Percussion drills, circular saws or electrical gardening appliances, such as hedge trimmers and lawn mowers – the list of electrical tools is long and resembles the range of products offered by do-it-yourself markets which appear out of nowhere. Although the electrical motors of these tools are small motors, they comprise a good deal of well-contrived technology, because they often have to withstand harsh conditions, such as:

• High current densities
• Vibrations
• Exposure to dust
• High speeds
• High torques
• Excellent radio interference suppression
• If possible low-noise operation
• Inclement weather.

The current transfer in these products is carried out by carbon brushes which have especially been optimised for the respective applications. For example in hedge trimmers, they have an excellent heat dissipation capacity and maintain good electrical contact in spite of permanent vibrations, and are resistant to wear and tear. In professional tools, the carbon brushes equipped with a special stranded wire signal the requirement of replacing the brushes 8 to 10 operating hours before the end of the brushes' life time. This makes sure that the tool still works for a whole working day, and replacement can be scheduled without problems. In modern vacuum-cleaners, special measures are required to cope with high speeds of up to 60,000 r.p.m. at low wear-and-tear.

The basic materials for the individual applications are carbon-graphite materials. Amongst other features, they are characterised by a wide resistance range (35 – 3000 µOhm), a high material strength and a good protection against burnout. Additional impregnation measures improve their running properties. The impregnation agents used comprise resins, plastic materials and other organic substances, as well as metals and salts.