The formulae express the power loss occurring in metallic armour, reinforcement of steel pipes of a cable in terms of an increment $\lambda_2$ of the power loss in all conductors. The IEC standard has formulae for three distinctive cases: Non-magnetic armour or reinforcement, Magnetic armour or reinforcement, and losses in steel pipes.

To be noted:

Symbol
$\lambda_{\mathrm{2}}$
Unit
-
Formulae
$\frac{R_{\mathrm{s}} \lambda_{\mathrm{1}}}{R_{\mathrm{A}} + R_{\mathrm{s}}}$non-magnetic armour
$\frac{R_{\mathrm{s}} W_{\mathrm{sA}}}{W_{\mathrm{c}} \left(R_{\mathrm{A}} + R_{\mathrm{s}}\right)}$magnetic armour, multiple single-core cable
$\frac{3.82 \cdot 10^{-5} A_{\mathrm{a}} \omega \left(1.48 r_{\mathrm{c}} + t\right)^{2}}{R \left(95.7 A_{\mathrm{a}} + d_{\mathrm{a}}^{2}\right)^{2}} + \frac{6.2 \cdot 10^{-15} \omega^{2}}{R R_{\mathrm{A}}}$magnetic armour, two-core cable
$\frac{1.64 R_{\mathrm{A}} s_{\mathrm{c}}^{2}}{R d_{\mathrm{a}}^{2} \left(\frac{7672900000000.0 R_{\mathrm{A}}^{2}}{\omega^{2}} + 1\right)}$magnetic steel wire armour, three-core cable, round conductors
$\frac{0.358 R_{\mathrm{A}} d_{\mathrm{c}}^{2}}{R d_{\mathrm{a}}^{2} \left(\frac{7672900000000.0 R_{\mathrm{A}}^{2}}{\omega^{2}} + 1\right)}$magnetic steel wire armour, three-core cable, sector-shaped conductors
$\frac{4.0 \cdot 10^{-11} f^{2} s_{\mathrm{c}}^{2} \left(0.225 \delta + \frac{1}{\delta }\right)}{R d_{\mathrm{a}} \left(\frac{d_{\mathrm{a}}}{\delta \mu_{\mathrm{s}}} + 1\right)^{2}}$magnetic steel tape armour, three-core cable
$\lambda_{\mathrm{2}} \left(- \frac{0.666666666666667 R}{R_{\mathrm{s}}} \lambda_{\mathrm{1cb}} + 1\right)$magnetic armour, three-core cable, individual screen/sheath
$\frac{R_{\mathrm{A}} W_{\mathrm{A}}}{W_{\mathrm{c}}}$magnetic armour but without screen/sheath
$0$otherwise
Related
$A_{\mathrm{a}}$
$d_{\mathrm{a}}$
$d_{\mathrm{c}}$
$\lambda_{\mathrm{1}}$
$\lambda_{\mathrm{1cb}}$
$\mu_{\mathrm{s}}$
$\omega$
$R_{\mathrm{A}}$
$r_{\mathrm{c}}$
$W_{\mathrm{A}}$
$W_{\mathrm{c}}$
$W_{\mathrm{sA}}$
Used in
$I_{\mathrm{c}}$
$\lambda_{\mathrm{1}}$
$q_{\mathrm{2_{\mathrm{1}}}}$
$q_{\mathrm{2_{\mathrm{2}}}}$
$T_{\mathrm{eq}}$
$\theta_{\mathrm{c_{\mathrm{z}}}}$
$W_{\mathrm{A}}$
$W_{\mathrm{I}}$