Echelon LONWORKS PLT-22, User Manual

Page: 39 / 128

PL Transmitter
PL Receiver
Power Line
(AC Mains)
Figure 4.3 Basic Mains Coupling Circuit
A key factor affecting the type of mains coupling circuit to be used is the wiring style
of the power distribution system to which the coupling circuit will be connected.
Wiring topologies vary from application to application, e.g., homes versus commercial
buildings, as well as from country to country. Even so, wiring styles can be divided
into two major categories: wiring systems where a separate earth conductor is
present and accessible (i.e., safety ground, which is not the same as a neutral wire
with an earth bond), and wiring systems where there is no earth conductor.
When earth is always present, a coupling method known as line-to-earth coupling is
preferred. In line-to-earth coupling the communications signal is coupled to the line
wire relative to earth, and earth is used as the communications signal return path.
This coupling technique is also referred to as earth-return coupling. Local restrictions
may apply to the use of line-to-earth coupling; see Ground Leakage Currents later in
this chapter.
A simple example of a line-to-earth coupling circuit is shown in figure 4.4.
L
ON
W
ORKS
PLT-22 Transceiver User’s Guide 4-5