On DC contact opening, There is an immediate flow of current into the capacitor, this tends to retain any arc that starts to form, as previous noted, I have cured these high energy arcs by magnetic blow-out.
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How does a low resistance that shunts the current away from an arc extend the arc time??? Also, this is a low voltage inductive load, not a high voltage load. So the inductive voltage spike amplitude is dependent on the rate of change of current through the inductance of the solenoid. So if the current is shunted from the contacts opening to charge a capacitor, the rate of change will be much slower. The capacitor has about zero charge when the contacts are closed, current flows into the capacitor starting the same instant that the contacts open.
Perhaps somebody else can explain that more clearly.