UNE 20004-4/1C:1976
SIMBOLOS (LITERALES Y GRAFICOS) Y ESQUEMAS EN ELECTROTECNIA. CONTACTOS, APARAMENTA, MANDOS MECANICOS, ARRANCADORES Y RELES ELECTROMECANICOS
RECOMMENDED GRAPHICAL SYMBOLS: CONTACTS, SWITCHGEAR, MECHANICAL CONTROLS STARTERS AND ELEMENTS OF ELECTROMECHANICAL RELAYS