This is the multiplication factor for cross-bonded earthing.

When the lengths of the three cable sections are not known, $p_{cb}$ should be set to 1, and $q_{cb}$ to 1.2, giving a value for $f_{cb}$ slightly below 0.004.

For two single core cross-bonded cables, which is not covered in the IEC standard, $f_{cb}$ is set to 0.004.

When all the lengths of the three cable sections are identical, $f_{cb}$ becomes zero.

Symbol
$f_{\mathrm{cb}}$
Unit
-
Formulae
$\frac{1}{\left(p_{\mathrm{cb}} + q_{\mathrm{cb}} + 1\right)^{2}} \left(p_{\mathrm{cb}}^{2} - p_{\mathrm{cb}} q_{\mathrm{cb}} - p_{\mathrm{cb}} + q_{\mathrm{cb}}^{2} - q_{\mathrm{cb}} + 1\right)$three-phase systems
$\frac{p_{\mathrm{cb}}^{2} - p_{\mathrm{cb}} + 1}{\left(p_{\mathrm{cb}} + 1\right)^{2}}$two-phase systems
$0$single phase
Related
$a_{\mathrm{S1}}$
$a_{\mathrm{S2}}$
$a_{\mathrm{S3}}$
Used in
$\lambda_{\mathrm{1c}}$