Wiring Harness News WHN Sept-Oct 2020 WHN Sep-Oct 2020 - Page 47

INDUSTRIAL INFO-TAINMENT Wiring Harness News SEPTEMBER/OCTOBER 2020 47 variants (respectively) of the smooth surface PTFE-Polyimide construction with silverplated extra high strength copper alloy conductor. Table 1 shows the list of tests that are required for both construction types and have the same requirements. With the exception of two tests (dynamic cut through and abrasion resistance), both the light weight wire and normal weight wire share a common test basis. This makes sense that the chemical and thermal testing requirements are the same for both of the two wire constructions; the insulating materials are the same and so is the conductor. However, it is important to note that while the performance requirements are the same, this does not mean that they are the same. For example, 5 mils of insulation will have lower dielectric strength than the same insulation if the thickness is doubled to 10 mils. Slowly increasing the voltage until the insulation is breached would undoubtedly find a lower threshold voltage for the 5mil wall thickness. This also gives an insight into the performance of normal weight constructions. Even with a reduction of 20 – 30% of insulation thickness due to a physical trauma like abrasion, notch, or crushing, a normal weight construction would still be able to meet or exceed the performance requirements (given that a light weight construction is already thinner, made of the same materials, and has the same performance level). • Flex Life • Insulation Tensile Strength • Notch Propagation • Stiffness and Springback • Circumferential Insulation Elongation This is not to say that the performance differences are significant in every application, but there are applications where these factors should be addressed before selecting a light or normal weight wire construction. Restriction of Light Weight With the differences identified, next comes the application differences. The wiring bible of AS50881 is a starting point for this review. A casual reader of the AS50881 does not point to a limitation on the use of light weight wire constructions; there is no explicit limitation except that in section 3.8 “Wiring Selection” it states that, “the wire shall be selected in accordance with Appendix A of this specification”. Digging into the AS50881 Appendix A finds that there are two groups of wires, those that are permitted for use in open harness construction (with no additional sleeving protection) and protected harnesses (additional harness protection). Continued on page 48 What about Other Tests? Other tests listed in the AS4373 but are not included in the qualification for the AS22759/193 and /195 constructions would similarly show performance differences between the wires. These include: • Dielectric Constant • Corona Inception and Extinction Voltages (Also Know As Partial Discharge)