Wikipedia
Perilex is the tradename for an approved indoor three-phase electric power connector system used in Germany ( West Germany), the Netherlands and Sweden. It has mostly been superseded by the IEC 60309 system used throughout Europe.
There are two variants, a more common 16-ampere version and a rarely used, 25-ampere version. The connectors are equipped with protective earth (PE), a neutral conductor (N) and three phase conductors (L1, L2, L3; formerly: R, S, T). As the German industrial norm VDE 0100 prescribed the phase sequence for all types of three-phase connectors in a way incompatible with the original Perilex pinout, the R and T connectors may have been swapped. The PE connector is protruding and will therefore mate first. In order to distinguish the variants, the 16-ampere version has a horizontal PE connector, whereas it is vertical in the 25-ampere variant.
In Germany, Perilex connectors have been standardised by DIN. The 16-ampere version is DIN 49445 (socket) and DIN 49446 (plug) and the 25-ampere version is DIN 49447 (socket) and DIN 49448 (plug). It did replace an earlier flat 4-pin connector (3 phases and neutral) that was standardized in DIN 49450 / DIN 49451. The earlier flat connector did continue to exist in East Germany - after German reunification, all machinery was required to be rebuilt to round connectors until 1998.
Usage of the Perilex connectors is usually confined to small businesses (e.g. bakeries, restaurants), medical facilities (hospitals, laboratories) and homes, where it has the advantage of a smaller form factor and better cleanability. However, at construction sites and industrial facilities, the IEC connectors are preferred due to their better robustness and due to being approved for medium-term outdoor use. Furthermore, it is unwise to connect three-phase electrical motors to Perilex sockets due to the afore-mentioned ambiguity regarding the phase sequence. Since 1 January 1975, the use of the Perilex system has been outlawed in Germany for new industrial installations but continues to be legal in homes, hospitals and small businesses. However, even there, it is being superseded by the IEC 60309 system used throughout Europe. The fact that East Germany used a completely different system ( TGL 4176), resulting in two incompatible non-IEC systems in re-unified Germany, also contributes to this trend.