Re: Lightning Damage

Lightning rods containing radioactive materials are called Early
Streamer Emmission (ESE) - a technology even discredited by the NFPA.
Lightning is not stopped, blocked, absorbed, or discharged. Lightning
will create an electrically shortest path to earthborne charges. That
shortest path previously demonstrated by up a cow's hind legs and down
via fore legs - the 'dead cow' example.

Military is even more blunt about ESE (dissipator) technology. From
a 1998 Air Force Instruction 32-1065:
14.1. General. Systems must comply with NFPA 780 and AFM 88-9,...
Early streamer emission systems or charge dissipation systems are
not permitted.

So that lightning does not find a short path to earth via
electronics, a 'whole house' protector makes a 'less than 10 foot'
connection to earth. That 'ten foot' necessary to make the earthing
connection significantly shorter than paths via electronics. So that a
lightning rod is effective, its connection to earth also must be as
short as possible. IOW if a rod is 30 feet above earth, then its
connection to earth must be significantly more conductive (electrically
shorter) than 30 feet of building (and yes, wood is an electrical
conductor).

Why worry about short conductors? The electric current called
lightning is RF electricity. Not just RF fields. Electricity is most
destructive. Wire impedance means even splices, sharp bends, wires
inside conduit, etc all adversely affect that path to earth.
Electricians who are trained in concepts of wire resistance are
therefore not familiar with wire impedance and RF nature of lightning.
What is sufficient for human safety (low resistance earthing) must be
enhanced for transistor safety (low impedance earthing).

Dan discusses a 70 degree cone of protection. Other industry
professionals define it as 60 degrees. Same concept.

If lightning finds a shorter path to earth via something outside of
that 'cone of protection', then lightning will take that path. There
is no ' "drain the field" preventing or diminishing the strike
intensity." ' Will radioactive rods (ESE) discharge something miles
above? Of course not. Lightning makes a connection to earth borne
charges. Either lightning takes a shorter path via Franklin rods or
'whole house' protector to single point earthing OR lightning takes a
destructive path via building or household electronics. Lightning
builds an electrical conductor - plasma - then discharges the cloud
electrically through that conductor. ESE devices do nothing to stop
that connection.

Wire antenna protection would be same wire found atop long distance
electric transmission towers. This 'catenary' (also called overhead
ground wire) connects lightning to earth so that lightning does not
strike any of three lower AC electric wires; a 'cone of protection'
beneath that catenary. A catenary provides protection similar to
Franklin's air terminal. The term 'counterpoise' comes from same
transmission line protection system - how that tower is earthed. I
believe counterpoise was defined first in a 1929 Westinghouse paper.

Dr Uman from U of Florida has long been considered a pioneer in
lightning protection. For example when a demonstration ESE device was
literally blown off an experiemental FAA building within days of
installation, I believe Dr Uman analyzed that failure. Other papers
such as Dr Mousa in IEEE Transactions on Power Delivery on 4 October
1998 entitled "Applicablity of Lightning Elminiation Devices to
Substatons and Power Lines" states:
... the suggestion that lightning can be eliminated has been
soundly rejected by the scientific community base on an
evaluation which was quite rigourous.
Dr Mousa then provides figures of those unacceptable ESE devices in a
paper that defines effective protection methods. Dr Mousa then states:
5. Charge dissipators will have no effect whatsoever on the frequency
of lightning strikes to substations and transmision towers ...

Dan also notes a widely discussed NM experiment that demonstrated
blunt lightning rods were more effective than pointed rods. Dissipative
(ESE) devices were not tested. Meanwhile, both pointed and blunt air
terminals remain only as reliable as their earthing. A simple earthing
electrode massively increases effectiveness. Then earthing is
significantly enlarged for an even lesser earthing improvement. High
reliability facilities and AC electric substations would typically
start construction with a massive earthing mesh. This for two reasons:
to make earthing as conductive as possible AND to create equipotential.
Earthing installed when construction first begins.

