Wire mills around the world each manufacture wire with a variety of requirements and certifications governing their quality. In North America, you will most often see the markings of CSA and/or UL as well as markings specific to industries like automotive and aerospace such as SAE, CE, MIL-XXX etc. depending on application.
Every performance characteristic about a wire is defined within the certifications like maximum operating voltage, flame retardance and burn characteristics, temperature tolerances, insulation thicknesses, platings on conductors.
You can read more about the specifics of wire markings here.
Raw Wire Quality & Manufacturing Defects
When mills produce wire, their lines must be approved to the certifications required for the user of the product before running batches of product. Each UL standard will define the O.D (outer diameter), and conductor thickness in AWG as well as composition for the mill to create. Sometimes flaws in the creation process cause deformities on the circumference of the wire insulation causing different fails during wire harness production.
Wire Deformity: This is usually caused by wire being barreled while still too warm from the extruding process. This causes the insulation to become thin at any point along the wire.
The voltage ratings of wire rely on the insulation wall thickness in order to maintain safety from overheating and breaking down. When following IPC A 620 wire harness manufacturing standards, any more than a 20% breach of insulation thickness results in a defect. It is important to quality control the raw wire being used on certified products to maintain high quality and safety standards.
Here is an example of certified wire received that was found defective. In this case, the wire would not run through the automated cutting machinery during the wire harness manufacturing process and would have resulted in tooling damage:
Vulcanization vs Sliding Wire Jacket
What is Wire Vulcanization?
Vulcanization refers to when a strand or multiple strands of wire become imbedded into the insulation jacket of the wire during the creation process. When wire mills produce certified wire, the internal wire conductors are tightly bound with insulating materials surrounding them. Sometimes manufacturing errors cause the strands to loosen during the process and the insulation solidifies around the rogue conductors. It is impossible to manufacture certified products using wire that has been improperly manufactured like this because stripping it leads to removed strands and crimp failures.
on the other hand, sliding wire has the opposite problem. During creation, wire conductors are not cooled fully when the insulation is applied to their circumference and the copper conductors become separated from the insulation when it cools. The wire conductors can slide within the insulation of the wire making tight tolerance jobs extremely hard to manufacture due to many inaccuracies with length and stripped ends.
Tolerances & Specs
Sometimes wire arrives with wrong physical characteristics compared to their certification specs. When processing this wire on automated machinery, the speed of the machinery combined with tight tolerance application terminals can render the wire unusable. Although the terminals are produced for that specific gauge of wire, insulation can be over tolerance and physically not fit the insulation crimp of the terminal causing crimp failures, jams and downtime. It is important that these types of jobs are paired with wire produced by mills maintaining high quality wire.
Barrelled Wire vs Spools
Wire comes in two main packages, Spools and Barrels. There are profound differences in the resulting wire that comes off a spool compared to barreled wire and has quality implications.
Inherently, spools have a tighter diameter core in their center. Wire inherently has memory. This means that when wrapped around the spool tightly, the wire will remain in a coiled pattern even when it is removed from the spool. Not only can this be unsightly for the end user of the wire harness, it can also lead to automated machinery defects.
It is standard in the commercial industry to only use barreled wire on automated machinery because of the fail rates experienced when using spooled wire.
When aesthetics are required in applications where the wire harness is viewable on the final product, barreled wire is preferred for its enhanced visual appearance although the performance of both packages of wire are the same.
Certified Wire Importance
It is absolutely paramount that certified wire is used in products that humans interact with for safety reasons. Wire quality issues can cause not only electrical failures in products, but also pose safety hazards to users like electrical shock, fire and even mechanical hazards if wire crimps begin deteriorating that hold force.
We have seen unrated wire with different insulation thicknesses for the same wire gauge and even different wire conductor diameters for the same wire gauge. This wire would not hold up to the voltage ratings if used in a high voltage application. as well, it would likely cause increased heat due to the resistance of flow in smaller sections of copper.
Finding suitable certified wire can be challenging because of varying quality levels even in the certified wire industry. Over the many years we have vetted many different producers of wire and believe we can offer the very best quality within our supply chains. With a little effort, consistent results and reliable certified wire can be obtained.