The ARRL site, http://www.arrl.org/tis/info/HTML/plc/#Field , provides
links to the following information:

"PLC is a "carrier-current" system, designed to intentionally conduct
signals using electrical wiring. Although a carrier-current device is an
unintentional emitter, because the power lines have such a significant
potential to radiate and because a practical carrier-current device
generally needs more signal than the permitted conducted emissions
levels for unintentional emitters, carrier-current devices are not
required to meet those conducted-emissions limits, but are required to
meet the general radiated emissions limits in Sec. 15.209.

§ 15.209 states that the radiated emission limits of intentional
radiators generally can't exceed the field strength levels specified in
the following table:

Frequency (MHz) Field Strength (microvolts/meter @meters)

0.009-0.490 2400/F(kHz) 300

0.490-1.705 24000/F(kHz) 30

1.705-30.0 30 30

30-88 100 3

88-216 150 3

216-960 200 3

Above 960 500 3

Carrier-current devices are "Verified" as described in the Part-15
rules. This means that the manufacturer is required to test them to
ensure that they comply with the FCC regulations. Under the present
rules, they must be tested at 3 typical locations. "

Note that the HF Spectrum allows a S8 to S9 signal level, 30 uV/m at 30
meters distance.