The loss of insulation between normally live conductors and exposed-conductive-parts may generate an earth fault, which represents a danger for electrical systems and for people safety. This technical paper by ABB SACE provides the necessary guidelines for the correct implementation of the company's 'Double G' low voltage (LV) circuit-breakers:
- Earth faults downstream of the circuit-breaker on the secondary side of the medium/low voltage (MV/LV) transformer (unrestricted earth faults or downstream earth faults);
- Earth faults between the transformer secondary windings and its cables connected to the circuit-breaker terminals (restricted earth faults or upstream earth faults).
The Double G can distinguish between each type of fault, restricted and unrestricted, because of a 'chrono-amperometric' discrimination, and to the MV/LV integration. It is always available on new Emax circuit-breakers equipped with PR123/P LSIG trip units, and on X1 circuit-breakers equipped with PR333/P LSIG trip units. The Double G function is easy to install and doesn’t require special wiring.
To see the full and extensive PDF document, which is highly detailed and very comprehensive, please click on the download button below (2.94MB file size). Alternatively, go to http://search.abb.com/library/Download.aspx?DocumentID=1SDC007403G0201&LanguageCode=en&DocumentPartId=&Action=Launch