Protecting your computers and other equipment from power fluctuations.

Uninterruptible Power Supply (UPS)

Uninterruptible Power Supply (UPS)

OK, let’s get one thing straight from the start:

ALL electronic and computer equipment is very sensitive to power fluctuations. By fluctuations I mean the general day to day variations in the voltage of your power supply as well as power surges, brown-outs and power cuts. And you will all be experiencing these more often than you probably realise. I can’t remember the exact figure but our power supply is guaranteed not to fluctuate outside of particular tolerances. Most equipment can survive these fluctuations but it is anyone’s guess what long-term damage this is doing to your equipment. However, no equipment can survive the the larger fluctuations (surges) caused by local lightening strikes! I have seen the consequences of this many times.

So, what does this mean to your equipment and to your work?

You must protect your equipment from power fluctuations, surges and brown-outs and you can do this in one of two ways: install a good quality surge protection board or an Uninterruptible Power Supply (UPS). The cost can easily be justified against the cost of repairing or buying new equipment plus the cost of downtime.

Surge Protection Board

Designed to protect equipment against a power surge, or an over voltage in the power supply.

All your equipment should be plugged into at least a good quality surge protection board. By good quality I mean one purchased from an electronics shop or your computer supplier, not one from a discount store! A surge protection board does just what it says: it protects your equipment from power surges by using a cut-out switch that will automatically isolate your equipment if there is a power surge. Yes, this means your equipment will immediately shut down when this happens and you will probably lose any work you haven’t saved but it will preserve your equipment.

Surge protectors come in a variety of types and number of output, or load sockets. Just to confuse you there are also “overload protection” boards but you don’t need one of these! Get a surge protection board with enough sockets for your needs or get more than one. It doesn’t matter if they have individual on/off switches or not. Some of the better boards also come with insurance which will payout for any damage to equipment connected to the board if they fail to do their job! And from what I have read, they do actually pay out on this insurance cover if the worse happens.

You should protect all of your electronic equipment: computers, laptops, monitors, external disks, printers, scanners, fax machines, ADSL modems, routers, tablets, phones, etc.

You will have noticed my comment in the previous paragraph, “your equipment will immediately shut down when this happens and you will probably lose any work you haven’t saved”. Surge protection boards will cut-in immediately they detect a power surge out of tolerance and you will not have enough time to save your work and complete a controlled shut-down of your computers and servers and this could mean lost or corrupted data as well as damaged PCs which won’t restart. This is where a UPS comes in.

Uninterruptible Power Supply (UPS)

Designed to provide backup power in event of a power outage with the added advantage of protecting against power fluctuations.

These were originally only found in corporate data centres and consisted of huge banks of batteries connected in serial and sometimes a backup diesel generator. Power was supplied to the computer equipment through a system which kept the batteries charged and at the same time supplied stable alternating power to the computer equipment at a steady voltage. When the mains power went off the batteries took over (with no interruption to the supply). The batteries supplied power through an alternator for a certain amount of time, usually something like 15 minutes, which was time enough for either a clean shut-down or for the diesel generator to come on-line and start to supply power.

UPS’ are now available for small offices and home users for their servers and desktop systems. Of course, they are much smaller and much cheaper! These smaller UPS’ sit between your computer and the wall socket and if the power fails or drops significantly even for a microsecond the UPS will take over and supply power to your equipment from its battery.

Most consumer type UPS systems are designed for one computer or server and maybe a monitor and one other piece of equipment. Depending on the amount of power drawn by the equipment they will supply typically, 5-15minutes of power from their batteries. They normally have 2 or 3 UPS sockets and some also have extra sockets with just surge protection, the idea being you can use these sockets for printers, etc. which do not need the UPS.

UPS’ are rated in VA or VoltAmperes,

Before buying a UPS you need to consider a number of things: what equipment needs to be on the UPS, how much power that equipment will draw and how long you want it to supply power. Remember that most of our power outages only last a few minutes so you may not even realise you are running on the UPS.

In most instances, your UPS will only have enough backup power to allow you to save your work and perform a controlled shut-down of your computers. If you need longer you will have to buy a larger and more expensive UPS. The cost is in the batteries. As the battery time is related to the amount of power the equipment draws you can use multiple UPS, one for each computer, etc to give you more time, but realistically you can’t expect more than about 15-20minutes of battery time.

So, the first step is to audit your equipment by adding together the equipment’s Wattage rating (computer, monitor, speakers, and anything else to be plugged into the UPS). Now you can work out what size, in VA you need in the UPS. Of course nothing to do with technology is ever simple so here is a rough rule-of-thumb calculation:

The wattage rating of a UPS is approximately 0.6 * its VA rating so, as you have seen, a 700VA UPS is good for a power load of around (0.6 * 700) = 420W . Conversely, the minimum VA rating you need is approximately 1.6 * load wattage.

Alternatively you can use a manufacturers online calculator such as this one here.

Without going into the technical aspects of a UPS, when purchasing I recommend buying a “line interactive” unit as opposed to an “offline/standby” unit. The former provides high levels of efficiency and reliability, as well as its relatively small size and low cost and at the same time provides a level of power conditioning (levelling out surges and dips in voltage) that the offline/standby does not do. There is a third type, online/double-conversion but these are quite expensive.


  • DO NOT daisy chain surge protection boards, at the least the surge protection will not work as it should and at the worst you could overload the power socket and blow a fuse!
  • When a surge-protection board has been hit by a large surge and tripped, replace it! It may not work properly afterwards.
  • You will require one UPS per computer.
  • Do not overload the UPS it won’t give you the required protection and the batteries will not last very long. 
  • Do not plug a power board into the UPS, you will overload it.
  • If you have expensive peripherals such as printers, then use a surge protection board or UPS for these.
  • If you want to a) protect your network equipment and b) keep the network and Internet connection running during a localised power outage, connect this equipment (ADSL modem, router, switch) to it’s own UPS!
  • As a UPS can cost a couple of hundred dollars or more we suggest that you plug it into a surge protection board to protect it! This will also give your computers another level of protection.


Most UPS will come with software for your computer. You connect the UPS to the computer, usually with a USB cable and install the software which provides a number of useful tools. First it can  monitor things like the load on the UPS and the battery condition (%charge, etc). Secondly, the software can be programmed to shut down the computer if you are not there, it can even save your work (such as a Word file) before shutting down!


Although most UPS batteries are replaceable they are likely to outlast the unit itself unless you have a really unstable power supply. I have never replaced a UPS battery yet.

And, like all electronic equipment a UPS must be disposed of responsibly and not just placed in the rubbish bin. Check with your local council or with a local battery supplier such as Battery World on recycling options.

Please contact us if you have any questions.