w_tom wrote:
On Jul 14, 5:36 am, Caesar Romano wrote:
I don't know. How is the quality of an "earthing" determined or
measured?

..
The NIST guide cites US insurance information that indicates equipment
most likely to be damaged by lightning is computers with modem
connection and TV/related equipment - presumably with cable connection.
All can be damaged by high voltage between signal and power wires.

If a surge comes in on power wires and produces 1000A to earth through a
very good 10 ohm impedance to earth, the 'ground' at the service panel
rises 10,000V above 'absolute' ground potential. Equipment connected
only to power can float above 'absolute' ground. The only way to protect
equipment with both power and phone/cable connection is to make sure the
phone and cable 'ground' potential is the same as the power 'ground'.
That requires a *short* connection from phone/cable entrance protectors
to the power system 'ground'.

An example of a cable protector 'ground' wire that is too long is in the
IEEE guide starting pdf page 40.
..
If in sandy soil, other techniques include a halo (loop) ground
..
From
http://www.lightningsafety.com/nlsi_...finitions.html
"Halo Grounded Ring: A grounded No. 2 wire, installed around all four
walls inside a small building, at an elevation of approx. six inches
below the ceiling. They are used around transmitter equipment."
Perhaps w_ could learn the right name (ground ring).
..
Ufer grounding means surge protection is installed when footings are
poured - not when the electrician arrives to install wires.
..
Ufer grounds are required for most new construction, and are good ground
electrodes.
..
Meanwhile
a utility offers suggestions on how to fix defectively installed
earthing:
http://www.cinergy.com/surge/ttip08.htm
That buried interconnection wire converts multiple earthing electrodes
into single point earth ground while increasing conductivity.
..
The buried interconnection wire (Figure 2 "right") is unlikely to keep
power/phone/cable grounds at the same potential.
Figure 2 "preferred" is correct.
..
all ground wire routed separately to meet at
the earthing electrode (single point earth ground).
..
Running phone and cable 'ground' wires to the earthing electrode will
almost certainly make the power-signal interconnection distance longer,
increasing the voltage between power/phone/cable wires.

The author of the NIST guide has written "the impedance of the grounding
system to ‘true earth’ is far less important than the integrity of the
bonding of the various parts of the grounding system."

Often the phone or cable entry protectors are distant from the power
service. In that case the IEEE guide says "the only effective way of
protecting the equipment is to use a multiport [plug-in] protector."
..
Ham radio
operators who learned this stuff will install better earthing systems:
..
Ham radio operators are likely to have a direct lightning strike on
their antennas. Surge amps are far higher than can be conducted in on
power/cable/phone wires. For protection from a direct strike you need
lightning rods.

--
bud--