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Power Protection - Some thoughts from an end-user.

I would like to start by saying I am NOT (repeat, NOT) an electrical
engineer or a power systems person.  I have a fair amount of experience
from a victim's perspective with dirty power, and some attempts
at cleaning it up.

My experience is that there are three levels of power protection:
	A. Placebo (cutsie little things that turn off their
	   neon lights when they can't handle the line jolts,
	   but still leave your equipment open to damage).
	B. Single point solutions (Isolated attempts to protect
	   an individual piece of equipment without regard to the
	   total power environement).
	C. Serious protection for the total power environment.

Type A protection (if you want to call it that) may still be a very
cost effective solution, when coupled with a full replacement value
insurance policy (making sure the insurance company accepts your
placebo as "reasonable effort"), and faithful backups.  Basically,
you accept that the machine is going to get fried, and you just want
to get another one when it does.

Type B involves placing interruptors (devices that monitor voltage
and/or current, and disconnect your equipment from the power line
if things get out of hand), power filters (essentially transformers
that deliver "clean power" over a wide range of voltages), and
battery backup systems.  Some caution has to be exercised in the
selection of equipment, as some items interact adversly with
each other, and with the power supplies in the protected equipment.

If wandering voltages (not surges, just drifts and mild lows) are
involved, a constant voltage transformer may meet the need.  If the
ability to "finish up and save a day's work" is important even if the
lights go out, then a battery backup is in order.  Short duration
units (20 minutes or less) usually meet this need.  Some of these
Battery backup units (also called Uniterruptable Power Supplies
or UPS (some are, some aren't)), also provide surge supression
of one kind or another.  Reaction time for the surge supression
equipment, the amount of energy they can dissapate, and the amount
of time for the batteries to "engage" are all important.

In most cases (not all, but most) a battery unit that engages in
1/4 of a cycle (1/240 of a second with 60 cycle power) is totally
adequate.  Also, consider whether the equipment you are protecting
requires a pure sine wave for input.  Some battery units output a
Square Wave or a Modified Square Wave (sometimes called a Modified
Sine Wave) instead of the Pure Sine Wave delivered by the electric
company.  Square wave units are cheaper (generally) than their pure
sine wave counterparts for a given size (wattage).

The size of the unit depends on how much stuff you plan to hang on
it.  My MAC-II with a monitor and internal hard disk runs nicely on
a 300 watt Battery Backup.  If I were to add another disk, I would
either have to plug it in the wall (bad trouble if the wall plug
I pick isn't connected to the same ground as the rest of the system)
or buy a bigger backup system.

Another factor to consider is "in rush";  this is, loosely, the
amount of instaneous current used by the equipment during startup
or major component activation (like some laser printers do just
before printing the first page in a batch).  Last month I saw two
backup units blown to bits when a laser printer cranked up while the
units were running on batteries.  The amp load of the laser printer
was within the specs for the units, but the instantaneous load was
not...

Be generous in sizing your unit for future growth (mine was way too
big for the dumb PC it originally guarded, but that was five years
ago, and now it is barely adequate for my current system).  Compare
oranges to oranges; some vendors throw Kva (Kilo (=1000) volt-amps)
or va (Volt-amps) around in their ads; others use watts.  Va is easy:
it is just voltage x amps (120 volts at 2 amps = 240va).  Watts are
a little more involved; for very loose rule-of-thumb approximations,
figure 0.8 watts per Va (so my 240 Va above would be 300 watts).

Type C protection begins by analyzing the entire operating environment,
which includes the building you are in, its electrical attributes,
and the people in it (static electricity is one thing a battery unit
offers NO protection from).  For those interested, the

	National Technical Information Service
	U. S. Department of Commerece
	Springfield, Va 22161

has a 100 page document called

	Federal Information Processing Standard (FIPS) 94
	Guideline on Electrical Power for ADP Installations

which discusses power conditioners, grounding (more is not better),
life safety, static electricity control,...  It makes very good
reading.  I don't have current pricing, but I recall it being under
$15.00.

Lastly, no matter what anyone tells you, no surge suppressor,
battery backup unit, constant voltage transformer,... is worth
anything if your location takes a lightening strike.  If you want
REAL lightening protection, forget type A and B solutions;  "C"
might get you there, if your luck is good that day (my opinion,
and, as stated in the intro, a power specialist I am not).

Hope some of this is useful out there in net land,
Ric

Disclaimer:  The above are my opinions, and do not represent the
University of Arizona in any way.  Consult a power system professional
before buying anything!!!!


Ric Anderson			Bitnet: Ric@Arizrvax
Computer Center			Internet: Ric@rvax.ccit.arizona.edu
University of Arizona		AT&T: (602) 621-6701
Tucson, Arizona 85715