When buyers are trying to select the right Uninterruptible Power Supply (UPS) for their home power protection needs, it can sometimes be confusing to sort through all the power-related terms that describe the “feeds and speeds” of the UPS. For instance, when reviewing the statistics listed on a typical UPS spec sheet or when reading the small print along the sides of the UPS box packaging, what does it mean to buy a UPS that is rated at 3 kVA vs. one that is rated at 1.5 kVA? Or what if the tolerance is 300 joules as opposed to 100? Is a 600-Watt UPS too big or too small for your needs? After all, most people who buy UPSs for their home or home office know that UPSs can act as both power surge protectors and power conditioners. The UPS prevents catastrophic surges from damaging electrical equipment, can level off sags and swells, and provides battery backup power when the power gets cut.
Understanding Power Terminology
But how can a UPS buyer be sure that he or she is buying the right UPS that best meets the power protection need without spending too much money? Many buyers are confused about the distinction between the watt (W) and volt-amp (VA) ratings as they pertain to UPS load sizing. They both have a use and purpose. The watt rating identifies the amount of utility power needed to run that particular piece of equipment. The volt/amp (VA) rating is used for the proper sizing of wiring and circuit breakers. The VA and watt ratings for some types of electrical loads, like incandescent light bulbs, are identical. However, for computer equipment the watt and VA ratings can differ significantly, with the VA rating always being equal to or larger than the watt rating. The ratio of the watt to VA rating is called the “Power Factor” and is expressed either as a number (i.e., 0.6) or a percentage (i.e. 60%). For example, a popular model of a home UPS, the APC Back-UPS Pro 1000, is a 1 kVA device that consumes 600 watts of power. (The term “kVA” simply means 1000 VA, the “k” being used in the nomenclature to denote 1,000).
Not all UPSs are designed the same way
UPS have both maximum watt ratings and maximum VA ratings. Neither the watt nor the VA rating of a UPS may be exceeded. It is a de-facto standard in the industry that the watt rating is approximately 60% of the VA rating for small UPS systems, this being the typical power factor of common personal computer loads.
“Joules” is also a power-related rating that often confuses UPS buyers. Most UPSs also act as surge suppressors. The number measured in “joules” is the amount of energy the suppressor can dissipate safely. On some surge protectors and UPSs, you may see “eP joule” ratings versus just a joule rating. Many APC home UPS products, for example, use the eP Joule rating because the device does not simply ‘absorb’ the surge like some of the less robust surge products might. The APC products are designed to redirect the surge back to ground instead of absorbing it. They also incorporate a “let through” voltage, which is the maximum transient voltage the attached equipment will be subjected to above the normal voltage. Any excessive voltage is redirected to ground.
Fortunately, buyers of home UPSs don’t need to understand the ins and outs of electrical engineering in order to make the right UPS purchasing decision. For Certainty in a Connected World and for information on how to make UPS selection easy and stress-free, access the new APC by Schneider Electric UPS Buying Guide today.