How to divide three-phase four-wire sockets?

The power socket with four jacks is three-phase and four-wire, which is easy to distinguish; The top electrode is the grounding electrode, and the other three are the A-phase, B-phase and C-phase power supplies.

The socket with two jacks is a single-phase power socket;

There are two kinds of three-jack sockets: one is a single-phase power socket with grounding electrode, and the other is a three-phase socket without grounding electrode.