On 1/31/2013 4:26 PM, Don Wilhelm wrote:
We had a close lightning event last summer and there were no
incidences of damage on the AC side, although all the GFCI breakers
tripped.
The wired Ethernet devices were not so fortunate, I lost a router, 2 8
port switches, an access point, a NAS storage device, and 4 computers
after that event, that did not mention the Ethernet connected network
printer that lost its Ethernet capability, but still worked with a USB
connection - all apparently due to the surge coming in over the
Ethernet cables. Fortunately, no data was lost, the devices did not
work due to damaged network ports.
So the AC protection did work, but the unprotected Ethernet devices
did not survive.
The so-called surge protectors on your computers is what CAUSED your
Ethernet devices to fry. Shunt mode (MOV) protectors on branch circuits
are a REALLY bad idea.
MOVs at the service entrance are a very GOOD thing -- IF the house is
properly grounded.
The "high leg delta" is simply three Delta-connected transfomers on the
pole, one of which is center-tapped. There's 240V between legs, and if
you have 3-phase service from high-leg Delta, you get all three phases.
Customers who buy single-phase service (99.9% of homes) get both sides
of the center-tapped transformer and the neutral.
The (really) bad part of this is that ALL 3-phase systems have lots of
harmonic current, AND the single-phase get a super heavy dose of that
harmonic current on their neutral, which is the only path to ground for
it. THAT'S where "ground buzz" comes from.
A "whole house" surge protector has two BIG MOVs, one connected from the
two sides of the 120-0-120 to neutral, which is bonded to ground in the
entrance panel. For a 3-phase system, you simply need a protector with
one more MOV.
BTW -- the system I've described is called "high leg Delta" (also "wild
leg" or "red leg") because the terminal of the 3-phase system opposite
the transformer is 277V to neutral.
There's a discussion of all of this in the Power and Grounding tutorial
on my website. http://audiosystemsgroup.com/publish.htm Although it's
written for audio and video professionals, everything in it applies
equally to installations of all sorts, including radio.
73, Jim K9YC
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