Do you know what that color coating on the outside of a wire is called? It is called insulation. And did you know that the day that wire is developed, the insulation of the wire starts to age and deteriorate? Unfortunately, it is true. Wire insulation is not like a fine wine; it does not improve with age. And with age, what about a wire’s “electrical” strength? Over time its performance deteriorates and its ability to isolate the conductor is decreased. Subjecting the wire to harsh environments and temperature-extremes accelerates insulation degradation even further. Damage to a wire’s insulation during manufacturing of electrical wiring harnesses, such as a nick by a wire cutter, can also lower the insulation’s integrity. That’s why it is imperative in the Aerospace and Defense Industry that all wiring harnesses be thoroughly tested for insulation resistance, among other things.
The simplest of tests used to detect breakdowns in wire insulation is an “insulation resistance” test or “IR” test. Although the IR test was developed in the early 1900s we still use it today. Here at InterConnect Wiring most of our wiring harnesses and panels are installed in military aircraft. A hazardous situation can exist if a wire insulation failure adversely affects equipment or causes personal injury – especially while in the air. Therefore, we understand how extremely important it is for us to detect any insulation deterioration quickly in our electrical wiring products during the manufacturing process and take preventive measures. During an IR test, the test equipment applies a (non-destructive) high direct current (DC) voltage, usually 500 to 1500 VDC, between a conductor and one or several other conductors for a specific time. Since we are testing for wire insulation integrity we want little or no current to flow between the conductors. Thus, a high resistance value is expected – typically 35 to 100 Megohms.
Every electrical test we run on our products includes IR tests. We are very aware that wire insulation breakdown can exist even though it may not be visible to the naked eye. We have made advancements over the years in testing our products to make sure that our wires are “electrically” strong. Insulation Resistance (IR) testing is not only important, but it is also required for all flight-worthy military and commercial aircraft electrical wiring harnesses and cable assemblies.
InterConnect Wiring and our top-notch testing group were featured in the magazine, Aerospace Testing International. Refer to page 91 to read about how we improved our testing efficiency significantly when we supported the rewire of multiple F-15 aircraft for the USAF.