On Thu, 29 Sep 2005 14:52:11 -0500, Dave NØRQ wrote:
>I've never had a problem with it -- no RFI from it, and it has never acted
>up, even with 1kw of RF quite close to it. Nor have I had any equipment
>damanged by lightning --
It's important to understand what these devices do. These "whole house"
units are simply BIG MOV's that attempt to conduct the surge to "short it
out." In doing so, it must GO somewhere -- that is, current flows in some
complete path. Remember that the neutral is bonded to ground at the service
entrance, so there is no need for a protector between neutral and ground. A
line to ground protector conducts the surge to ground, so when a surge hits,
it will raise the potential of the safety ground (and neutral bus) by an
amount equal to the IZ drop between the panel and whatever lightning thinks
"earth" is. When you say "line-to-line," I assume you mean across the 240
volt secondary of a 120-0-120 circuit.
>but then, all the electronics plug
>into "real" lightning protectors (usually TrippLite) before plugging
>into the wall
Your definition of "real" in this case is flawed. Nearly all AC line
"lightning protectors" are nothing more than MOV's connected as noted above.
When they take a hit, they shove the surge into the equipment ground wire at
the outlet where they are plugged in, raising the potential at that outlet
in the presence of a surge. If equipment plugged into a "protected outlet"
is connected by low voltage wiring to equipment plugged into another un-
protected outlet, or even a DIFFERENT protected outlet, there can be large
potential difference between outlets that can blow up equipment. Thus,
typical power-strip MOV protectors are NOT "real" protectors.
The "real thing" includes 1) a good whole house protector and/or 2) a
SERIES-mode protector like those that SurgeX makes. I use SurgeX boxes, and
plan to add a "whole house" unit at the service entrance.
And, as has been pointed out on several occasions, it is critical that other
lines (telco, antennas, etc.)that can bring lightning into the house be
bonde and/or protected AT THE SAME POINT as the power line. Tom Rauch has
pounded on this for quite a while, and he is right on. That's often a lot
more difficult in some installations, but it's the right way to do it.
Jim Brown K9YC
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