Uninterruptible Power Supplies can be one of the hardest aspects of your IT department to budget for, because you can always buy a bigger UPS. It's easy to envision nightmare scenarios with extended power outages,leaving you wondering how big of a UPS do I need?
There's always going to be a certain amount of guesswork involved with buying a UPS, as is the case with any disaster-level planning. The key to making a smart investment is to focus on the aspects you need, and then discuss how much backup battery time you'd like to add to the order.
How Big of a UPS Do You Need
1 - Start with your current power needs.
UPS systems that can't supply enough power to all the equipment attached to it will be useless in an outage, so your number one concern is finding a UPS with sufficient power output. This is simple, if perhaps time-consuming. Just add up the wattage / voltage of everything that's going to be plugged into the system. This is good information to add to your network inventory, so you don't have to gather it a second time. Then you'll have a quick-reference lookup whenever you need to make electrical changes. Both APC and Tripp Lite have free online UPS calculator.
2 - Look to the future.
Don't stop with just your current usage. You'll want room to grow, since every device added to the UPS will decrease its battery life or - worse - overload the system. So consider your future upgrade plans, and do a bit of research on how much more power you're likely to need in the next couple years. Otherwise, you may need a new UPS the next time you add a server or other large piece of equipment. If that purchase is foreseeable, it's more cost-effective to get a slightly bigger UPS today, rather than purchasing an entirely new unit in a year. 
3 - Can your equipment survive a shutdown?
Most typical office computers, telephones, and small servers can handle being shut down and rebooted with few problems, all other things being equal. However, as your network equipment grows larger and more specialized, its sensitivity to power failure grows as well. Some pieces of equipment basically can't ever be shut down. In other operations - such as those maintaining servers for customer access - certain computers may be so mission-critical that a shutdown would cost substantial revenues.
So look at the equipment on your network and make a realistic assessment of whether a power outage would be an inconvenience, or a disaster. If there's nothing that will react too badly to an outage, you probably only need a small amount of battery backup time, perhaps 15-30 minutes.
4 - Do you need a rollover UPS?
It's increasingly common for some businesses to employ multiple UPS systems, so that if one fails the next catches it. While these systems take up more space, much of the time, it can be cheaper to buy two smaller UPSes than buying one with a huge battery. We've also seen situations where this is deployed to allow a controlled stage-by-stage shutdown sequence in the event of an extended power failure. The most mission-critical network elements have the most Tripp lite UPS units backing them up, even as the rest of the building is allowed to shut down as the batteries drain.
5 - How much extra time do you want?
Finally, there's the "insurance policy" part of the purchase. No matter how much time you want to buy, there are batteries for it. We recommend having a chat with your financial office, and creating an hourly breakdown of the costs you'll see from an outage, versus the frequency of outages in your area. More batteries buy you more time, but it's a waste if you never have significant outages. Remember to check out that online UPS calculator or ask us for help.
Lastly, consider a generator...but that is a different article all together. If you'd like more specific advice on implementations made by organizations similar to yours, just drop us a line and we'll talk details!
