If the circuit is using the earth leakage protection function on the Micrologic 4.2/4.3 or Micrologic 7.2/7.3 trip units then you will need to refer to the maximum ZS values printed in the BS7671 wiring regulations. For the current printing this is table 41.5.

If the circuit is not using the earth leakage protection function on the trip units. Turned the earth leakage dial (IΔn) to OFF. Then you can use the maximum zs values for the Micrologic 2.2 trip units printed in the below FAQ.

What is the maximum earth loop Impedance Zs value for the circuit breakers used in the Powerpact 4 panel board? | Schneider Electric UK

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