his question has its roots in users' experiences with low-frequency, low-bit-rate technologies such as the venerable X-10. HomePlug PLC technologies are vastly different in both frequency and speed. While X-10 operates at 120 kHz, HomePlug technology operates in the HF frequency spectrum, roughly 2 to 30 MHz. In this frequency range, capacitive coupling between phase wires is very strong. Think here of the twisted-pair wires from the transformer to the house, and more importantly, within the home going to the hot-water heater, clothes dryer, HVAC system, etc. The net result is that the bus bars in the breaker panel look like a low-impedance crossover point for the signals. The loss here is only a few dB.

Most circuit breakers present no problem to the PLC signals. Again, the amount of attenuation that circuit breakers contribute is very small compared to the dynamic range of the technology.