dennis@home wrote:



The IEEE says plug-in
suppressors work primarily by clamping, not earthing.


Clamping to what?


“Grounding” in the following is “earthing” in the UK. It is not obvious
to me what the syntax is using earthing. Earthing as used in posts by w_
and me usually indicates a connection to the dirt/earth.

“Clamping” is to the common ground at the plug-in suppressor. For a TV
with cable connection, both power and cable need to go through the
suppressor. The cable shield connects to the power “earthing” wire at
the suppressor and the voltage on other wires is clamped to that point.

An illustration in the IEEE guide, starting pdf page 40, shows a
lightning induced surge hitting cable TV supply wiring. The surge
current lifts the cable TV ground reference away from the power ground
reference so cable TV leads are 10,000V different from the power. This
shows up at any TV connected to power and a cable lead, and the TV won’t
like it. A plug–in suppressor clamps the voltage on both the cable and
power wires to the ground reference at the suppressor. The voltages
reaching the TV are at a safe voltage.

According to the NIST guide, US insurance information indicates
equipment most frequently damaged by lightning is computers with a modem
connection, TVs and video recorders (presumably with cable TV
connections). All can be damaged by voltages between power and signal
ground references.

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