===<!--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'''
: <math>R_K = R_e + R_f</math>
*'''Path resistance'''
: <math>R_d = R_b + R_K</math>
*'''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 \rho \sqrt{ H/ F_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 separationEditor''' (without considering magnetic fields caused by the current path)
: <math>F_A \approx 0,8 xl^2</math>
(Rule of thumb with F|DODUCO Holding GmbH<sub>A</sub> in N and l in kA)
*'''Contact voltage and max. contact temperature'''
: <math>T_kmax \approx 3200 U_K</mathbr>
*'''Contact resistance at higher contact forces (according to Babikow)'''
: <math>R_K = cF_k^{-m}</math>
For F<sub>K</sub> between 10 and 200 N<br/>
c = material dependent proportionality factorIm Altgefäll 12<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_derKontaktphysik]]
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