Direct strikes rarely exist at and above 200,000 amps. Majority of
strikes are 25,000 amps or less. A lurker may never experience a
200,000 amp lightning strike. Therefore household protection minimally
at 50,000 amps, and further enhanced by utility provided protection,
would withstand most every direct strike without damage or degradation
for 10+ years. A life expectancy number that can vary based upon
neighborhood and regional conditions. Such protector costs maybe $1
per protected appliance.

Residential protection is not sufficient for high tech and high
reliability facilities such as telephone switching stations, commerical
broadcasting, and observatories. Therefore significant earthing must
be installed even as footings are poured. Again, concepts of
conductivity and equipotential are addressed when architect plans are
first concieved. Such solutions make GPR irrelevant. If not
installed, then at minimum, the facility requires a kludge enhancement
- halo ground or equivalent. Such facilities may even include
surrounding chaiin link fence into the earthing system.

Earthing to protect FL homes is demonstrated in pictures at:
http://members.aol.com/gfretwell/ufer.jpg
This is only residential protection. What's in your house?

We still don't do this for every home. Yet this and more was
standard where lightning damage was not acceptable in telephone
switching stations - even multiple generations before transistors
appeared. The technology is that well proven.

All solutions are dependent on diverting lightning into paths to
earth that are not destructive. That means a single point earth ground
- minimally an earthing electrode, or an Ufer ground, or a massive mesh
network. Ufer grounds developed originally for and so effective that
direct lightning strikes would even avert munition explosions. Bonding
to earth, as previously demonstrated in FL Orange Country Emergency
Response facilities, curtailed all future damage from lightning -
direct and nearby. Earthing being the most critical component in any
protection system as even demosntrated in 1920s GE and Westinghouse
papers.

Without such earthing, then facility electronics may be damaged even
by a nearby strike as demonstrated by the 'dead cow' example and by
application note from a highly regarded industry benchmark:
http://www.polyphaser.com/ppc_TD1026.aspx

Dan Mckenna wrote:
From what I gathered, Lightning is not DC where you worry about the
resistance but a complex waveform that requires a low inductance and is
treated as a R.F. problem. Some of the early work on lightning
protection came from measuring the rise time on strikes to the Empire
State Building with low bandwidth cathode ray tube oscilloscopes. This
lead to an underestimation of the current rise times and standards that
did not go far enough in specifying very low inductance paths.

In a metal building lightning rods may not offer additional protection
as the building itself is the lowest impedance structure. For a wooden
building you want to control the attachment point and a rod is used to
do this. One talk I went to on the statistics of lightning strikes in
Tucson presented a strike density plot that had a correlation length of
50 meters. The speaker concluded that even with a structure high enough
to exceed the 70 degree "protection cone" you still had a chance for a
direct strike 50 meters away from the structure. A solar telescope on
Kitt Peak uses a wire antenna that creates a protection perimeter as is
used to protect fuel storage tanks. The grounds I have used are two
types, wet grid... a mesh that is spread out with a watering system
or a set of radial grounds as high frequency current are subject to the
skin effect and a lower impedance is obtained with multiple grounds
designed a a counterpoise like used in high power low frequency
transmitting antennas.

A class of expensive fancy rods known a dissipative system some times
used radioactive sources or many fine points to "drain the field"
preventing or diminishing the strike intensity. A series of tests
debunked this class of devices and demonstrated no advantage over a
blunt rod. (New Mexico Tech ?) The E field of a thunder storm is
centered many thousands if not 10s of thousand feet in altitude and it
seems not to care about the details of the attachment. The path
inductance and current density in the grounding system does however
effect the peak voltages induced into the structure and can cause
secondary breakdowns if the impedance is two high. In addition large
strikes e.g. 250,000 amps will generate secondary discharges off of high
field regions caused by corners which cause large field gradients and
rods at the corners of a structure help to control the current path even
though they are "only" 10s of amps.

All of this is covered in the Lightning book by Uman (sp?)

.

Relevant Pages

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