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→5.1.2 Pure Copper
Copper is used in electrical engineering mostly because of its high electrical conductivity<ref>As units for electrical conductivity MS/m and m/Ω.mm<sup>2</sup> are commonly used. Frequently – and mostly in North America – the % IACS value (International Annealed Copper Standard) is also used, where 100% is equivalent to 58 MS/m or m/Ωmm<sup>2</sup> .For the description of mechanical strength properties the units of N/mm<sup>2</sup> or MPa are most commonly used:
1 MS/m = 1 m/Ωmm<sup>2</sup>
1 MPa = 1 N/mm<sup>2</sup></ref> which with 58 MS/m (or m/Ωmm²) is only slightly below that of silver. Other advantages of copper are its high thermal conductivity, corrosion resistance, and its good ductility. The work hardening properties of ETP copper is illustrated in <xr id="fig:Strain hardening of Cu-ETP by cold working" />. The increase in strength achieved by cold working can be reversed easily by subsequent annealing. The softening properties are strongly dependent on the preceding cold working percentage ''(<xr id="fig:Softening of Cu-ETP after annealing for 3hrs after 25% cold working"/> and <xr id="fig:fig5.3Softening of Cu-ETP after annealing for 3hrs after 50% cold working"/> 5.3)''.
The purity of technically pure and un-alloyed copper used for electrical applications depends on the type used and ranges between > 99.90 and 99.95
<xr id="fig:Softening of Cu-ETP after annealing for 3hrs after 25% cold working"/> Fig. 5.2: Softening of Cu-ETP after annealing for 3hrs after 25% cold working
<xr id="fig:fig5.3Softening of Cu-ETP after annealing for 3hrs after 50% cold working"/> Fig. 5.3: Softening of Cu-ETP after annealing for 3hrs after 50% cold working
</figure>
<figure id="fig:fig5.3Softening of Cu-ETP after annealing for 3hrs after 50% cold working">
[[File:Softening of Cu ETP after annealing 50.jpg|left|thumb|<caption>Softening of Cu-ETP after annealing for 3hrs after 50% cold working</caption>]]
</figure>
