Path: utzoo!attcan!uunet!husc6!mailrus!ames!umd5!uvaarpa!virginia!kesmai!dca
From: dca@kesmai.COM (David C. Albrecht)
Newsgroups: comp.sys.misc
Subject: Re: Protecting computer equipment
Message-ID: <177@kesmai.COM>
Date: 1 Jul 88 21:44:51 GMT
References: <1188@gmu90x.UUCP>
Organization: Kesmai Corporation, Charlottesville, VA
Lines: 84

In article <1188@gmu90x.UUCP>, dana@gmu90x.UUCP (J Dana Eckart) writes:
> 
> As my investment in computer equipment increases, I become more and
> more concerned about how to protect it.  Namely, what can I do to 
> reduce the risk of damage via power and phone lines, particularly
> from lightning.  
> 
There are a number of ways to protect power lines etc.. from surges/sags
etc.   The most popular elements for surge protection are MOVs which
protect from surges by shorting the spike to ground.  The point at which
the MOV starts shunting to ground depends on the device so there are MOVs
for low-voltage lines like RS232 connects and phone lines and high-voltage
lines like AC power.  Most of the common plug surge protectors for the
power line, RS232 line and/or telephone line are based on these devices.
The more wires in the line you are trying to protect the more points at
which the surge can appear.

An RS232 surge protector will often only protect a few of the 25 lines.
Haven't pried apart a telephone style surge protector to see what they
protect.  Power-line surge protectors are dealing with only three lines
so they are often more sophisticated and offer protection of both of
the power lines to ground and also a MOV between the two lines.
More sophisticated line power protection devices will add filter networks
to eliminate Radio Frequency noise from the line and additional elements
to provide more protection than just MOVs alone.

A surge protector will
usually be rated for how much energy it can absorb in Joules (higher the
better) and suppression of RF noise it will suppress in DBs.

Line conditioners add voltage regulation to circuitry for surge suppression
and noise suppression.  The utility company isn't too careful about keeping
voltage at 110 and it will often vary substantially from that point.  If
they have a hard time keeping up with demand they might just lean it out
by reducing voltage to the community.  The voltage regulator will adjust
voltages within a certain range to maintain a solid 110 volts.  I have
a Tripp-Lite 1800 watt line conditioner and it regulates from 96v-138v to
a solid 110v, it also incorporates all the surge and noise suppression of
their ISOBAR line of surge protectors.  At 1800 watts I can put a
substantial amount of equipment on it and it only cost $200.  The 1200watt
model runs about $150 and should still handle every bit of
computer equipment you own.

UPSen come in two flavors on-line and off-line.  Off-line are supplys that
normally are monitoring the line but not adjusting its content in any way.
The off-line supply therefore will typically not have any better surge
and noise suppression than a good surge suppressor since it is probably
using a similar network.  Typically, it doesn't provide the voltage
requlation of a line conditioner.  It doesn't protect against overvoltage
(until the level of the surge suppression network which is high) and low
voltage isn't recognised until the voltage drops low enough to kick in the
backup circuitry (which is typically fairly low).  This kind of supply
also has a finite switching time required to recognise power failure
and switch to battery generated power.  Typical switching times are
on the order of 2ms.  The reason people buy off-line UPSen is that they
are often considerably cheaper than the on-line variety and they consume
very little power when they aren't needed.  They on-line variety is
always generating the power to your equipment it is just where it is
getting the input from that changes either line or battery.  Therefore,
there isn't any switching time and the power output is always conditioned.

I also have a KNAPCO 550 watt UPS which is an off-line type containing
some surge supression, no noise suppression that I know of.  It switches
in 2ms.  The price was very good (about $370 qty 1, and I got the qty 10
price which was even better).  The cheapest on-line varieties I have seen
run around $700 similar or less watt output.

If you want genuine protection against power outages then go with an UPS
system.  If protection against spikes is what you desire buy a good
surge suppressor (< $100).  A line conditioner will add voltage regulation
to spike and noise suppression for not too much more money (< $200).
For surge/noise/voltage/power-out protection go for the on-line UPS
or off-line with a line conditioner in front of it.

This will give you some measure of protection against nasty power lines
and surges from lightning that isn't direct hits.  The best protection
is still a foot of air between the plug and the wall :-).  Very close
lightning strikes can induce voltages in lengths of wire and fry all
sorts of unexpected components.  Best you can hope for is some measure
of security, it is unlikely you will ever get absolute protection.

Sorry about the length, but you asked for it.

David Albrecht