In the RFI/EMI world the maximum length
of grounding conductors has been found
to be 1/20 of a wavelength. Conductors
longer then 1/20 of a wavelength become
effective unintentional radiators. It is true
that we consider a 1/4 wavelength to be
the most effective and desirable length.
But significant radiation does occur from
even cables as short as 1/20 WL.

In the typical installation even shorter conductors
can become electrically longer due to the bends
a normal conductor experiences. Very few, if any,
real world grounding conductors run in a straight
line. And the typical grounding conductor in a residence
is anything but short and straight. Each bend adds
inductance that increases the electrical length of
a conductor.

Ignoring bends, for various frequencies, 1.20 of a
wave length equates to:
100KHz 150M
500KHz ï€*ï€* 30M
1MHz ï€* 15M
5MHz 0.ï€*3M
10MHz 0.15M
15MHz ï€* 1.0M
20MHz ï€*0.75M

For RFI with frequencies at 5MHz and higher it should be
clear that it is very easy to exceed the magic "1/20�" rule.

This is why efforts to reduce Differential Mode noise must
be applied as close to the noise source as possible.

Other thing to keep in mind that in the normal residence, by NEC,
the ground and neutral are bonded at the meter base, but the house
grounds are bonded to each other in the breaker box and may be
bonded to each other at other points. This creates an wiring maze
that defies any thorough analysis. Grounding conductors can form
an unbelievably effective antenna! This was experienced during a test
at a wired new home that was not connected to any power sources.
In the bedrooms furthest from the breaker box, attaching any of the
power conductors to the antenna connector on a DX398 and battery
powered R2000 proved to be a learning experience. A ground wire
that is an effective antenna will certainly radiate RF noise
effectively.

The house grounds were connected to what the NEC would recognize
as a "meter base" even though the home will operate from a PV array
with a propane powered back up genset. The exterior grounds are much
better then what the NEC calls for.

Terry