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===<!--6.4.2 -->Contact Physics – Formulas===
*'''Constriction resistance''' : <br /math>Re R_e = D\rho/2a</math>
(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 /math>RK R_d = Re R_b + RfR_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) kRK : <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 xl^2</math>(Rule of thumb with F<sub>A</sub> in N and l in kA) *'''Contact voltage and max. contact temperature''': <math>T_kmax \approx 3200 U_K</math>
*'''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 factor<br/>
m = shape dependent exponent of the contact force
==References==
[[Application Tables and Guidance Guideline Data for the Use of Electrical ContactsContact Design#References|References]] [[de:Formeln_aus_der_Kontaktphysik]]