Electrical cables are routinely exposed to several kinds of damaging chemicals in the environments they pass through. However, the most damaging of them all is chemical exposure to oil. Many industries and infrastructure settings use oil as a lubricant or as coolants. Such oils react with the polymers used in the cable insulation and jacketing to inflict molecular damage.
If this is ignored, oil can severely damage cables. This ultimately results in failure of the cable, system downtime and replacement expenses. With advanced production facilities such as in automotive assembly, requirements of better performance characteristics in renewable energy and regulatory changes, more people are now aware of oil damage to cables.
Fortunately, better cable manufacturing technology is now allowing cables to resist the effects of lubricating and cooling oils. However, it is necessary to know how oil degrades cables, how oil exposure problems can be diagnosed and how cables can be selected so that they resist oils over the long haul.
Insulation and jackets of cables are typically made of polymer compounds. Although they may have the same family name, not all these polymers show the same physical properties, including oil resistance. For example, some PVC compounds may show better oil resistance, while others have a higher degree of flame resistance. Manufacturers change the PVC formulation according to the properties and applications desired.
For example, addition of certain flame-retardants, stabilizers and filters allow PVC to exhibit enhanced characteristics of this type. However, improving or enhancing one characteristic usually comes at the cost of other performance traits being affected or being completely lost.
That explains why not all wire and cable insulations show equal performance with oil resistance in particular. The chemical, mechanical, environmental and electrical attributes vary depending on the individual compound formulations. To help promote resistance to fatigue and increased flexibility, most insulating compounds have a specific amount of plasticizers added to their individual formulations. When such compounds are exposed to processing oils for coolant or lubrication, the plasticizer diffuses from the compound or the material absorbs the oil.
With the plasticizer diffusing out of the compound, the oil causes insulation hardening, resulting in loss of flexibility and elongation properties. If oil is absorbed, the insulation swells and softens resulting in degradation of tensile properties.
In short, oil causes the insulating compound to lose its primary role virtually as an effective insulator. This creates a hazardous situation not only to the functioning of the industrial machinery to which it is connected, but possibly also to human life. Ultimately, this can result in expensive downtimes, expensive repairs and in the worst cases, replacement of the entire machinery.
Testing can help determine how a cable will react in environments containing industrial oil. UL has standardized these tests and they are commonly known as Oil Res I and Oil Res II tests. In these tests, cable samples are continuously immersed in IRM 902 Oil at elevated temperatures for specified periods. The mechanical properties of the cable samples are observed for physical damage caused by the exposure to oil. The latest UL standard for these tests is AWM Style 21098.