View source for Contact Physics – Formulas

===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/32N² 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</sub> = R<sub>e</sub> + R<sub>f</sub>

*'''Path resistance''' cR<sub>d</sub> = R<sub>b</sub> + R<sub>K</sub>

*'''Contact resistance and contact force''' <math>R_K = 280D ³ E(F · r) K</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</sub> 0,8 x I<sup>2</sup>(Rule of thumb with F<sub>A</sub> in N and I in kA)

*'''Contact voltage and max. contact temperature''' <br />T<sub>kmax</sub> 3200 U<sub>K</sub>

*'''Contact resistance at higher contact forces (according to Babikow)''' <br />R<sub>K</sub> = cF -m K
For F<sub>K</sub> between 10 and 200 N
c = material dependent proportionality factor
m = shape dependent exponent of the contact force

==References==
[[Application Tables and Guideline Data for Use of Electrical Contact Design#References|References]]