Source impedance - earth fault loop impedance for protective devices to BS EN 60898 & BS EN 60947-2

It might help to refer to BS 7671's definitions:  Zs - is "earth fault loop impedance" (p53) and in turn "Earth fault loop impedance" is defined as:

The impedance of the earth fault current loop starting and ending at the point of earth
fault. This impedance is denoted by the symbol Zs.
The earth fault loop comprises the following, starting at the point of fault:
(a) the circuit protective conductor; and
(b) the consumer’s earthing terminal and earthing conductor; and
(c) for TN systems, the metallic return path; and
(d) for TT and IT systems, the Earth return path; and
(e) the path through the earthed neutral point of the transformer; and
(f) the transformer winding; and
(g) the line conductor from the transformer to the point of fault.

AJJewsbury said:

(c) for TN systems, the metallic return path; and

I like the way that, for such TN systems, there is no mass of Earth involvement in said Earth fault at all.     

Unless, of course, it's the unlabelled 

AJJewsbury said:

the point of fault

(mentioned twice; start & end... ).

AJJewsbury said:

(c) for TN systems, the metallic return path; and

I like the way that, for such TN systems, there is no mass of Earth involvement in said Earth fault at all.     

Unless, of course, it's the unlabelled 

AJJewsbury said:

the point of fault

(mentioned twice; start & end... ).