The letter “L” on a socket stands for “Line” and indicates which pin of the socket is connected to the phase wire or the live wire. In the Netherlands, the letter “L” is used to indicate the phase wire, which carries the electrical voltage. The phase wire is usually brown in color.

It is important to know which pin or connection in the socket corresponds to the letter “L” to ensure the correct connection is used when connecting electrical devices. The other pins or connections in the socket are usually reserved for the neutral wire (indicated with “N”) and the grounding wire (indicated with “PE” or a grounding symbol).

However, it is always advisable to exercise caution when dealing with electricity and to consult a qualified electrician if you are unsure about the correct connection or use of a socket.