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From: wmb%Ucb-Vax@sun.UUCP
Newsgroups: net.ham-radio
Subject: MOV transient protectors
Message-ID: <8713@brl-tgr.ARPA>
Date: Wed, 27-Feb-85 10:15:02 EST
Article-I.D.: brl-tgr.8713
Posted: Wed Feb 27 10:15:02 1985
Date-Received: Sun, 10-Mar-85 06:52:20 EST
Sender: news@brl-tgr.ARPA
Lines: 31

> What is the proper configuration for hooking up an MOV to a power
> line?  (i.e.  in series or in parallel?).

Parallel.

> If it hooks up in parallel to the power line, why wouldn't one MOV
> work for your entire house?  It seems that it would, because all the
> lines in the house are connected to together in parallel.

That would work if you expect all the transients to be developed on the
wiring outside of your house.  This may be a reasonable expectation in
some instances.  However, if you are interested in protecting againt
lightning strikes nearby, there could be significant spikes induced
in the wiring inside the house.

The other problem with using one MOV for the whole house is protecting
the MOV's.  MOV's are sort of like big zener diodes, in that
above a certain voltage, they start conducting heavily, but below that
voltage they don't conduct very much.  Notice I said "sort of", because
they don't work on the same principle as zener diodes, nor are their
breakdown characteristics as sharp or as well-defined as for zeners.
Anyway, the problem is this:  when the voltage across the MOV reaches
the breakdown voltage and it starts conducting, something has to limit
the current flow or the MOV will be itself destroyed.  Typically, the
current is limited by the resistance and inductance in the wiring.
Since the wiring coming into a house is typically much heavier than the
internal wiring, it is not as effective at limiting the current into
the MOV as the smaller gauge internal wiring.  This means you need a
bigger MOV.

Mitch Bradley