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From: peterb@pbear.UUCP
Newsgroups: net.micro
Subject: Re: MOV transient protectors
Message-ID: <58@pbear.UUCP>
Date: Sat, 23-Feb-85 04:19:08 EST
Article-I.D.: pbear.58
Posted: Sat Feb 23 04:19:08 1985
Date-Received: Wed, 27-Feb-85 05:15:09 EST
Lines: 48
Nf-ID: #R:brl-tgr:-835900:pbear:27000001:000:2044
Nf-From: pbear!peterb    Feb 22 13:30:00 1985


	Acutally 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.