On 9/6/2018 8:46 AM, Gareth's Downstairs Computer wrote:
On 06/09/2018 13:59, Rambo wrote:
On Thu, 6 Sep 2018 11:46:55 +0100, Gareth's Downstairs Computer
wrote:

Unearthed the previous fan of plumbers' copper microbore tubes
and associated ground rod to find a corroded and non conductive
mess and raised the question of how to protect underground
junctions from the worst that nature could throw at them?

Firstly, resurrecting a technique from school metalwork lessons
from 53 years ago when brazing things together, dig out the
gas torch, soldering flux***** and solder and connect all together
electrically.

Secondly, to protect the now-relatively-massive joint, smear with
petroleum grease. Was this a good idea, and is there something better?

***** Curious as to whether could be combined with one's radio
interest to nake a flux capacitor to go time travellingg :-)


cathodic protection?


Interesting because between the house TT earth, a steel rod and the
copper RF earth is now about 0.4 volts, making the ohmmeter go haywire
trying to measure the resistance between them.

Yet another ground to contend with is whatever may come with a cable TV
connection. (Sorry for my ignorance, I am not sure how to translate for
the other side of the Atlantic! In the US we typically have a 75 ohm
coax coming in for this purpose.) At another residence I had about 3
volts between that ground and the ground for AC power. When I connected
the coax to an FM tuner in the music system, to play an FM station that
was carried at baseband, that put 3 volts between the tuner's antenna
connection and its power connection (until I eventually put in some
isolation...) There was a lot of hum out of the system with a 300 watt
audio amp feeding the speakers!
Bob Wilson, WA9D

In article , says...

Yet another ground to contend with is whatever may come with a cable TV
connection. (Sorry for my ignorance, I am not sure how to translate for
the other side of the Atlantic! In the US we typically have a 75 ohm
coax coming in for this purpose.) At another residence I had about 3
volts between that ground and the ground for AC power. When I connected
the coax to an FM tuner in the music system, to play an FM station that
was carried at baseband, that put 3 volts between the tuner's antenna
connection and its power connection (until I eventually put in some
isolation...) There was a lot of hum out of the system with a 300 watt
audio amp feeding the speakers!
Bob Wilson, WA9D



All ground rods and other earth grounds have to be bonded together or
you have no real ground system.

That is you can not have a ground rod on one side of the house connected
to something and another ground rod on the other side of the house
connected to other equipment unless you run a bonding wire between the
two.

On 09/09/2018 22:43, Ralph Mowery wrote:
In article , says...

Yet another ground to contend with is whatever may come with a cable TV
connection. (Sorry for my ignorance, I am not sure how to translate for
the other side of the Atlantic! In the US we typically have a 75 ohm
coax coming in for this purpose.) At another residence I had about 3
volts between that ground and the ground for AC power. When I connected
the coax to an FM tuner in the music system, to play an FM station that
was carried at baseband, that put 3 volts between the tuner's antenna
connection and its power connection (until I eventually put in some
isolation...) There was a lot of hum out of the system with a 300 watt
audio amp feeding the speakers!
Bob Wilson, WA9D



All ground rods and other earth grounds have to be bonded together or
you have no real ground system.

That is you can not have a ground rod on one side of the house connected
to something and another ground rod on the other side of the house
connected to other equipment unless you run a bonding wire between the
two.



I offer the example of an outhouse in a PME supplied household where the
PME earth must not be exported to the outhouse where a separate TT
earth rod, not bonded to that of the house must be supplied.

On 09/09/2018 22:32, Bob Wilson wrote:
... There was a lot of hum out of the system with a 300 watt
audio amp feeding the speakers!


Somewhat reminiscent of the opening sequence in
one of the Back To The Future films!

Or, going back some years to the April Edition
of Wireless World and the article by the
Dutchly-named George Izzard O'Veering.

Bob Wilson wrote:
Yet another ground to contend with is whatever may come with a cable TV
connection. (Sorry for my ignorance, I am not sure how to translate for
the other side of the Atlantic! In the US we typically have a 75 ohm
coax coming in for this purpose.) At another residence I had about 3
volts between that ground and the ground for AC power.

A modern cable TV demarcation point has galvanic isolation.
With a TV there usually is no problem because it usually has galvanic
isolation in its input circuit as well (some ferrite bead transformer
between the input and the tuner).

For radio tuners that may be different.