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===<!--6.4.2 -->Contact Physics – Formulas===
*'''Constriction resistance''' : <br math>R_e = \rho/>R<sub>e2a</submath> = D/2a
(Single spot contact according to Holm; circular touching spot between clean
contact surfaces)
(Multi-spot contact according to Holm without influence between the N
individual spots)
(Multi-spot contact according to Greenwood considering the influence between
the spots)
*'''Contact Path resistance''' : <br />R<sub>K</submath> R_d = R<sub>e</sub> R_b + R<sub>fR_K</submath>
(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)
(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 \approx 0,8 x I<sup>xl^2</supmath>(Rule of thumb with F<sub>A</sub> in N and I l in kA)
*'''Contact voltage and max. contact temperature''' : <br />T<sub>kmax</submath> T_kmax \approx 3200 U<sub>KU_K</submath>
*'''Contact resistance at higher contact forces (according to Babikow)''' : <math>R_K = cF_k^{-m}<br /math>RFor F<sub>K</sub> = cF -m KFor F between 10 and 200 N K<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 Guidance Guideline Data for the Use of Electrical ContactsContact Design#References|References]] [[de:Formeln_aus_der_Kontaktphysik]]