Estimating the kVA load requirement
Check the data plate, manual or specifications for each machine intended for connection to the UPS. You can also go to our on-line kVA power estimator table which will help you to calculate your load (applicable for small/medium businesses only. For large networks and data centres, please contact us for advice).
If it states the power consumption in VA or kVA (unlikely but possible) you can add this to the total kVA consumption tally.
If it states the consumption in Watts (or KW) and the power factor, you can find the VA or kVA equivalent by dividing Watts by the power factor. For example a 400W desktop workstation with a power factor of 0.8 would draw 400/0.8 = 500VA.
If the power factor is not stated, then assume a value of 0.8 for rough estimation purposes. Note that this approach is not accurate enough for any formal specification because in reality the power factor can be anything from below 0.7 to unity, and there is also a question of 'lagging' vs 'leading' power factors.
Desktop workstations and many other machines typically present a lagging power factor, while blade servers, which are increasingly prevalent in large scale computing environments, present a leading power factor. See 'Other UPS impact factors' for more information on this issue and its impact on the UPS.
If the power consumption is not stated in Watts or VA, then check for the current consumption in amps (A). Multiply Amps by Input Volts to obtain the power consumption in VA. For example if a machine has a stated current consumption of 1.5A at 230V then this equates to a power consumption of 230 x 1.5 = 345VA. If the machine has a 3-phase input then this equates to a power consumption of 400 x 1.5 x √3 = 1040VA.
All of these examples are worst case scenarios in the sense that the power actually drawn by any machine should always be less than the stated capacity on the data plate or in the manual.