BU I LDI NG SOLUT IONS
— Harmonics and high frequency leakage current
The immunity of residual current devices to high-frequency leakage currents is ensured by compliance with standard IEC 61543 whose requirements are based on standards IEC 61000-4-3; IEC 61000-4-6 and IEC 61000-4-16.
The installation of a residual current circuit breaker upstream of another residual current circuit breaker without special precautions can create selectivity problems: a fault that causes a residual current in a downstream circuit leads to the tripping not only of the residual current circuit breaker that protects the downstream circuit but also of the upstream one, unless the fault lasts longer than a certain period of time.
The general rule for ensuring selectivity is based on two basic conditions:
• the minimum non-intervention time of the upstream residual current device must be greater than the interruption time of the downstream residual current devices; • the rated tripping differential current of the upstream device must be at least 3 times the rated tripping differential current of the downstream installed earth leakage circuit breakers.
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