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From: jwi@lzfme.att.com (Jim Winer @ AT&T, Middletown, NJ)
Newsgroups: misc.consumers,comp.misc,sci.electronics
Subject: Re: Surge protector advice needed
Summary: Surge Protector/Line stabilizer/UPS
Keywords: surge protectors
Message-ID: <1221@lzfme.att.com>
Date: 23 Mar 89 22:18:22 GMT
References: <1099@wpg.com>
Organization: AT&T, Lincroft NJ
Lines: 84

In article <1099@wpg.com>, linda@wpg.com (Linda Guidry) writes:
> 
> One of my non-net neighbors has had some *serious* surge problems...
> 
> Given the fact that there are a jillion different surge protectors
> on the market these days, she'd really appreciate some suggestions 
> from electrical engineers and/or knowledgeable consumers concerning 
> the names of the better brands.
> 
> Also, what features should my friend be looking for to protect 
> computers and laser printers?   

Depends on what *serious* means:

	If you have frequent power-outs, you need a UPS
	(Uninteruptable Power Supply).
	If you only have power-outs twice a year during
	thunder storms, you don't. (But don't use the machine during
	thunder storms.) They include back-up
	power, voltage stabilization, spike protection,
	and RFI/EMI interference protection. They come in both
	square wave output (cheap) and sine wave output (expensive).
	Which you need depends on what you are plugging in --
	I think (but am not sure) that a switching power supply
	as used in most computers will not care. Anything with
	an actual motor running off the power line will care.

	If you have frequent brown-outs, but not power-outs,
	you need a line stabilizer. TrippLite makes them in
	600VA, 1200VA and 1800VA ratings. They automatically
	adjust for low or high line voltages. They include
	voltage stabilization, spike protection, and RFI/EMI
	interference protection, but not back-up power. I use
	the 1800VA version with my printer plugged in to the
	first stage filter and my computer at the 3rd stage
	filter. (See below.)

	If you have frequent power drops when the fridge or
	the furnace starts or another appliance starts, you
	need a private circuit to your computer or possibly
	a higher amperage service from the power company.
	Spikes will always accompany electric motors starting
	so you must have at least spike protection.

	If you get strange results when the vacuum cleaner is
	running, or when electric or radio equipment is in use,
	you need RFI/EMI filtering. It is available in the
	better spike protectors.

If you think you can get away with a spike protector, be sure
it includes RFI/EMI filtering. In general:

	It should have both common mode and transverse mode spike
	protection. The cheap ones have only one mode because 
	it requires only 1/3 the parts. The good ones are protected
	from both wires to ground and between the wires -- 3
	times the parts. The cheap ones start at $7.95. The good
	ones start at about $35, but price is not a guarantee.

	RFI (radio frequency interference) and EMI (electromagnetic 
	interference) are filtered out by a whole bunch of little
	parts. Again there is common mode and transverse mode. In
	addition, there is multi-stage filtering where the outlets
	are isolated from each other -- you plug the printer into
	the first level filter and you plug the computer intothe
	third level filter.

Unfortunately, the advertisers tell you the clamping time in
nanoseconds and the power dissipation in joules. If that's all they
tell you, don't buy it. Look for common AND transverse mode
clamping and EMI/RFI filtering. A reliable brand is Tripp-Lite (no
affiliation) which was an editor's choice in PC Magazine. If you
want specs on these things, you will have to look in the
reviews. The manufacturers don't provide them.

Jim Winer ..!lzfme!jwi 

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