Factor for fictitious diameter by Neher

This factor depends on the cable diameter and the transient period and usually it lays in the range of 0.97 to 1.37 for cable diameters of up to 100 mm. For larger diameters (e.g. ducts and tunnels), the value increases with the diameter of the source and the Neher method is not recommened.

Neher empirically evaluated a value of 1.02 for the factor $K_x$ under the assumption of a sinusoidal load variation with a transient load period $\tau$ of 24 hours and a soil diffusivity $\delta_{soil}$ of 0.5*10-6 m$^2$/s.

Used in