The relay is the first device in the panel that “thinks”: a small coil that pulls in contacts. With it you'll build the most important circuit in all of classic control: self-holding (Start/Stop with two buttons), and then the interlock between two devices. Each device: a definition, its look and symbol, a simulation, hands-on wiring, and 3 questions.
Symbols according to IEC 60617 and NEMA ICS 19. Relay terminal numbers according to IEC 60947-5-1: the coil is A1-A2, and a changeover (CO) contact is 11 common, 12 NC, 14 NO (then 21-22-24, 31-32-34…). Pin numbers (1…8, 1…11, 1…14) vary between manufacturers, so check the diagram printed on the relay or socket in your hand.
© 2026 LearnElectricals. All rights reserved. This site is not affiliated with any of the companies mentioned (such as Siemens, Allen-Bradley, Delta, Schneider and others); names and trademarks belong to their owners and are used only to explain the devices.