The dependence of arcing duration and energy in break operations for automotive relays was analysed with breaking current/voltage waveforms. Endurance tests were conducted with AgSnO2, AgNi10 and AgNi0.15 contacts under the loads of resistance, lamp and inductance, respectively, at 14 VDC. The experimental results shows breaking current (or break arc) duration is usually low and stable before welding occurs. The welding may appear suddenly or randomly without any preceding cumulated increases in the arc duration, the quantity of electric charges, nor the arcing energy. The welded contacts may be re-opened in the later break operation and, thereafter, can keep on working normally for many times.