w_tom wrote:
Ray Roberts wrote:
Most commonly damaged are appliances that connect to telephone lines
because telco routinely earths a 'whole house' protector for every
subscriber - installed for free. Incoming on AC electric. Through
modem, portable telephone base station, or fax machine. Outgoing to
earth ground via telephone line. Many instead assume this is a surge
that enters via phone line. Fine. But then what was an outgoing path
to earth? No outgoing path means no electricity - no damage. Why did
the transient not take a shorter earthing path via a telco 'installed
for free' protector?

Current flows in a complete circuit--direction is arbitrary and
irrelevant. What actually happens in many cases of applicance damage is
not voltage surges, it's ground potential difference. If your power,
telephone, cable TV and water services do not enter at the same point
and have common grounding, they can have different "gound" potentials
relative to each other. Even if lightning does not strike your house
directly, it disturbs the ground potential for a large area. This is
why telephones, televisions and refrigerators with ice makers are often
damaged--they are connected to two different systems.