Source google image: https://upload.wikimedia.org/wikipedia/commons/6/68/Extrait_sch%C3%A9ma_%C3%A9lectrique_prs.png
Schema electrique signalisation
Source google image: https://upload.wikimedia.org/wikipedia/commons/6/68/Extrait_sch%C3%A9ma_%C3%A9lectrique_prs.png