🚀 go-pugleaf

Sorry, but...

>Modems are rarely damaged by phone line surges.

Not so - modems are **often** damaged...etc

>Modems even have galvanic isolation that separates modem for phone line.

They'll either have a fusible transformer that 'sacrifices' itself in the
event of a surge in order to protect the PC, or an optical coupling that
sort of does the same thing.

But modems have a
> direct connection to one AC mains electric wire.
>

Nope - full isolation via the power adaptor (so-called 'double insulated' if
in a plastic case). If internal to a PC, the only power connections with be
to the DC power bus. There should be no circuit path between the AC input
and the low-voltage DC side unless an auto-transformer has been used -
highly unlikely.

>   Surges must first form a complete electrical circuit.  >Current passes
completely through everything in that circuit.  Only then does one part of
that circuit fail - become surge damaged.

In the event of a lightning strike or phone line surge caused by a distant
strike, 'circuits' will include air paths due to the high potential
difference ('voltage' if you must) of the surge. Simply having the kit on a
surface that has a low-to-high resistance path to earth (ie a table with
metals legs or a nearby metal desk lamp or grounded PC case) may form a
circuit. Also remember that nearby/direct lighting strikes can contain
high-frequency components that will drive voltage through insulation.

>   Telephone lines already have effective surge protector.

Not for a major surge.

> Phones that do not connect to AC mains are typically
> not damaged by such surges.

Sorry, not so. HF components and EMP-induced currents can fry kit in the
vicinity even if there's no direct connection to anything. - a mobile phone
left in the middle of a desk can be fried by a nearby lightning strike.

NK