FI switch: An ingenious invention that saves lives today

As a rule, these switches are located in the fuse box in the entrance area of ​​the apartment or in a storage room.

The inventor of the FI switch is Gottfried Biegelmeiera physicist from Vienna who was born in 1924 and whose name is known to very few outside specialist circles. His invention is now as commonplace as the seat belt in a car. Both save lives.

Electrical accidents common

Looking back to the 1950s: With the economic miracle, the electrification of households also began. There was little research into the effect of electricity on the human body. But defective cables, damp bathrooms and improper installations – contact with electrical devices sometimes led to death due to electric shock.

Although the patented “summary current circuit for ground fault detection” from the German company Schuckert & Co. had existed since 1903, these early systems were imprecise, expensive and unsuitable for household use.

How it works

This is where Biegelmeier came in as an inventor and as a scientist. Be Residual current circuit breakershort FI switch, continuously compares the current strength in the supply conductor (phase) and return conductor (neutral conductor). In normal operation both streams are identical. If current flows through a different route – for example through the human body when touching a defective device – the FI switch registers this difference (residual current) in milliseconds – faster than the human heart can react. An electromagnetic trigger then interrupts the circuit within 0.03 seconds.

Development laboratory

In January 1956, Biegelmeier registered his patent number 191492 for the insulation fault circuit breaker. In 1957, the physicist with a doctorate became head of the development department of the well-known cable and electrical engineering company Felten & Guilleaume (T&G) in Vienna and Schrems, where he further developed the FI switch. In his laboratory, Biegelmeier worked on a solution to the electrical accident problem. This combination of theoretical understanding and practical implementation made him a pioneer in electrical safety. In the following years, further patents were created in his development laboratory to refine residual current circuit breakers. According to the patent register, he filed patent number 197468 in March 1957, which contributed to the further development of the FI switch.

Billion dollar business

The market launch of the FI switch was a resounding success. Felten & Guilleaume recognized the potential and began series production. Other manufacturers followed suit, initially in Austria and Germany, and later worldwide.

Since 1980, the installation of FI switches has been required by law in every household in Austria. Germany, Switzerland and many other countries followed suit with similar regulations.

Today the international market for residual current circuit breakers is a billion-dollar business. And there are different types of FI switches. The type A switch, for example, is sufficient for normal household appliances, while type B is often used in PV systems.

Keen researcher

Companies such as Siemens, ABB, Schneider Electric and Eaton, the current owner of Felten & Guilleaume, and Schrack Technik produce millions of switches every year. The FI switch has been standard in new buildings and renovations for more than 40 years – not only in residential buildings, but also in commercial and industrial facilities.

But Biegelmeier was not only an inventor, but also a keen scientist. He conducted intensive research into the effects of electrical current on the human body, and also carried out numerous self-experiments under medical supervision. His scientific work on so-called body impedances, touch voltages and the physiological consequences of electric shock received worldwide recognition and formed the basis for safety standards. The International Electrotechnical Commission (IEC) and other standards bodies drew on Biegelmeier’s findings.

Numerous prizes

Biegelmeier was honored with numerous awards for his achievements. Particularly prestigious: In 1995, together with two other researchers, he received the Wilhelm Exner Medal, one of the highest awards for technical and scientific achievements in German-speaking countries. A year later he founded the non-profit private foundation Elektroschutz.

But despite the recognition, Biegelmeier remained modest. He avoided the limelight, rarely gave interviews and focused on his work. It is said that he was not a man of big words, but a man of facts and results. Gottfried Biegelmeier died on July 8, 2007 in Lunz am See in the Mostviertel.