​Safety Update: Danger when using incorrect residual current devices (RCD / RCCB) in domestic electrical installations

10 Dec 2020

Safety Update: Danger when using incorrect residual current devices (RCD / RCCB) in domestic electrical installations. 

Residual current circuit breakers (RCCB) switch off the power supply when dangerously high residual currents occur. In this way, they protect people, animals and installations.

Many electrical installations in buildings were built with standard RCD / RCCB type A. 
Since many buildings today also have frequency converter/inverter drives (e.g. in treadmill ergometers, lifts, heat pumps, heaters, washing machines, tumble dryers, air-conditioning systems, ventilation systems, etc.), the standard RCD / RCCB type A often are no longer sufficient.

The RCD / RCCB must therefore also be universal current sensitive in such buildings / rooms, because the leakage currents of a frequency converter have, in addition to alternating current, a considerable direct current component or smooth direct fault current. High-frequency leakage currents with high amplitude can also occur in frequency inverters with EMC filters and long shielded motor supply cables.
In the case of a mixed form (smooth DC residual current superimposed by AC residual current), the AC residual current can only be transmitted weakened or not at all, since the iron core is partially to completely premagnetised by the smooth DC residual current.
If the right RCD / RCCB is selected, one of its functions is to interrupt the circuit if a person suffers an electric shock, e.g. due to insulation damage to a cable, because a sensitive RCD / RCCB then recognises this "residual current" as a "residual current".

In extreme cases, if an incorrectly selected RCD / RCCB is used and, for example, frequency converter drives of the above-mentioned devices are operated at the same time, a standard RCD / RCCB of type A may not trip in the event of an error. Therefore, in the worst case, there may also be a danger to human life.

Please also observe DIN VDE 0100-530 ("Setup of low-voltage installations - Part 530: Setup and installation of equipment - Switchgear and controlgear") which requires type B residual current devices in certain installations.

h/p/cosmos recommends RCD / RCCB of type B for the relevant building installation when using running belts with frequency converters.

RCD / RCCB of type B are all-current sensitive. They protect against pulsating and alternating residual currents, residual currents with mixed frequencies and smooth DC residual currents at frequencies up to 150 kHz.

h/p/cosmos recommends RCD / RCCB types B of the manufacturers: Doepke or SIEMENS

There are a few RCD / RCCB types B which trip too early ("over-sensitive") during operation with frequency inverter drives when the device is not equipped with a potential-isolation transformer. In such a case you can either install a differeht RCD / RCCB Type B in your domestic building installation or alternatively you can  retrofit a special leakage current reduction filter into your h/p/cosmos treadmill: Article order number of the leakage current reduction filter: cos103565-01ret

Further information can also be found on the websites or operating instructions of corresponding manufacturers or in technical literature.