Three phases and two wires connected to the board casing: where is the ground?

Hello! If we are talking about an interfloor panel, then there is nothing easier than calling the UK, where they will tell you what kind of grounding system is in this house, etc., etc. The presence of 5 wires may not always mean tn-c-s. In the past, there could be a zero break, as an example, and was laid with a separate wire. This is an example.

Also, you need to know exactly where your electrical panel is powered from and whether there is a division of the PEN conductor into a protective zero and a working zero. Five cores - this is the TN-C-S grounding system, you need to make sure of this and install separate buses for zero working and zero protective.

PUE 1.7.135. When the zero working and zero protective conductors are separated, starting from any point of the electrical installation, it is not allowed to combine them behind this point along the energy distribution. At the point where the PEN conductor is divided into zero protective and zero working conductors, it is necessary to provide separate clamps or busbars for the conductors, connected to each other. The PEN-conductor of the supply line must be connected to the terminal or the busbar of the neutral protective PE-conductor.