Norden, 22/01/2014. Innovation from Doepke: The DFS 4 B+ MI protects existing systems where the upstream protective measure is unknown or consists of a Type A residual current circuit-breaker. If changing the upstream device is not desirable for reasons of cost, this circuit-breaker provides a safe alternative.

According to the installation regulations, a Type A residual current circuit-breaker that is sensitive to pulsating currents must not be inserted upstream of a Type B protection measure, as smooth DC currents greater than 6 mA can pre-magnetise the transformer core of a Type A circuit breaker, thereby 'blinding' it. The protection function is no longer fulfilled. In existing systems, it is not always known which protection measure is present. This is the case, for example, with building-site distribution boards or mobile systems with portable electric socket combinations. It is not always possible, however, to replace the upstream residual current circuit-breaker if the operator of the distribution board is not also the owner of the electrical installation they are using. As soon as there is a possibility of residual currents not equal to the operating frequency or of smooth direct residual currents, the use of an AC-DC sensitive residual current circuit-breaker is essential. The new AC-DC sensitive Doepke DFS 4 B+ MI residual current circuit-breaker provides a safe solution to this problem; it can be inserted quite safely downstream of a Type A residual current circuit-breaker as its DC triggering threshold is 6 mA. The downstream electrical installation will therefore be isolated from the network if there is a DC residual current exceeding 6 mA. A dangerous pre-magnetisation of the upstream Type A RCD is therefore averted.

The Doepke DFS 4 B+ MI also combines familiar properties such as the compact housing with a width of four module widths, increased surge current strength for the highest possible level of system availability, and an increased residual current detection range of up to 20 kHz. The devices are available with a rated current of 16 A to 63 A and with a rated residual current of 30 mA. The tripping characteristic curve conforms to the requirements of Type B+ and thus fulfils fire prevention requirements.

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