal surfaces. Another test looks at effects of rapid changes in temperature in the range from -55 °C to 55 °C (-67 to 133°F) for duration of 30 minutes with 5 cycles.

Vibration tests determine suitability when exposed to harmonic vibrations during transport or use. This applies vibration caused by rotating, pulsating, or oscillating forces (including vibration generated by machinery and seismic influences). IDC terminals are tested with the largest, as well as smallest, rated AWG for stranded and solid wire. First, a sinusoidal resonance test is completed, then a sinusoidal oscillation test is completed. Voltage drop is measured before, during, and after testing to ensure operability. In addition, contact separation is visually inspected during and after the testing.

Corrosive environment tests determine the effects of certain gases and humidity levels on IDC terminal blocks. One test is with SO2 (sulfur dioxide) in humidity levels of 100%. SO2 gas is used because it has a natural corrosive effect on nickel, steel, and zinc. Nickel and zinc are commonly used metal plating and steel is a commonly used base metal. The higher the humidity level, the more aggressive the gas becomes. Voltage drop is tested during and after the test. In addition, visual inspection of the contacts is made during and after the test for signs of pitting, cracking, and general deterioration.

IDC offers many benefits for control system wiring. It is well suited for signal connections, which typically make up the majority of connection points in a control system. Other ways DIN-rail mount IDC terminal blocks have added value include features such as built-in test points, marking capability at each termination point, and versions with electronic components.

-Dean Norton, product manager Wieland Electric dnorton@wielandinc.com




Jim Montague, news editor
jmontague@cahners.com

Control Engineering February 2002





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