===6.4.2 Contact Physics – Formulas==={| |'''Editor''':|DODUCO Holding GmbH<br> Im Altgefäll 12<br>
*'''Constriction resistance''' : $R_e = \rho75181 Pforzheim /2a$(Single spot contact according to Holm; circular touching spot between cleancontact surfaces): $R_e = \rho/2Na$(Multi-spot contact according to Holm without influence between the Nindividual spots): $R_e = \rho/2 x \sum a_i + 3 \pi \rho /32N^2 x \sum \sum (s_ij) i \neq j$(Multi-spot contact according to Greenwood considering the influence betweenthe spots)Germany<br>
*'''Contact resistance''': $R_K = R_e Phone + R_f$49 (0) 7231 602-0<br>
*'''Path resistance''' Fax +49 (0) 7231 602-398<br>: $R_d = R_b + R_K$
*'''Contact resistance and contact force'''Mail: $R_K = 280\rho \sqrt[3]{E (F_K \cdot r)} $ (According to Holm model for film-free spherical contact surfaces with plasticdeformation of the contact material; F<sub>k</sub> < 1 N for typical contact materials): $R_K = 9000 \rho \sqrt{ H/ F_K}$(According to Holm model for film-free spherical contact surfaces with plasticdeformation 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) : $F_A \approx 0,8 xl^2$(Rule of thumb with F<sub>A</sub> in N and l in kA) *'''Contact voltage and maxinfo@doduco. contact temperature''': $T_kmax \approx 3200 U_K$ *'''Contact resistance at higher contact forces (according to Babikow)''' : $R_K = cF_k^{-m}$For F<sub>K</sub> between 10 and 200 Nnet<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]]
