Question about what UPS rating we require

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Can anyone with knowledge/experience give some advice regarding the
purchase of an UPS for our home computers?

Our main concern is to set up an UPS as protection against surges caused
by lightning. We don't really care how long the UPS can maintain the
computers running in the event of a power outage.

The main question is what size UPS do we require? We have two Pentium 4
PC's (2.4GHz + 3GHz) loaded with the usual peripherals (DVD/CD drives, 2
hardisks each) and two CRT monitors (19" and 17"). We also have a laser
printer and small hardware firewall.

We would like to keep the cost of a UPS down as much as possible. Can
anyone help with an idea as to the rating that we could get by with for
lightning surge protection? And a good tip on UPS model?

If the expense is too high to cover all equipment, we could also consider
protecting just the PC's and leaving the monitors and printer off the UPS.

Thanks for any help!

Steve, Denmark

Re: Question about what UPS rating we require

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First thing you have to know is that there are 2 types of UPS which offers
different levels of protection: on-line and off-line. With the on-line type,
the power out is connected to the power-in and in case of interruption, the
out is switched to an always loading battery. With the more expensive
off-line UPS, the out is only connected to the battery, and there is never a
direct connection between out and in, which offers a very much better
protection against voltage variations and lightning and does not involve any
switching time delay.
On top, both of those types can be interfaced (serial or USB) to the PC or
not. This allows the UPS to dialog with the PC, so you can monitor the
battery status, power consumption, aso. More important, you can program some
tasks in case of power failure, like closing all programs and do a clean
shut down.
What model of UPS you select is dependent on the type of activity you have
and how long you want your PC keep running after a power failure. Here
again, programming a PC shutdown could reduce the need of a heavy and
expensive battery. If you do video rendering the situation is different
because it can take a lot of time before the program could be closed.
Connectig a (laser)  printer to the UPS makes no sense. Same for CRT's as
those items take to much power. However, you could keep a TFT monitor on the
UPS without problems.
Maybe you could consider to buy 2 light UPS (400-500W), thus one for each
PC, instead of one single heavy unit for both, as this offers a more
flexible and less expensive solution.

Re: Question about what UPS rating we require

On Tue, 27 Jun 2006 09:12:15 +0000, ElJerid wrote:

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Thank you for the responses, both from Paul and from ElJerid.

The information provided by both replies makes this sound like it may
become an expensive affair, more than I wish to pay for. Perhaps the
simplest solution is to protect the PC's only and buy a smaller UPS for

However, I may have described what I need somewhat incorrectly, and
perhaps it isn't even an UPS device that I require. For us, it doesn't
matter whether the PC's shut down abruptly in the event of a power
outage. Our applications are not so critical that we need to worry about
this. Of course the operating system doesn't like this, but we have had no
major problems yet.

Our main and perhaps only concern is to protect the PC's from getting
fried in the event of a power surge. With this in mind, is there a less
expensive solution than an UPS that can keep the PC's going for xxx
minutes after a power outage? Is there hardware out there that would
mainly protect against power surges? The point here is we don't need a big
battery, we just need the surge protection.

Thanks again for any help or tips! And thanks again for the informative
reply from the two posters!

Steve, Denmark

Re: Question about what UPS rating we require

coolsti wrote:
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If you don't want to keep the equipment running long enough to do a
graceful shutdown then you don't really need a UPS -- you need a surge
protector. A really good surge protector capable or protecting all of
the equipment described costs less than even a mid-priced UPS which
would support only a portion of the loads. A UPS capable of running all
of the equipment you describe for even a few minutes, allowing that a
single laser printer can consume 1000W when its fuser is heating, would
be a very expensive proposition.

John McGaw
[Knoxville, TN, USA]

Re: Question about what UPS rating we require

   Buying a UPS doesn't have to be expensive.  There are places that
specialize in refurbished UPS equipment which will give you the same
protection considerably cheaper than purchasing a new UPS, just make
sure to buy from a larger company that specializes in UPS units.  A
good company that I've used before is Uninterruptible Solutions ( )  They have good prices and
are really helpful, you can give them a call and they can find
something that will fit your needs.

