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===<!--6.4.2 -->Contact Physics – Formulas===
*'''Constriction resistance'''
*'''Path resistance'''
: <math>cR_d R_d = R_b + R_K</math>
*'''Contact resistance and contact force'''
(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 \rho \sqrt{ H/ FKF_K}</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)
: <math>F_A \approx 0,8 /cdot I_2xl^2</math>(Rule of thumb with F<sub>A</sub> in N and I l in kA)
*'''Contact voltage and max. contact temperature'''
: T_k max</submath> T_kmax \approx 3200 U<sub>KU_K</submath>
*'''Contact resistance at higher contact forces (according to Babikow)''' : <br /math>R<sub>KR_K = cF_k^{-m}</submath> = cF -m KFor F<sub>K</sub> between 10 and 200 N<br/>c = material dependent proportionality factor<br/>
m = shape dependent exponent of the contact force
{| class="twocolortable scalable" style="text-align: left; font-size: 12px; width:45%;"
|-
!Material combination
!c
|-
|Copper - Copper
|(0.08 bis 0.14) x 10<sup>-3</sup>
|-
|Aluminum - Aluminum
|(3 bis 6,7) x 10<sup>-3</sup>
|-
|Brass - Brass
|0.67 x 10<sup>-3</sup>
|-
|Steel – Silver
|0.06 x 10<sup>-3</sup>
|-
|Steel – Copper
|3.1 x 10<sup>-3</sup>
|-
|Steel – Brass
|3.0 x 10<sup>-3</sup>
|}
{| class="twocolortable scalable" style="text-align: left; font-size: 12px; width:45%; "
|-
!Contact shapes
!m
|-
|Flat – Flat
|1
|-
|Pyramid – Flat
|0.5
|-
|Sphere – Flat
|0.6
|-
|Sphere – Sphere
|0.5
|-
|Multi-strand brush - Flat
|1
|-
|Current bar (Busbar) contact
|0.5 - 0.7
|}
<div class="clear"></div>
==References==
[[Application Tables and Guideline Data for Use of Electrical Contact Design#References|References]]
[[de:Formeln_aus_der_Kontaktphysik]]
