The difference in voltage between the two will cause a current
flow between them in the only path they can find which is your
house wiring. This is enough to cause serious damage to your wiring
including starting fires.
Something like this happened to us a few years back. During a
thunderstorm, we smelled smoke in the house -- the acrid kind that's
like ozone. It was highest in the area under the stair near the well
I think the breaker flipped; I don't remember. Maybe we flipped it
or shut off the main. (I'm the daughter of a long line of electrical
contractors; checking breakers is in my blood. ) There appeared to
be no other action to take, as no fire was apparent. (We do have
a/b/c fire extinguishers throughout the house.) We checked that area
repeatedly for hours after, as smoldering fires can go on and on
unnoticed if they get into a big house beam.
A heads-up was that we had electric power but no water pressure. The
electrical wiring from the retaining tank runs out to our well 50
Next day, we went outside to examine the wellhead. I was expecting
to see melted metal. No apparent damage! Nor to nearby trees, utility
pole, house, roof, chimneys, etc. (Though trees hit by lightning can
appear mostly normal for a year or two before they finally die.) No
aroma of burning.
Nonetheless, the well pump AND ALL OF THE UNDERGROUND WIRING between
well and house had to be replaced. A colossal inconvenience that
could have been a tragedy.
My best guess, as we live in the woods, is that lightning hit a
nearby tree, traveled down, and "jumped" to the 300-foot-deep metal
shaft that houses our well-water line and the housing for its wiring.
I presume they acted as the main grounding mechanism. I'm guessing
that the metal housing for the well wiring was the conduit to the
house. Or maybe the underground water pipe, which dates to 1981 and
could well be copper.
The gentlemen who replaced our well said they hear quite often about
wells and well-wiring going kaput after a thunderstorm, with no
obvious nearby damage.