I think you are looking primarly for the surge protection capacity, but
using a UPS with a surge protector will provide very good power for
your application.  If your main goal is to protect your desktops, I
would recommend getting a good surge protector and a small UPS in the
400 watt range (700VA) and plug the UPS into the surge protector and
plug just the computers into the UPS unit.  This will filter out other
power problems such as under voltage, over voltage and brownouts as
well as allow you to safely shutdown your computer in the event of a
full power outage, which can be really useful if you are in the middle
of working on something!  Make sure to plug everything connected to the
computer into the surge protector, otherwise, surges can simply come in
through the monitor or the printer, etc.  Also pay attention to phone
lines, cable modem lines as they can also carry surges if they are
connected to devices which are connected to your computer.  Many people
make surge protectors that offer phone, ethernet or cable surge


coolsti wrote:
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Re: Question about what UPS rating we require

On 5 Jul 2006 08:38:38 -0700, wrote:

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I bought a 750 VA TrippLite unit called the Internet750U. I have a
computer, 19" monitor, officejet, cable modem and router plugged in.
It lasts at least 15 minutes, maybe even 30.

It has prevented utility line glitches from recycling everything on at
least a dozen occasions in less than a year. For that alone it is
worth it. It hooks to a USB port and can shut down the computer on a
preprogrammed schedule.

$69.99 at


Stop Repeat Offenders!
Don't Re-elect Them!

Re: Question about what UPS rating we require

  That post somehow assumes a power strip protector will somehow stop
or absorb a surge.  How?  How does that silly little component stop
what three miles of sky could not?

  They are called shunt mode protectors.  Look inside. Of for that
matter look at these pictures where the active component is removed:

  Protector components are removed and power still flows to lights and
receptacles.  Why?  Because shunt mode protector don't (electrically)
sit between electronics and the surge.

  They are shunt mode devices.  The surge that is seeking earth ground
is simply shunted (shared, connected, diverted) to all other wires.
But that surge is still seeking earth ground.  Where will it go?  One
destructive path is to earth via the electronics.

  Effective shunt mode protectors have a short ('less than 10 foot')
connection to earth.  They are called 'whole house' protectors.  A
shunt mode protection (that is effective) makes a connection from that
surge to what the surge wants - earth ground.  Any surge that is
shunted to earth where wires enter the building will not find earth via
household electronics.  One protector for the entire house with a short
path to earth.

  For computer data protection, use a UPS.  For surge protection, the
solution is located elsewhere - where all utility wires enter the
building - 'less than 3 meters' to earth ground.  Responsible North
American manufacturers make useful and effective protectors including
GE, Intermatic, Cutler-Hammer, Leviton, Siemens, and Square D. Fuse is
a European brand name.  Those who visit Home Depot, Lowes, and
electrical supply houses know these as responsible brand names.
Effective 'whole house' protectors are also sold in those locations -
not in your grocery store, Sears, Radio Shack, or Staples.

  They are shunt mode devices.  Effective protectors do not stop what 3
miles of sky could not.  They shunt.  They shunt effectively if that
all so critical 'less than 3 meter' connection to earth is provided.
Surge protection and UPSes functions are different.  For electricity
when the power goes out (to protect data), then you need a UPS.  For
protection from destructive surges (that seek earth ground), then you
need a 'whole house' protector on AC mains with earthing that meets and
exceed post 1990 National Electrical Code earthing requirements.
Protection is about earthing.  Effective protectors don't even have
components to stop or block surges as those zerosurge pictures
demonstrate.  And yet some would have you believe those silly little
components will stop what 3 miles of sky could not.

  Appliances already have internal protection.  Protection that assumes
you have earthed destructive surges long before those surges got
anywhere near to appliances.  The most critical component in every
surge protection 'system' is earthing.  Plug-in protectors avoid all
discussion about earthing for obvious reasons.  No earth ground means
no effective protection.  Best to let others believe a shunt mode
protector will somehow stops or absorbs surges. wrote:
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Re: Question about what UPS rating we require

w_tom wrote:

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The IEEE and the NIST both say plug-in surge protectors are effective.

