"m II" wrote
Jack Painter wrote:
"m II" wrote
CaveDweller wrote:

Of course, I'm interested in the lowest noise possible, but my main
concern is protecting my new baby.

This is a nice, simple solution. I had to go back in time to find it for
you.

http://www.gutenberg.net/cdproject/c...ah/fig006c.png

mike

NO!

That drawing, taken on it's own, will allow a nearby strike to blow your
radio into pieces so fine you can clean up with a duster. Why? Becasue
the
electric power ground (house entrance), and cold water ground (a
different
entrance than AC service 99% of the time), and that phony knife-switch
"protector" ground rod, are all at different locations and will have
*enormous* electrical potential between them .


I disagree. A big knife switch will have a few INCHES of air gap between
the common and the radio feed. At roughly 20K volts per inch needed to
jump the gap to the disconnected radio, any few volt difference between
grounding potentials is immaterial.

Check the diagram. The radio is **never** connected to the ground rod.
It's only meant to discharge antenna static to ground

Also, this switch is an ISOLATING switch and not meant in any case to
supplant a proper lightning protection set up.


A metal cold water line coming into the house is the PREFERRED code
ground for the house (system) wiring. An artificial electrode like a
ground rod/plate may be used if plastic line is coming in for the water,
but NOT if metal water line is available.

To make you even more paranoid, the electrical code, at least here, says
the ground rod/pipe may NOT have a resistance greater than TEN ohms
between it and ground. Up to ten ohms is code acceptable.

That means on a nominal 120 volt residential circuit, a fault current of
up to TWELVE amps may be flowing at all times and not even trip the
breaker.

mike


Hi Mike,

You are very confused about this, and I will try to correct your
misunderstandings.

1. The dwg at
http://www.gutenberg.net/cdproject/c...ah/fig006c.png allows a
path for lightning to the radio at all times, whether the radio is connected
to AC at the time or not. I warned readers that such simple fixes were
dangerous and improper, specifically because such dwgs do not show or
explain that there is a connection via the knife-switch ground, AC ground
and that cold water ground that could have disasterous effects in the event
of a nearby strike. It's also clear that you don't understand how those
paths exist, but presumably you are in this discussion to learn something.

2. Cold water line is not authorized as AC service entrance ground, and a
second ground may never be made to it under any circumstances without
bonding of all systems. Older homes that used cold water ground remain legal
unless modified or upgraded to comply with current code.

But....
When a homeowner connects an external antenna to a radio inside the home,
many electrical principals, code requirements and lightning protection
issues come into play that were not a concern beforehand. When you are
dealing with 100Mv potential from cloud to ground, it is totally immaterial
what you think you know about 20Kv potentials. Now, DC resistance of a
system is almost meaningless, and the inductive effects prevail. Separation
of unbonded systems should be a minumum of 3 feet, not fractions of an inch
as would suffice for 120/240v fault protection. Most lighning protection
designs account for the most probable condition of indirect nearby strikes,
in which the ground will raise from 0v to several hundred thousand volts.
Every part of a home and station's connection to ground will be connected to
part of this potential, and the differential voltages across unbonded
systems are absolutely explosive in such cases.

You were not exposed to such risk before you strung up or erected antennas
in the air and made grounding connections at different places such as your
RF radio ground, outside antenna ground, coax shield at the radio case, and
AC ground from the radio case to your home wiring. When you add a cold water
ground to the mix you increase the potential for damage even more. This is
why electrical bonding of all systems is so critical, and that bonding must
be of extremely low impedance (not just DC resistance!) to maintain the
lowest possible potential between all parts of the grounding system.

You did make one comment that was accurate, and that was the importance of
disconnecting the system to protect it. For the most basic kinds of hobby
listening, tossing the antenna feedline out the window and unplugging the
radio long before a thunderstorm arrives will be suffcient. But making any
kind of ground connection (be it cold water, under-house, external RF
ground, etc) let the user beware! They must disconnect all connections that
are not a permanent, bonded connections designed to withstand the extremely
high potentials from nearby lightning strikes.

The earth is the final destination of all lightning, and all lightning
rasies earth-ground potential to voltages no home wiring was designed or is
capable of handling. Bonding is what prevents our systems from having to
carry current that would violently and completely destroy it. Current only
flows when differences of potential (voltage) occur. Is this making things
a little clearer?

Best regards,

Jack