As we go in to the 21st century, electrical insulation systems (EIS) are playing an ever more important role in the global manufacturing of transformers, motors, relays, contractors, lighting ballasts, and a host of other electrical applications. Basically, such systems are groups of materials that through extensive testing are recognized to be well suited for electrical applications at a given temperature or "class" and at specified material thicknesses.

Fig 1. Wire Wound Coil

In designing a transformer or motor, for example, there have been historically two basic ways of selecting the materials going into the product: the wires, tapes and thermoplastic used were selected either by the individual material thermal and performance recognitions (e.g. the UL RTI of each material by itself) or by the collective EIS recognition which is a measure of how the group of materials selected behave together in a common environment.

As an example, consider a simple coil form molded in thermoplastic holding a wire coated with an enamel (Figure 1). The coil form and enamel-coated wire may each have a UL RTI of 155°C. However, when used together in a Class 155 (F) environment, the thermoplastic coil form may actually react chemically with the enamel and destroy the coil.

The Systems Approach
Systems testing eliminates this possibility and helps build confidence that when used properly, the group of materials in a UL recognized EIS will help produce a quality product for the global market place.

As another example, the relay in Figure 2 illustrates why it is so important to test materials together simultaneously. Possible destructive outgassing from one or more components can usually be determined in systems testing.

Fig 2. Typical Electromechanical Relay		Fig 3. Encapsulated Transformer

Systems testing is also important for encapsulated coils where the wound coils are completely encased in the overmolded plastic. For example, for the Valentine transformer shown in Figure 3, EIS testing was important in material selection. Other small transformers have been successfully encapsulated with Rynite® PET as well.

Systems are recognized under Underwriters Laboratories (UL) and International Electrotechnical Commission (IEC) standards UL 1446 and IEC 60085, respectively, with qualifying tests described in IEEE (Institute of Electrical and Electronic Engineers) documents. More recently, the IEC has moved to standardize the testing and evaluation of electrical insulation systems and to provide a uniform means of qualifying them. The result has been the recent adoption of:

• IEC 61857 - Procedure for Thermal Evaluation of EIS
• IEC 61858 - Qualification of Additional Materials in EIS

Also under development by the IEC are standards for encapsulated coils and a revision of IEC 60085, the Thermal Evaluation and Classification of Electrical Insulation. The target date for these two new standards is 2002. Taken as a group, these new IEC electrical insulation system standards will meet broad industry consensus that in this application area there should be one set of standards and test procedures worldwide.

With IEC 61857 and IEC 61858 now accepted as global standards, well over 190 nations around the world that automatically accept IEC standards as National Standards are now in the process of establishing EIS as their basic foundation for electrical applications. What this means is that a system once restricted to UL recognized applications in the USA is now a global system required for electrical applications anywhere that need to be compliant to IEC standards.

DuPont and EIS | EIS Explained | DuPont Materials
Selecting the Right EIS | Encapsulated Components | Wire Substitutions