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Posted by w_tom on July 13, 2008, 9:19 am
> I already answered this. One protector is a lot cheaper than 4 scattered
> throughout the house.
> ...
> "Earthing" would be critical to a lightning surge. A power plant surge i=
s
> not returning to earth, its returning to the plant. The return path is t=
he
> critical key. Is that path through your device, or through the ground.
> And how do you get the surge to prefer the ground over the ordinary path.
> ...
> Earth does not sink energy that it does not create. Earth ground is only
> relevant for lightning surges. ...
> Surges must return to their originator. That may be earth, it may be the
> power company.
>
> If you are an EE then lets get down to the fundamentals of why you
> think "impedance" and not RELATIVE impedance is the key here!? I don't
> need citations that you think support your point. Just explain the
> fundamentals of your point.
Power plant surges don't create consumer surges for numerous
reasons. But lightning and other surges such as those created by
utility switching may be destructive and do seek earth. Also install
one 'whole house' protector for typically non-destructive surges. We
install and earth one 'whole house' protector to protect from all
types of surges. The word *all* does not apply to plug-in protectors.
Install only four plug-in protectors around the house. If a plug-in
protector works as claimed, then we need maybe 100 plug-in protectors
including one at the furnace, one at the dishwasher, and one for every
far more critical appliance such as bathroom GFCIs and smoke
detectors. That is the kind of protection obtained from one 'whole
house' protector. Meanwhile, plug-in protectors do not even claim to
protect from the typically destructive surge and can even provide that
surge with more destructive paths through appliances (Page 42 Figure
8).
Instead of 100 plug-in protectors selling at $25 or $150, the
informed consumer installs superior protection from all types of
surges using only one properly earthed 'whole house' protector.
Superior protection for only $1 per appliance. Yes, you agree. But
this post is for many - not just you. Four protectors scatter around
the house does not even approach being sufficient or effective. Four
protectors - and not one provides a manufacturer spec for protection
from typically destructive surges? What kind of protection is that?
Profitable. Ineffective.
I don't know what your 'relevant impedance' is. But wire impedance
is why effective protectors are located close to earth AND separated
from appliances. Wire impedance for earthing concerns industry
professionals. A 'top of the front page' article in Electrical
Engineering Times entitled "Protecting Electrical Devices from
Lightning Transients" discusses what is required for surge protection:
http://www.planetanalog.com/showArticle.jhtml?articleID=3D201807830
> Another aspect of impedance ... of a wire is predominately related to
> its length and weakly related to its diameter. ... The length of the
> cable increases the impedance dramatically.
The article is about surge protection. Therefore it describes what
is essential - a low impedance earth connection. It is about
effective protection. So it does not discuss plug-in protectors.
Any facility that requires effective protection earths surges at the
service entrance, worries about connection impedance. and addresse
grounding issues should damage not be averted. A plug-in protector
cannot protect from typically destructive surges. Its manufacturer
makes no such claims. Obvious: plug-in protectors are not used inside
telephone switching centers where damage must not occur and therefore
'whole house' protectors are used.
Protection inside appliances makes most surges irrelevant. A
typically destructive surge can overwhelm that existing protection.
So we install and better earth one 'whole house' protector to make a
typically destructive surge irrelevant AND to make other surges also
irrelevant.
Where does the US Air Force demand that protectors be located? Not
inside:
> Grounding Systems
> Introduction. This section covers requirements for grounding
> and lightning protection systems,including systems installed
> on or in areas such as explosives buildings, magazines,
> operating locations and shelters.
> ...
> 15. Surge Protection.
> 15.1. Entering or exiting metallic power, intrusion detection,
> communication antenna, and instrumentation lines must have
> surge protection sized for lightning surges to reduce transient
> voltages to a harmless level. Install the surge protection as
> soon as practical where the conductor enters the interior of
> the facility. Devices commonly used for this include metal
> oxide varistors, gas tube arresters, and transzorbs.
Why at the service entrance? Any surge that might be stopped or
absorbed inside a building will simply find many other (some
potentially destructive) paths inside that building. A surge earthed
before entering the building means protection inside *all* (not just
four) appliances is not overwhelmed. A surge earthed at the service
entrance (ie breaker box) means a low impedance connection into earth
AND a high impedance path to appliances. Essential to effective
surge protection is that low impedance earth connection. Then surge
energy gets dissipated in earth; not inside the building. Routine is
to have direct lightning strikes and no damage.
A 'whole house' protector also makes that other typically non-
destructive surge irrelevant for tens or 100 times more money.
Of course this is not 100% protection. From the IEEE Green Book
entitled 'Static and Lightning Protection Grounding' :
> Lightning cannot be prevented; it can only be intercepted or
> diverted to a path which will, if well designed and constructed,
> not result in damage. Even this means is not positive,
> providing only 99.5-99.9% protection. ...
> Still, a 99.5% protection level will reduce the incidence of direct
> strokes from one stroke per 30 years ... to one stroke per
> 6000 years ...
Where does a plug-in protector costing tens or 100 times more money
per appliance make any such claim? It doesn't. One glaring reason -
no low impedance connection to earth.
Surge created by a high voltage transmission line falling onto local
distribution is energy from the power plant (actually transformer that
is sourcing power) seeking a path back to that power plant via
earth. A surge so violent as to literally explode hundreds of
electric meters 10 meters off buildings did not cause any appliance
damage when one 'whole house' protector (and no plug-in protectors)
was properly earthed.
A surge that entered a building of powered off and networked
computers was simply earthed, destructively, by two plug-in protectors
through those adjacent computers and through the network. We traced
that surge by literally replacing ICs. What kind of protection from
two plug-in protectors? Completely ineffective as demonstrated on
Page 42 Figure 8 - 8000 volts earthed through the adjacent TV.
Why spend so much money on protectors that cannot and do not claim
to protect from the typically destructive surge? Why waste money on
plug-in protectors? Because it is the popular thing to do.
Facilities that must have protection don't waste money on plug-in
protectors. Instead 'whole house' protectors AND short (low
impedance) connections to a single point earth ground are installed.
Earthing is critical for protection from all typically destructive
surges. Same protection 'system' also protects from all other
surges. No plug-in protector can or does make that claim.
Effective protection protects from all types of surges =96 including
the type that is typically destructive. Where does any plug-in
manufacturer make that protection claim?
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