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To safely withstand short circuit currents high requirements are imposed on the weld resistance of the materials used for the mating contacts. During short circuit switching the contact force between the contacts pairing is reduced by electromagnetic forces. Above a certain device specific current value the contacts will separate. This generates an electrical arc with contact material melting at its root points. During the next closing of the contacts this can cause contact welding, prohibiting the opening of the contacts during a subsequent short circuit and therefore eliminating the safety function of the switching device.
<figtable id="tab:Testing for the Short Circuit Breaking Capacity of Low Voltage Power Switches According to IEC/EN IECEN 60947-2 (Shortened Summary)">
'''Table 13.3: Testing for the Short Circuit Breaking Capacity of Low Voltage Power Switches According to IEC/EN 60947-2 (Shortened Summary)'''
{| class="twocolortable" style="text-align: left; font-size: 12px"
|-
|-
|Test conditions
|Ue<br />cosn depends on value of current I in kA, i.e<br/>6 < l < 10 <br /> 10 cosn0.5 <br /> < l < 20 <br />cosn0.3<br />20 < l < 50<br />cosn0.25<br />50 < l cosn 0.2
|Non-inductive or slightly inductive loads, resistance furnaces
|}
</figtable>
===13.4.3 Testing According to UL and CSA===
