What is slow action?

SPST-NC + SPST-NO Contact (Slow Action) Example

SPST-NC + SPST-NO contact slow action has a direct opening mechanism (forcibly opened contacts) defined under EN 60497-5-1. The NC contact side is the only side with a direct opening mechanism (forcibly opened contacts). 
When contact welding occur, a plunger is pushed down to open the NC contacts and break the circuit.

DPST-NC Contact (Slow Action) Example

DPST-NC contact slow action has a direct opening mechanism (forcibly opened contacts) defined under EN60497-5-1. Both NC contact sides have a direct opening mechanism (forcibly opened contacts).