Electromagnetic relays make use of the magnetic field in the core of an inductor to alter the setting of a mechanical switch. There is an overlap in the meanings of the words relay and contactor; in general a relay is a comparatively low-voltage low-current device, and a contactor is designed to deal with much higher levels of voltage, current or both.
• Contactors are not generally considered to be electronic components and therefore do not feature in this book. For details of contactor construction and use you should consult a specialized text of electrical engineering.
The essential parts of either device are a coil with a soft magnetic core, a moving armature, and a set of contacts which are actuated ...