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How is the earth leakage and ground fault protection achieved in Masterpact circuit breakers?

  1. Micrologic 6 provides residual earth-fault protection OR source ground return protection.
  2. Micrologic 7 provides earth-leakage protection.
Residual earth-fault protection is provided by calculating the vectorial sum of the currents of instrument CT secondary. In 3P circuit breakers the CT on the neutral conductor is outside the circuit breaker. In our offer this CT is the "external sensor for earth-fault and neutral protection". For 4 pole circuit breakers we don't need the external neutral sensor because it is integrated in the circuit breaker's neutral pole.

Source ground return protection is using a special external sensor (SGR + MDGF). This function directly measures the fault current returning to the transformer via the earth cable. The insulation fault current is measured in the neutral-earth link of the LV transformer.
The residual earth-fault and source ground return protections can not be achieved at the same time on one circuit breaker with Micrologic 6.
In the diagrams before please see the different connection diagrams for earth-fault and source ground return protections.
Earth-leakage protection function primarily protects people against indirect contact because an earth leakage current can provoke increase in the potential of exposed conductive parts. For earth-leakage protection an external rectangular sensor is needed. The external rectangular sensor is needed for the earth leakage protection for all 3P and 4P circuit breakers.

Earth-leakage protection can be achieved ONLY on Micrologic 7 trip units using an external rectangular sensor.

  Residual ground fault Source ground return Earth leakage
Micrologic 6 External neutral sensor for 3P circuit breakers SGR + MDGF NOT POSSIBLE
Micrologic 7 NOT POSSIBLE NOT POSSIBLE External rectangular sensor

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