Have you never static shocked a radio antenna? Why was that radio
not damaged by up to 18,000 volts? Radios have internal protection
which is why those 10,000+ volts did not damage. Parameters are
voltage ... and time.

Reason why a well earthed protection 'system' protect electronics
even from direct strikes includes internal electronics protection, fast
response of all protectors, and how well a protection system is
earthed. With properly earthed protection, then protection internal to
electronics is not overwhelmed; damage does not occur.

Disconnecting without earthing is not a best protection method. Ham
radio operators in the early days would disconnect an antenna lead, put
that connector inside a mason jar, and still suffer damage. When that
antenna lead was earthed, then damage stopped. Disconnecting - trying
to stop a destructive transient - works when the transient has a better
path to earth. Most essential is to provide a better path to earth.
Disconnecting would only enhance a good protection system. But
disconnecting without a non-destructive path to earth has been
demonstrated not sufficient. Idea is to keep protection inside that
electronics from not being overwhelmed even by a direct lightning
strike.

What was more than sufficient to protect telephone switching stations
- connected to overhead wires everywhere in town? Gas discharge tubes.
We have since obsoleted that technology (depending on other
parameters) twice over. But response of a gas discharge tube is not
'too slow'. Too often, people will blame 'slow GDT' for damage when
they failed to confirm the most critical component in a protection
system - earth ground and connections to that earthing 'system'.

Robert11 wrote:
Very interesting comments on my question of a few days ago re lightning
arrestors.
Thank you all for trying to educate me on this subject; really find it
confusing.
Thread is a bit buried by now, so thought I'd start another one.

I fully understand that the best approach is to (also) just disconnect
everything.

But if not around, here's what I don't understand and concerns me.

Assuming a "nearby" strike, and a subsequent emp pulse that's picked up by a
receive only antenna wire strung outside:

No matter how quickly an arrestor's gas tube fires, and diverts the pulse to
a good RF ground, the fact that it takes
a few hundred volt threshold to fire makes "any" gas tube type of arrestor
almost worthless re the protection of a receiver whose front end certainly
won't take a few hundred volts, even for u-seconds, probably.
...