Technical Centre | UL

Documentation for UL registration

Information on UL registration and insulation systems for transformers

Many of our customers will, at the latest when they want to expand their business overseas, be confronted with the requirement for UL accreditation for their products.

This accreditation is issued by Underwriters Laboratories Inc. (abbrev. UL), following a usually extensive, time and cost intensive product testing with regard to electrical and fire safety. UL itself is, similar to European testing authorities (e.g. VDE), a non-governmental organisation that was founded in 1984 at the instigation of fire insurance companies in the USA at that time. (Accreditation/listing of a product by UL provides the manufacturer with greater legal security in the event, for instance, of damage occurring during the use/operation of the product sometime in the future (US Product liability laws!).)

In order to attain UL listing of an electronic product, the manufacturer must submit the complete product to UL for testing. In accordance with the end product testing criteria set down by UL, the product submitted for listing is tested for safety. In order to be able to significantly reduce the very cost intensive and often time-consuming testing overheads for the manufacturer of an electronic product in the course of UL accreditation, a large number of components that are required for the manufacture of an electronic product, have already been submitted by the manufacturers of the components to UL for testing. In the course of this, the reaction to fire of plastics and potting materials (e.g. self extinguishing properties, flammability), electrical insulation values and the thermal long-term behaviour of electrical insulation materials in particular are evaluated.

These so-called "recognized components" are, for instance, varnished copper wires, multi-layer surface insulation, printed circuit board base materials, plastics (e.g. for casings/housings), coil formers, impregnating agents, potting materials, insulation tubes etc.

Many manufacturers also have complete insulation systems for various temperature classes (B, F, H and higher classes) listed with UL. These UL insulation systems include all materials used in transformers as well as, for instance, coil bobbins, insulation of Cu/copper wires, impregnating agents, insulating foils, adhesive tapes, tubes, stranded wire insulation etc.

If, in the manufacture of a transformer, only insulation materials of a UL insulation system are use, it is thereby guaranteed that all insulation materials of this system within the authorised temperature range in which the transformer is operated will suffer no reduction of its electrical insulation properties that could cause a dangerous operating situation (fire-hazard, electric shock hazard).