ABSTRACT
The first seven chapters of this book have discussed fixed contacts. You have explored the physical effects of two metals in contact and the effect of chemical reactions at the contact interface. By using these fundamental principles, you have been shown how it is possible to design fixed contacts for a very wide range of currents: e.g., from connectors for power circuits that pass many thousands of amperes and must survive short circuit currents of over 105A to connectors for electronic equipment that can see currents as low as 10-9A. With this chapter, you will now begin to study the equally interesting effects that occur as you separate two contacts in order to interrupt the flow of current in a circuit. For the most part, we will be concerned with currents greater than 0.1A and circuit voltages greater than a few volts. The range of currents and voltages will be discussed in detail later in this chapter. This range of course covers a vast array of switching devices from small a.c. and d.c. relays and switches to large circuit breakers that interrupt high-power circuits.
