Siemens has added arc-fault detection units for circuits with larger electrical consumers to protect them from cable fires caused by defective installations
Siemens is expanding its range of arc-fault detection (AFD) units from the 5SM6 product line by adding a version for rated currents up to 40 amperes (A). The new devices are used in electrical installations and protect against electrical fires. They are ideal for circuits with larger electrical consumers, for instance with motors as well as for applications in European countries with circuits larger than 16 A, such as in Great Britain, Belgium, and the Netherlands. AFD units react to serial arcing faults that can be caused by defects in electrical installations, and they safely disconnect circuits within fractions of a second. Serial arcing faults can lead to cable fires and are not detected by conventional protective devices such as residual current circuit breakers and miniature circuit breakers. Protection against serial arcing faults was recently recognised as state of the art and incorporated into the global IEC standard as well as into DIN VDE 0100-420 applicable throughout Germany.
Siemens has offered AFD units for branch circuits up to 16 amperes since 2012.
The publication of the German standard DIN VDE 0100-420:2016-02 “Low voltage electrical installations – Part 4-42: Protection for safety – Protection against thermal effects” mandates the installation of AFD units in Germany for certain application areas. These areas include woodworking companies, wooden houses, paper and textile factories or laboratories, public buildings, railway stations and airports, and bedrooms and living rooms of daycare centres and retirement homes.
Existing electrical installations can easily be retrofitted with 5SM6 AFD units in the version up to 40 A. In developing the new versions, Siemens further improved the use of the AFD units. The mechanical tripping lever was replaced by an LED-illuminated button, which serves as both a reset and a test button. The LED uses different colours to indicate normal operation or a fault. The device automatically conducts a self-test every 11 hours.
The AFD units from Siemens detect all types of arcing faults by capturing more than just the current and voltage. In addition, the 5SM6 AFD units constantly measure the high-frequency noise with regard to amount, stability, and duration. In conjunction with intelligent software, integrated filters process, analyse, and evaluate these signals in accordance with a wide range of criteria in order to determine, for example, the total energy, arcing energy, the plateau of the arcing voltage, arcing stability, and the appearance of flames. If the conditions of an arcing fault are met, the connected circuit is disconnected within fractions of a second. This technology makes it possible to detect and prevent fire hazards from the electrical wiring at an early stage all the way to the terminal device.
Arcing faults in electrical wiring or systems are among the most frequent causes of fire. A distinction should be made between serial and parallel arcing faults. Parallel arcing faults occur between the phase conductors to ground or protective conductors (PE), between two phase conductors, or between phase conductors and neutral conductors. Serial arcing faults can occur when a conductor is interrupted or as a result of loose contacts.
Some of the most frequent causes of serial arcing faults include damaged cable insulation (due to nails, screws, or mounting clips, for example), crushed cabling when installed through open doors and windows, cable breaks due to kinking, bent connectors and cables due to lose contacts and connections in switches or outlets. In addition, environmental influences such as heat, moisture, gases, and – in outdoor areas – UV radiation and gnawing rodents can damage the cables, and conductive contamination and condensation water can produce undesirable contacts.