On Fri, 08 Dec 2006 15:47:18 +0000, Phil Camera wrote:
Each of Phil's posts have been right on about grounding. I'll add
another important point that seems to be overlooked by many here on
the topic of surge protection.
MOV surge protection is a really bad idea on branch circuits. The
only GOOD application of an MOV is a very beefy one AT THE SERVICE
ENTRANCE. Why?
Let's say you have an MOV "protecting" a computer at one outlet,
interconnected to a printer at another outlet, and a cable modem at
another outlet. When the MOV fires, it conducts the surge (lightning
or otherwise) on the green wire, and the resulting IR drop in that
green wire raises the voltage on the chassis of equipment connected
to THAT OUTLET to a very high value. The two ends of the cable
connecting equipment powered from a different outlet will see the
very high voltage at one end and a very low voltage at the other
(or, if MOV "protected," a different very high voltage). That
potential difference can, and usually will, blow up equipment at
either end. This is the likely mechanism by which Pete's computers
were toasted.
Another reason MOV's are a really bad idea is that they fail or
"work" at reduced capability after having dissipated some finite
number of joules, but you often don't know this until it's too late.
In the pro audio world, we have lots of expensive interconnected
equipment at widely separated locations. Pro audio folks have
learned the value of SERIES MODE surge protection. The SurgeX line
of products use only series-mode surge protection, and have
established an excellent track record. They are the only protection
product I use on branch circuits. They are not cheap, and you won't
find them at Sams Club or Costco. But neither is my ham gear, nor my
computers, nor my home entertainment equipment. :)
Full disclosure -- as a consultant, I occasionally do work for good
manufacturers, and I have done work for SurgeX in the form of
technical writing and occasional telephone support/troubleshooting.
My recommendations are entirely independent of that -- indeed, I
specified SurgeX products in all of the big audio systems I design,
and bought and installed in my own home/office long before I did any
work for them.
73,
Jim Brown K9YC
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