blueman wrote:
If that wire is connected to the chassis ground and if that in turn is
connected to the ground prong in the plug, then it should be properly
grounded (and surge protected) in the house. If that electrical signal
is just hanging there isolated from my house wiring then there is not
much I can do about it since I can't access it...

Wire has impedance. That impedance is irrelevant to 60 Hz AC
electricity; grounding that is for human safety. That same ground wire
has too many sharp bends, splices, and bundled with other wires.
Impedance is excessively high for transient protection. Bundled with
other wires, it may even induce transients on those other wires.

Earthing for electronics protection demands other precautions such as
no wire splices, no sharp bends, not inside metallic conduit, separated
from other wires, and especially short distance. AC wall receptacle
safety ground violates principles required for earth ground.

However, when transients are earthed at a building entrance (ie the
'whole house' protector), then higher impedance of interior wiring adds
to appliance protection. This separation and impedance is why better
protected facilities put a protector at earth ground AND distant from
protected electronics.

For earthing each utility in a residential dwelling, each utility
should make a less than 10 foot earthing connection - that wire length
is critical. Therefore utilities enter a building at a common location
to have a short earthing connection to a common earthing electrode.
For earthing (and low impedance), the ground connection must be short -
and other factors.