Priniciples of Electromechanical Relay Operation
3.2 Direct-Current Relay Actuator Systems
A relay is a remotely controlled operated switch; it consists of one or more
contact pairs that serve to open, close or transfer external circuits.
Consideration of the electrical phenomena occurring at the coils during the
switching function is given in Paragraph 3.13, and contact(s) considerations
start at Paragraph 3.14. Some mechanical requirements for their operation must
be considered first.