Re: http://h71000.www7.hp.com/?
- From: "w_tom" <w_tom1@xxxxxxx>
- Date: 17 Jul 2006 15:19:04 -0700
Two principles to first understand how switches are damaged. First,
all switches already contain effective protection. Second, protection
may be overwhelmed if a transient finds a path to earth via that
switch. Nothing - not a protector, not a fuse, not a magic box - will
stop block or absorb the destructive surge. And yet we routinely
suffer direct lightning strikes without damage - see the telco example
provided later.
Solution is also found in a principle pioneered by Ben Franklin in
1752. Don't even try to stop or absorb a surge. Shunt (divert) it.
That is what a shunt mode protector does. Lightning seeks earth
ground. If you don't earth a transient where it enters the building,
then transient will find destructive paths via electronics.
Destructive surges are electricity. Electricity means both an
incoming and outgoing path must exist. If a surge enters on a switch
and has no outgoing path, then no electricity flow; switch is not
harmed. However all switches have numerous incoming and outgoing
paths. Incoming on AC electric (the most common incoming path) and
outgoing via signal lines - especially those line connected to telco
wires.
Telco lines already have an effective 'whole house' type protector
connected short to earth where their wires meet yours. Therefore phone
lines are typically not an incoming path. But that telco 'provided for
free' 'whole house' protector makes a good outgoing path. Incoming on
AC electric; outgoing on phone line. Just one example of how
electronics are routinely damaged. Parts that often fail are on DAA
(telephone wire) side of that path.
Solution is not found in adjacent protectors. Solution is to earth
every incoming utility wire to a common (single point) earthing
electrode AND make that earthing connection as short as possible (ie
'less than 10 feet'). That means all utilities must enter at a common
location - to be earthed short to the same earthing electrode.
Distance is critical which is why wall receptacles are not sufficient
as earthing.
'Whole house' protectors for AC electric are sold in Home Depot,
Lowes, and electrical supply houses. These effective solutions are not
sold in Radio Shack, OfficeMax, Kmart, Sears, Staples, Circuit City or
other sources of ineffective protectors. Effective solutions have
responsible names such as Siemens, Square D, Cutler-Hammer, Leviton,
Intermatic and GE. Effective protector has a wire for the dedicated
earth ground.
Even some RJ-45 ethernet protectors have that all so necessary
earthing wire. But again, a protector is only as effective as that
connection to and quality of earth ground. Earthing - not the
protector - determines whether appliance internal protection is
overwhelmed. You had damage from a nearby strike (which is really more
often a direct strike)? Then look at your protection system.
Where is the path to earth? Through a non-destructive path (as Ben
Franklin demonstrated) or via electronics? Most critical component of
every protection 'system' is the component that everything else centers
upon - a single point earth electrode.
Above defines secondary protection. Primary protection 'system' also
must be inspected:
http://www.tvtower.com/fpl.html
Why does damage occur? Because a transient was not earthed where
wire enters a building. Therefore the transient found a destructive
electric circuit - incoming and outgoing path - through electronics.
Your telco connects its $multi-million computer to overhead wires
everywhere in town. Do they shutdown for a thunderstorm? Of course
not. Is that computer damaged by thunderstorms? It must not fail.
What do they do? Same thing. A good earth ground AND all incoming
wires first connect to that earth ground via a 'whole house' type
protector and before entering the building. A technique well proven
for maybe 100 years. A technique so well proven that surge damage is
considered human failure. It is that routine to eliminate. Switches
failing? Start by inspecting the earth grounds for each - the primary
and secondary protection 'systems'.
One poster in the 15xxx zip code may live where geology tends to make
transient damage from every ground strike most destructive. Damage is
often defined by geology. Some therefore must make the single point
building ground so large as to enclose the building inside either a
halo or Ufer ground. Again, protection is defined first and foremost
by the quality of earthing. Damage being a human failure. No earth
ground means no effective protection. No way around technology that
was standard even before WWII.
Thomas Wirt wrote:
Dave Froble wrote:
I have replaced many switches that went bad NEAR lightning strikes. I
have been chalking these up to EMP/induced current for a long time. I
figure that when you get a nearly vertical lightning strike near (within
a couple hundred feet) a large horizontal copper antenna (like a 250ft
CAT5 run), it should be pretty easy to get some combination of EMP and
induced current.
We have started taking a fool me twice shame on me attitude. When we
have a switch port (or usually a group) go out in a storm, we add CAT5
lightning arrestors at each end of the CAT5 cable. It is usually easy
to guess which line is the cause. Just look for the long copper run
that has a damaged device at BOTH ends.
I may not know what I am talking about, but since we started protecting
and eliminating our longest copper runs, we have had way fewer switch
problems.
.
- References:
- http://h71000.www7.hp.com/?
- From: Mark Daniel
- Re: http://h71000.www7.hp.com/?
- From: Bob Gezelter
- Re: http://h71000.www7.hp.com/?
- From: Dave Froble
- Re: http://h71000.www7.hp.com/?
- From: Thomas Wirt
- http://h71000.www7.hp.com/?
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