How do I know if I have three-phase power?

Three-phase power is recognizable by the connection, not by the outlet

You typically recognize three-phase power by how the connection looks, not by what it says on it. A standard (domestic) connection works with one phase; three-phase power works with three phases simultaneously. That difference is visible in the meter cabinet and at the outlet itself: a three-phase group has a different, more robust connection than the usual outlets and switches, and the associated plugs are round, with multiple poles, and often blue or red in color instead of the flat two-pole plug that most domestic appliances have. In the meter cabinet, such a group often stands out because it differs from the row of standard groups: a different color or shape of the connection, and sometimes a separate, distinctly marked part of the installation.

In case of doubt, checking with the installer or electrician is the most reliable way to get certainty, especially since a wrong assessment has consequences for what can safely be connected. This is relevant once equipment is added that requires high power — a charging station is a well-known example of this — because then it must be clear whether the existing connection is suitable for it or whether something needs to be adjusted. A visual assessment from the meter cabinet gives an initial impression, but the installation itself, with the cabling behind it, is what ultimately determines whether three-phase power is actually available.

What NEN 1010 stipulates about this

This classification of connections, groups and the way an installation is set up falls under NEN 1010, the standard for low-voltage installations. That standard has a legal status through the Building Decree and describes how an electrical installation — including the connections for three-phase power — should be executed. For the exact requirements for a specific situation, the standard itself, or the explanation from an installer who works with it, is the appropriate source.