Contact Dwell is the difference, in AT, between the closing of the NO contact and the opening of the NC contact for Form C contacts. It is also the difference, in AT, between the opening of the NC contact and the closing of the NO contact, for Form D contacts.
In other words, an increased or decreased magnetic field is required to make the armature or common reed move from the normally open contact to the normally closed one, or vice-versa.
