What is the maximum earth fault loop impedance for a TN-C-S system?

The maximum earth fault loop impedance for a TN-C-S system is 0.35 Ohms. This value is crucial because it ensures that the protective devices, such as circuit breakers or fuses, operate effectively in the event of a fault. The loop impedance must be low enough to allow sufficient fault current to flow, which in turn ensures that the protective devices can disconnect the fault within a specified time frame, thereby minimizing the risk of electric shock or fire.

In a TN-C-S system, which combines characteristics of TN and TT systems, the impedance needs to be well-defined to maintain safety standards and ensure reliable operation of the electrical installation. A loop impedance higher than this value could lead to a situation where the protective devices do not trip quickly enough during a fault condition, potentially allowing dangerous voltages to persist for an unsafe duration.

The other options represent values that exceed the maximum permissible earth fault loop impedance for this specific system, which could compromise electrical safety and system functionality.