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===6.4.2 Contact Physics – Formulas===
*'''Constriction resistance''' : <math>R_e = \rho/2a</math>
(Single spot contact according to Holm; circular touching spot between clean
contact surfaces)
: <math>R_e = \rho/2Na</math>
(Multi-spot contact according to Holm without influence between the N
individual spots)
: <math>R_e = \rho/2 x \sum a_i + 3 \pi \rho /32N^2 x \sum \sum (s_ij) i \neq j</math>
(Multi-spot contact according to Greenwood considering the influence between
the spots)
*'''Contact resistance''' R: <sub>K</submath> R_K = R<sub>e</sub> R_e + R<sub>fR_f</submath>
*'''Path resistance''' cR: <sub>d</submath> cR_d = R<sub>b</sub> R_b + R<sub>KR_K</submath>
*'''Contact resistance and contact force''' : <math>R_K = 280\rho \sqrt[3]{E (F_K \cdot r)} </math>
(According to Holm model for film-free spherical contact surfaces with plastic
deformation of the contact material; F<sub>k</sub> < 1 N for typical contact materials)
: <math>R_K = 9000 D H/ FK</math>
(According to Holm model for film-free spherical contact surfaces with plastic
deformation of the contact material; F<sub>k</sub> > 5 N for typical contact materials)
*'''Dynamic contact separation''' (without considering magnetic fields caused by the current path) : <br />F<sub>A</submath> F_A 0,8 x I<sup>2/cdot I_2</supmath>(Rule of thumb with F<sub>A</sub> in N and I in kA)
*'''Contact voltage and max. contact temperature''' <br />T<sub>kmax: T_k max</sub> 3200 U<sub>K</sub>
*'''Contact resistance at higher contact forces (according to Babikow)''' <br />R<sub>K</sub> = cF -m K
