earth fault loop impedance

circuit protection should operate in the event of a fault to earth. The speed of operation of the protective device is of extreme importance and will depend on the impedance of the earth fault loop path.

• the circuit protective conductor (CPC)
• the consumer’s earthling terminal and earthing conductor
• the return path, either metallic or earth itself
• the earthed neutral of the supply transformer
• the transformer winding
• the phase conductor from the transformer to the fault.

below Figure is a simplified version of the loop path.

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