Date   : Sat, 23 Feb 1985002:19:00-MST
From   : godot!ima!pbear!peterb%harvard.uucp@seismo.ARPA
Subject: MOV transient protectors

Actually one MOV would not work at all. You would need three,

MOV from :
       Hot to Neutral
       Neutral to Ground
       Ground to Hot

This protects the circuit from transients on any or any two of the
three legs of the feed. The real trouble is that the entire load of a
house can tax the MOVs unless you get the more expensive rated MOVs,
and besides most of the devices in the house are insensitive to
transients.

Second, the MOVs on the feed box would protect sensitive equipment
from the outside transients, but would not filter out the transients
that originate within a house. Yes the MOVs would trip and suppress
the transient, but also the power suppies of TV's, computers, etc
would also see the transient since they are on the short side of the
transient, so these devices would not have adequate protection.

The best advice is to install the MOVs as close to sensitive equipment
as possible and if you put MOVs in a outlet box, only plug in
compatible equipment into that box so that you can reduce possibility
of transients defeating the MOVs.

In my parents house, every spring the thundershowers knock out the
rectifiers in the TV. after two years and progressing through voltage
ratings up to the highest (~4Kv), I installed MOVs across the line AND
across the transformer output AND across the rectifier AND across the
output side of the logic supply. (Not across the tube supply of
course!) The cost was only about 15$, but after having the rectifier
replaced twice, and an entire main board replaced because the
transient took out most if not ALL of the IC's, I think the overkill
will save the boards. And for the last four years, there has not been
a single problem due to transients in the TV. (But transients did blow
the radio that was plugged into the SAME outlet).

This is why it is recommended that MOVs be placed in EACH item that
you wish to protect.

                                       Peter Barada
                                       ima!pbear!peterb

20$ of MOVs are worth more than the agrevation of blowing delicate
electrical equipment.