Although the field of low-voltage power-line communications (PLC) has been maturing over the past few decades, the effective, economic and safe coupling of a modem to the live power grid remains a challenging topic. In literature, PLC coupling is covered sparsely, compared to other relevant PLC topics, and limited information is available to PLC researchers and designers. Therefore, this paper aims to achieve the following goals: (i) to guide the reader to a practical understanding of PLC coupling concepts; (ii) to expose the reader to a wide range of low-voltage PLC couplers and their operating principles; (iii) to brief the reader on typical PLC coupler design steps for the various classes of couplers; (iv) to establish good safety principles for these couplers; and (v) to assist researchers and designers with PLC coupler selection, through a qualitative comparison of various coupler pros and cons. This comparison illustrates why the transformer-capacitor coupler remains a coupler of choice, and that the potential of inductor-capacitor (L-C) couplers is perhaps overlooked.
