Protection starts with the underlying geology. Best is a
monolithic soil of clay or loam that is damp. Worst is sand
or gravel. Also bad would be two different types of soil
where the more electrically conductive vein is far from the
single point ground. Example: they had a bathroom wall struck
twice by lightning. They installed lightning rods. The
bathroom wall was struck a third time. Lightning rods were
earthed in sand. Bathroom plumbing made a better connection
to deeper limestone. One poster in the Perennes once said he
had to sink a 150 foot ground rod to get through glacier
tailings and into more conductive soil. A rather extreme
example that demonstrates the point.
Establish the single point earth ground. For most, two
ground rods driven well below the frost line and separated by
a distance equivalent to their length is sufficient (Rods
closer tend to act as if they were the same rod). Idea is to
make this the best electrical ground on the property.
All incoming utilities first connect to this single point
ground either by direct wire connection or via a surge
protector. Unfortunately, your antenna violates the
principle. But there are alternative solutions. Three
examples - the bad, ugly, and good (left to right) - are
provided in figure 2. Concept demonstrated in figure 1. Halo
ground that connects your earth grounds together. This could
be a buried bare 4 AWG ground wire that interconnects AC
electric ground to TV antenna ground. That buried bare wire
makes all grounds equipotential as well as enhances the
connection of earth ground to earth:
http://www.cinergy.com/surge/ttip08.htm
A US government publication further discusses the single
point principle:
http://www.pueblo.gsa.gov/cic_text/h...ontractors.htm
Equipotential means earth beneath cottage appears to be the
same voltage no matter how massive the direct strike. We can
install a great earth ground. But that may not be
sufficient. So we surround the house with a halo ground or
Ufer ground to also make earth beneath building equipotential.
Homes built to contain transistors have a halo or Ufer ground
installed when footing are pours - plans for good earthing
must be started that early. This principle avoids
complications created by varying earths. A complication that
most homes new not worry about. But a halo or Ufer ground
should be installed in all new construction because it is so
cheap and so effective.
Now that we have established a good earth ground, we are now
ready to make connection to that ground. Every wire entering
the building must connect that that single point ground.
Ground wire connection (ie from neutral bus bar) must be
short, direct, and independent. IOW (short) it must be less
than ten feet. It (direct) must have no sharp bends; no
splices. (Even 90 turns and lead solder joints on copper water
pipes violate good connection requirements). It (independent)
must be separated from all other non-earthing wires and must
not connect to any other earthing wire until they all meet at
the single point ground.
Idea is to make that earthing wire low impedance; not just
low resistance. For example, 90 degree bends could add a
mircohenries to wire inductance. For earthing, that would
result in a substantial increase in wire impedance.
Using numbers: that earthing wire might have less than .1
ohms resistance. But it might also have as much as 4 ohms
impedance. Any increase in earthing wire impedance means a
surge may seek other and destructive paths to earth ground
inside the building. An earthing wire from bus bar straight
through foundation to a point just above soil would be
superior to an earth ground that routes up over top of
foundation (through 2x10 or rim board) and back down to earth.
Two other AC electric wires have also entered the building
and cannot be earthed - also called hot wires. These are the
most common source of surge damage especially to phone
appliances that use AC electric - answering machine, computer
modem, portable phone base station. The 'whole house'
protector must connect from each wire to that bus bar. One
minimally sized example sold in Home Depot is Intermatic
IG1240RC. Others have been listed in newsgroup misc.rural as
"telephone wire/lightning strikes" on 30 Sept 2003:
http://tinyurl.com/q6g6
A 'whole house' protector for residential service should be
at minimum 1000 joules and 50,000 amps. Some, such as GE's
THQLSurge (if I have remembered the name correctly) that is
also sold in Lowes, is undersized and overpriced. Square D
makes one protector that is undersized AND does not even
provide joules in its specs. But in that list is another
Square D product that is well designed - more than meets
minimum requirements.
Telco installs a 'whole house' protector that meets US
National Electrical Code requirements:
From Article 800.30A:
A listed primary protector shall be provided on each circuit
run partly or entirely in aerial wire or aerial cable not
confined within the block containing the building served so
as to be exposed to accidental contact with electric light or
power conductor operating at over 300 volts to ground. In
addition, where there exists a lightning exposure, each
interbuilding circuit on a premise shall be protected by a
listed primary protector at each end of the interbuilding
circuit.
Article 800.30B Location.
The primary protector shall be located in, on, or immediately
adjacent to the structure or building served and as close as
practical to the point of entrance.
Article 800.31
The primary protector shall consist of an arrester connected
between each line conducor and ground in an appropriate
mounting. Primary protector terminals shall be marked to
indicate line and ground as applicable.
