Numbers in hyperbole were posted. Lightning is not the
massive destructive energy as implied. Lightning is high
power but not the high energy event so often promoted in
myths. Lightning is a current source - not a voltage source
(as was implied). From basic EE, voltage will rise as
necessary to maintain that current flow. And no, one need not
worry about using a telephone if the human has performed his
job. How a horse is killed when not even struck demonstrates
principles of single point earthing.
Why a single point ground? Same reason why horses can be
electrocuted when a nearby tree is struck. Lightning seeks
earth some 4 kilometers west. So it strikes a tree directly
below the cloud that is east of the horse. Shortest path
westward is up that horse's hind legs and down horse's fore
legs. Horse is killed because it became a good path for
lightning to flow west. Horse conducts electricity better
than earth beneath. Horse became part of an electric circuit.
Same applies to house (building) protection. If using
multiple grounds, then a transient can rise up on a left side
ground rod, find destructive paths through appliances, then
reenter earth via a right side earth ground. Concept is
demonstrated in a NIST figure that demonstrates why bad
earthing can cause fax machine damage:
http://www.epri-peac.com/tutorials/sol01tut.html
How to make a single point ground beneath the horse?
Surround the barn with a buried halo ground. Then earth
beneath the horse becomes one big single point ground -
equipotential. Horse can be killed by a concept that also
kills computers. Therefore better buildings also install halo
grounds or Ufer grounds. Earth ground - not a UPS or power
strip protector - being so important for computer hardware
(and horse) protection.
An introduction to concepts of building (and electronic)
protection is provided at:
http://www.bb-elec.com/tech_articles/dataline_surge_protection.asp
Protection from lightning is first and foremost about
earthing. Yes, even the household earth ground provides a
massive improvement in both human and transistor protection.
But for protection from rare, higher energy lightning strikes
(that you may never observe in your lifetime), utilities
install massively larger earth grounds. Major expense only
to marginally improve their earthing system - because
reliability is that critical.
Removing a building's earth ground (or connection from each
incoming utility to that single point earth ground) puts the
human (and transistors) at greater risk from lightning.
Reason to not use a phone during a thunderstorm? A human has
failed to install or has compromised the building's earthing
system. This should never happen in an EE's building.
The myth busters demonstrated what we have long understood
even before transistors were invented. Effective protection
has always been first and foremost about the essential single
point earth ground. Not about pointed verses blunt rods, not
about preventing lightning (ESE devices), not about blocking
the resulting transients, and not about miracle plug-in
protectors that will somehow absorb what miles of sky could
not. Protection has always been about shunts; diverting a
direct strike to earth ground on an electrically shorter and
non-destructive path.