I have some troubles finding what the triangle symbol on the following diagram could mean. It is not a diode because in other parts of the diagram, it is used where an input is expected.
The box is an electrical cabinet that contains circuit-breakers. The top one is an input and the 4 bottom one are outputs.
I guess it could mean that the ground cable is linked to the cabinet casing but I couldn't find any confirmation on that online and it seems strange.