NID that contains telephone 'whole house' protector is:
http://www.alarmsuperstore.com/bw/bw%20connectors.htm or
http://www.bass-home.com/gotoproduct.cfm?item=91598
A 14 AWG wire connects from that box to the single point
ground. Again, it should meet these criteria rather than look
neat: be short, direct, and independent. Too many telco
installers want to square off the wire or neatly ty-wrap a
ground wire to other cables. Wrong. That 14 AWG (more often
is 12 AWG) wire must run independently and directly to the
same single point ground used by AC electric. Both grounds
meet at the earthing rod - the single point ground.
Every incoming wire - all three AC electric, both telephone
wires, and shield of any incoming coax cable from satellite
dish - are earthed to same earth ground. As noted earlier,
that antenna will require special attention. Now lets discuss
induced transients.
Lightning strikes the TV antenna seeking earth ground. Path
will be destructive via household wires. And not necessary
just through TV and AC electric to earth ground. That antenna
wire may be bundled with other wires. Therefore that antenna
wire induces transients on other wires or may even arc into
those other wires.
Same problem is also created by plug-in protectors. Lets
say a plug-in protector is earthing the transient. IOW it is
shunting a transient into the AC electric safety ground wire.
But that safety ground wire is bundled with other wires. Now
a transient is induced onto those other wires. Just another
example of why plug-in protectors are not effective and can
even contribute to surge damage.
Idea is to earth a transient before it can enter the
building. Not just earth anywhere, but earth less than 10
feet to a single point. Campers demonstrate the principle.
They were sleeping nearby a tree that was struck. Lightning
strikes tree to obtain earth borne charges some kilometers
beyond those boys. Some were sleeping perpendicular to that
tree and were not hurt. Any boy who was sleeping pointed
towards that tree had electricity rise up into his feet, pass
through his body, then exit via his head. Body is more
conductive than earth. Lightning will find every conductive
path to those earth borne charges some kilometers away. This
is also why multiple earth grounds on a building can cause
lightning to find the other earth ground, destructively, via
the house.
When lightning is striking, stand with both feet together -
the single point ground. Building uses same concept to not
have appliances damaged.
Incoming transients also applies to buried wires. This
industry professional (another source of protectors)
demonstrates two structures - each with their own single point
earth ground AND both single point grounds interconnected.
Buried phone line is also carrying a destructive transient.
Phone line is earthed at building's earth ground before
entering because even buried wires carry destructive
transients:
http://www.erico.com/public/library/...es/tncr002.pdf
'Whole house' protectors are only secondary protection.
Primary protection is provided by the utility at transformer.
But that primary protector may need be inspected. Some
pictures of what to look for:
http://www.tvtower.com/fpl.html
And rules for earthing:
http://www.tvtower.com/grounding_and_bonding.html
Protectors are only a simple science of protection. The
art is in the earthing. More about earthing was discussed
previously in two threads in the newsgroup misc.rural:
Storm and Lightning damage in the country 28 Jul 2002
Lightning Nightmares!! 10 Aug 2002
http://tinyurl.com/ghgv and
http://tinyurl.com/ghgm
Should you wish to learn more, Polyphaser (another
manufacturer of 'real world' protectors) provides application
notes such as this one about single point ground:
http://www.polyphaser.com/ppc_PEN1002.asp
and others:
http://www.polyphaser.com/ppc_technical.asp
http://www.polyphaser.com/ppc_pen_home.asp
Additional information in some MTL Surge Technology app notes
at:
http://www.mtlsurgetechnologies.com/...tans/index.htm
Bottom line is this: a surge protector is not protection. A
surge protector is only as effective as its earth ground.
Notice no technical references to companies that sell
ineffective protection such as APC, Panamax, and Tripplite -
and other plug-in manufacturers so often hyped by myth. What
do they avidly avoid discussing to sell their ineffective
products? Earth ground. No earth ground means no effective
protection.
Sunny wrote:
I personally installed the electric service at my cottage 20
years ago, in accordance with all Canadian electrical codes in
effect at the time. IIRC, earthing involved banging two 8'
rods into the ground several feet apart and connecting them to
the neutral bus-bar inside the fuse panel, and also running a
cable from the same bus-bar to the cold water plumbing. The
phone company installed the phone service, which enters the
building beside the electric meter, but I don't know if/how
they effected earthing. The only other incoming wire is from
the TV antenna, on the opposite side of the building, which
currently has no earthing.
I would be greatful if you could explain, in laymans terms,
what further steps I could take to protect my cottage
electrical equipment from lightning strikes - since
unplugging doesn't work.
I have no reason to doubt your assertion that protection is
always possible, but I am having some difficulty translating
your advice into practice.
Thanks,
Sunny