The best paper I have seen on surge protection is at
- this a paper w_tom originally provided a link to
- the title is "How to protect your house and its contents from
lightning: IEEE guide for surge protection of equipment connected to AC
power and communication circuits"
- it was published by the IEEE in 2005
- the IEEE is the dominant organization of electrical and electronic
engineers in the US
- the 5 authors have broad experience with surge suppression

A second reference is
- this is the "NIST recommended practice guide: Surges Happen!: how to
protect the appliances in your home"
- it is published by the National Institute of Standards and Technology,
the US government agency formerly called the National Bureau of Standards
- it was published in 2001
- it was written by your favorite - Francois Martzloff - the NIST guru
on surges and lightning

Both guides were intended for wide distribution to the general public to
explain surges and how to protect against them. The IEEE guide was
targeted at people who have some (not much) technical background. Read
one (or both) to understand surges and protection.

Both say plug-in surge suppressors are effective.

Note that if a device, like a computer, has connections other than
power, like a phone line, they have to be connected through the surge
suppressor also. This type of suppressor is called a surge reference
equalizer (SRE) by the IEEE (also described by the NIST). The idea is
that all wires connected to the device (power, phone, CATV, LAN, ...)
are clamped to the common ground at the SRE. The voltage on all wires
passing through the SRE to the protected device are held to a voltage
safe to the device.

The primary action of a plug-in surge suppressor is clamping, not
shunting. w_tom does not recognize clamping as valid, and as a result
apparently can't read and understand these guides.


Re: Question about what UPS rating we require

w_tom wrote:

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You are confusing a direct lightning strike with induced voltage.  Lightning
can induce enough voltage into a power line without actually hitting the
line to damage your computer.  The same is true of the telephone line.

If you get induced voltage, whether or not your surge protector can handle
it depends on the induced voltage, and the capability of your surge
protector.  Most surge protectors will protect your equipment against most
lightning induced surges.

Jerry Pournell, writing in Byte magazine, many years ago had all of his
surge protectors fried and some of his equipment, when a drunk driver hit a
telephone pole and knocked an 11,000 volt line onto a 220v line that served
his neighborhood.

If you get a direct lightning strike, you may still be okay because it will
vaporize the power line or telephone line, and may do it before it delivers
the full power of the lightning strike.  If you do get a direct lightning
strike delivered to your computer by the power line or telephone line, it
will do more than just overpower your surge protector, it will explode your
computer, and anything else in your house that is connected to the power
line or the telephone line.  Fortunately this is pretty rare, induced
voltage is much more common.


Re: Question about what UPS rating we require

    There are actually 3 types and you have the on-line and off-line
more or less switched. I have an old Liebert 1500 VA on-line and love it.
sucker weighs about 80 lbs. See..
for the correct definitions.

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never a

Re: Question about what UPS rating we require

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    The owner of the company I work for bought 10 of these Liebert
UGX1500RTSE-60 w/ethernet at a bankruptcy auction. I don't know how
much he paid for the lot of 10, but they sold new for around $1,000 a
My job, a pleasant one, was to open them up, blow all the dust out and
clean and test them. When I was done, he told me I could have one and
I picked one that had appeared to be unused. They have loud fans and I
keep mine sequestered away in a closet. With good batteries, it will run
my system, including a 19" LCD, for over an hour during a power failure.
A common problem with cheap off-line ones is they often don't switch fast
enough and people find their computer "frozen". Not to mention the lack
of isolation and filtering. None of this is a real substitute for good
protection into the UPS though.

Re: Question about what UPS rating we require

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There is a selection tool here. The laser printer would generally
not be connected, as it would likely double the size of UPS you
would need to buy.

UPS are rated in watts and volt-amperes. One rating is for
purely resistive loads, and the other one takes the power
factor into account. A typical UPS rating might be 1440VA/865W.
Both ratings occur simultaneously, so 865W worth of light
bulbs can be used, or 1440VA at some power factor may be used.
You have to make sure your combination of loads, does not
exceed either rating.

The first couple of pages of this document, shows how you total
up both watts and VA, and compare to the rating of the equipment.
What they don't tell you, is a light bulb has the same watts as
VA, since a light bulb is purely resistive. A North American
ATX power supply, does not have power factor correction, so the
watts and VA have a ratio of 0.7 or 0.8. In Europe, active PFC
may be mandated for use with computers, so the ATX power supply
inside a European computer can have a power factor close to 1,
in which case there is no difference between the number used
for watts and for VA.

