lightning arrestors [RE-wrenches]

[Bill Brooks]

Jeremy,

There are all kinds of opinions about lightning arrestors. I believe that
they are effective fetishes that ward off the evil spirits of electrical
surges. Systems that use them tend to survive electrical storms and those
that don't, by Murphy's Law, get nailed. Not always the case, but seems to
be a tendency. There are apparently none UL-listed for higher voltage
systems, but some have been listed in low voltage systems. I believe Schott
Applied Power has listed a high voltage arrestors in their string
combiner-not positive.

They are Silicon-Oxide Varistors (SOVs). Silicon-Oxide is...sand...so this
is sand with some wires stuck in it. When a high voltage is presented
between the current-carrying conductors and ground, current begins to flow
from the ungrounded conductor to ground--through the sand. The sand heats up
and absorbes the energy by forming glass. Glass has a lower density than
sand so it expands and breaks the case of the SOV (that is why all SOVs have
either plastic or porcelin cases). They usually fit in a 1/2" knockout so
that they can be mounted on the bottom of NEMA 3R enclosures. They should be
visible so that it is obvious when they are used up.

Bill.

-----Original Message-----
From: jeremy page [mailto:jevanp05 at yahoo.com]
Sent: Thursday, March 06, 2003 10:17 AM
To: RE-wrenches at topica.com
Subject: SPAM: lightening aresstors [RE-wrenches]



I know on all pulse systems they use these lighting aresstors. but i'm
not sure what there true purpose is and in what other applications they
would be used in. if anybody can explian how these work i would
appreciate it, thanks
                  Jeremy Page
                  www.n-v-t.com

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