Subway stations: Seamlessly safe

A broken hairdryer, a defective socket outlet, or a damaged cable – electrical appliances or installations are one of the most frequent causes of fire. These hazards not only pose a significant risk in the private domain, but also in passenger traffic. The City of Nuremberg is now taking action by installing innovative arc fault detection devices in its subway stations.

As many as 400,000 passengers travel on the Nuremberg subway every day, which corresponds to almost four fifths of more than 500,000 inhabitants living in the Franconian metropolis. With so many passengers, transport safety and fire protection have an equally important role to play. Needless to say, fire protection is extremely important in subway stations.

Innovations underground

Nuremberg’s U1 line has been running from its starting point at Langwasser Süd since 1972. The line serves key transport hubs including the trade fair and the main train station. It is one of three subway lines run by operating company VAG Nürnberg together with the city’s buses and trams, and covers a total of around 41 kilometers of track.


What is special about the U1 is that it is Germany’s first driverless subway line. But while the underground rail system features state-of-the-art high technology, the stations are showing visual and technical signs of age. Between 2011 and 2015, the electrical systems along the line were upgraded, and the Scharfreiterring station was refurbished in 2015. As a statutory public transportation provider, VAG is also responsible for equipping the stations of the U1 line with the latest safety technology to meet current safety standards. And for good reason.

A major threat

Roughly one-third of all fires in Germany are caused by electricity. Some of the most common causes include faulty, defective, or damaged connections or cables. Electric system components that are not positioned far enough apart or are inadequately isolated can cause arcing. This danger can also arise when contacts are separated inside an electrical component or if the insulation is damaged. Arc fault detection devices protect against this danger: They detect internal arcs and deactivate the circuit automatically whenever necessary.

Best possible protection for passengers

The system is not just designed to ensure passengers can evacuate as quickly as possible in the event of a fire. The focus is also on fire prevention. Until just a few years ago, it was not technically possible to identify internal arc faults reliably. As operator of the local transport network, the City of Nuremberg has closed this major safety gap by using 5SM6 arc fault detection devices from the SENTRON series.


The arc fault detection device continuously analyzes the currents and high-frequency noise, while the integrated microcontroller immediately detects unwanted arcing faults. The key factor, however, is that they can differentiate between harmless interference generated by drilling machines, for example, and hazardous arcs. If internal arcs occur, the AFDD safely shuts down the circuit. The device is also maintenance-free, because it continuously monitors its own functional capability.

A convincing safety concept

The City of Nuremberg is convinced by the new technology: After testing an AFDD on the U2 line, it decided to include the device in the tender specifications for upgrading the stations’ electrical systems. A total of twelve AFDDs are monitoring one circuit each at three stations on the U1 subway line. At Klinikum Nord and Nordwestring – the new stations on the extended U3 subway line – arc fault detection devices from Siemens are now in use.


Picture credits: Siemens AG / W. Geyer

Whereas AFDDs have been mandatory in the U.S. for many years, the European IEC 60364-4-42 standard did not recommend their installation until 2014. Since the publication of the DIN VDE 0100-420 standard in February 2016, AFDDs are classed as the “recognized technical standard” in particularly hazardous areas. These areas include childcare facilities, retirement homes, storage facilities for flammable materials, laboratories, and train stations. If no AFDD is installed and a fire occurs, the legal status of the unit as the “recognized technical standard” means that the electrician responsible can be held liable.

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