This page shows a picture of an ATX power supply with power
factor 0.7. This picture is not purely a power factor issue,
as the current waveform is also distorted (implying harmonics).

The bottom picture of the ATX power supply on this page, shows
an active PFC corrected (European) power supply. The power
factor is very close to 1.0, and this kind of supply means that
the UPS VA rating will not be exceeded. A UPS powering one of
more of these, is more likely to "run out of watts".

This document explains watts and VA a bit more:

For the computer itself, you still have to figure out what power
it is consuming, and the APC selection tool does not take modern
gaming systems into account. A computer with two high end Crossfire
video cards (2x120W) plus an FX60 (120W) is not accounted for by
the tool. The APC tool mainly deals with business desktops, where
the video card is a $50 joke. APC concentrates on the processor
or processor(s) used. If you had a high end gaming system,
then working out the demands with a hand calculation would be
a better thing to do.

To work out the power, you would take the DC loading on the output
of the supply. Say it is 200W. The ATX supply has an efficiency
rating. Say it is 68% when the 200W load is connected. Now we
are at 294W. This would be 294W at the input, and if the supply
is not power factor corrected 294W/0.6 = 490VA. If there is
active PFC correction, 294W/0.98 = 300VA. And you have to decide
just what power factor (0.6, 0.7, 0.8) is appropriate for the
non-corrected case.

So the power factor for each piece of equipment is a big unknown.
And the label on the back of the equipment, generally lists such
a big current, as to be useless for estimating the size of UPS
needed. You either have to rely on the selection tool, or try
your hand at doing the calculation yourself.

In the case of the 1440VA/865W example above, the power factor
of all the loads would have to be less than 0.6, for you to
"run out of VA". But other UPS may have a different ratio between
their VA rating and their Watts.

That is my understanding at least. I don't do this for a living :-)


Re: Question about what UPS rating we require

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If you want surge protection, get a surge protector (you could put
it in front of a UPS if you want a UPS also).  I would recommend
ZeroSurge: or one of the better

-- Bob Day

Re: Question about what UPS rating we require


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Then you need a surge protector, not an ups.  A proper "line
conditioner" would also be prudent if you have regular
surges, as surge protectors called that alone, can be
somewhat marginal protection, they attempt to divert surge
but it is in parallel with the system/other-stuff still in
most cases.

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A good 600VA or typical 750VA per system w/monitor.
What is the small hardware firewall? If just one of those
(roughly) 60 cul. inch boxes with a wall-wart to power it,
you could just plug that into the UPS with the lesser (17")
monitor.  The laser printer should not be put on an UPS at
all, they draw quite a lot (too much) current for any
typical consumer UPS to make it reasonable.

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There is no UPS rating (per capacity in current) that deals
with the surge protection.  An "online" UPS will be
inherantly filtering the power but it does nothing to
resolve the effectiveness of the surge protection vs. the
UPS rating.  The most cost effective is to not pay for the
"UPS" functionality at all, only the line conditioner
(stand-alone device), or put the money into a savings
account to pay your insurance deductible after the damage
occurs... and a little set aside to buy data backup
equipment that is NOT powered, unplugged when not actively
making the backup (unplugged means truely unplugged, not
shut off by a switch especially if connected to the LAN as
you still had a ground path if only turned "off" by a
typical switch).

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A surge protector, (not an UPS) of reasonable quality can
easily handle all the gear you describe, including the laser
printer, there would be no savings trying to protect only
some of it.  A line conditioner on the other hand would
typically cost more in proportion to it's current rating and
thus you'd leave at least the laser printer powered without
it.  Considering your CRTs are aging already and not so
valuable I'd also consider leaving them off the surge
protector, though leaving them on an UPS if you had any
ideas about trying to use the systems for the moments an UPS
could power it after a power failure.  You haven't mentioned
power failures as the problem though, so an UPS is not what
you are describing a need for.

Re: Question about what UPS rating we require

Thanks to all the responses!

I had been confused, I was lead to believe that a UPS is what I needed
also for surge protection, but due to economics, that is not the case
here. I will take the tips in this thread and look after a good surge

Thanks again!

/Steve, Denmark

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