What has worked well for me (and, FWIW, is the way the LPB couplers that have recently appeared on eBay have been pre-wired, and someone's handwritten notes with my Radio Systems one indicate) is, using a standard 15-amp, 120-volt, three-prong plug and wiring the ground prong to the coupler terminal marked 'neutral' and the two flat prongs (hot and neutral) to two of the 'hot' terminals of the coupler.
Notes on grounds and neutrals: While neutral will be connected to ground at some point in a building's wiring system (usually at the breaker box) and will appear to be a short circuit at DC ond low frequency AC, at radio frequencies this will NOT necessarily be a short circuit. In fact, there is a method of loading a tower as an antenna where the tower is NOT insulated from ground, and is fed at a point along its length which presents the correct impedance at the desired operationg frequency. This is called "Shunt Loading".
Also, with Carrier Current, the object is to cause RF current to flow in the wires, creating a magentic field in close proximity to the wiring (contrast with a conventional antenna, where the goal is to project an electrical wave at as great a distance as possible). This can actually be demonstrated with a common portable radio (which uses a ferrite 'loopstick' antenna).
When receiving a "normal" radio station, you've probably noticed that reception varies depending on orientation of the radio, with best reception achieved when the front or back of the radio is oriented toward the direction of the transmitter, and is weakest (and can often be nearly fully nulled) when the end of the radio (and hence it's antenna) is pointing at the station.
With a carrier current station, the primary mode of transmission is via magnetic wave, and therefore, within a few hundred feet of the "antenna" (power line) you will notice that the radio's orientation is opposite that of a "normal" station: orienting the radio so the end points toward the signal offers the best reception, with minimum reception happening when the the front or back of the radio faces the signal source.
I have experienced this with my own station, and can, in fact, observe that at a far enough distance, with a very good radio, when I get beyond the range of the magnetic, or induced field, I can still receive the electrical, or radiated signal, but must rotate the receiver 90 degrees to do so.
So now you know how to tell if you are receiving a magnetic or electrical wave 🙂
While FM stations can state that they are broadcasting "horizontally and vertically," the dual AM Part 15 Station, using carrier current and 3-meter antenna, can proudly say: "Broadcasting magnetically and electrically!"