Selecting the Proper UPS for your Application

Choosing a UPS System

Before choosing a UPS for your needs, we recommend you read this page and note the definitions explained. This will help you understand which model(s) are appropriate for your specific application, and why certain UPS types cost more than others. These definitions can apply to all makes of UPS systems, whether they are supplied by us or not.


The UPS VA Rating you require will depend on the load current of the equipment you intend plugging into the UPS.
To calculate the VA Rating : multiply the Amps of the equipment (normally indicated on a nameplate on the rear of the equipment, in the technical manual, or ask the supplier) you will use with the mains voltage you require and divide by the Power Factor (PF) of the equipment.


For example:

Your computer equipment requires: 5 Amps (current)
Mains voltage used: 120VAC (AC voltage)
Power factor of computer equipment : 0.6 (typical for computer equipment, unless the devices are power factor corrected)

5A x 120V = 600W / 0.6 PF = 1,000 VA (1 KVA)

So far, we see that you will require a 1,00VA UPS – but to cater for your future expansions and to compensate for the high peak currents and crest factors inherent in these types of loads, you should always add 100% capacity minimum to the UPS you choose. Therefore a 2,000VA UPS (2 KVA) should be used in this case.

If you are running a motor load, you must take the locked rotor current of the motor (in amps) and multiply it by the mains voltage (120 in this case) to get the MINIMUM rating of the UPS in VA. You must pay strict attention to this safety margin consideration when considering which UPS to use for reliable performance to occur.
For example:
Motor Locked Rotor Current: 20 Amps (current)

[typography font=”Open Sans” size=”13″ size_format=”px” color=”#fc0808″]Mains voltage used: 120VAC (AC voltage)
20A x 120V = 2,400 VA MINIMUM RATING FOR UPS[/typography]


Be sure to size any UPS being used with a motor load for the motor’s locked rotor (starting) current, NOT the running current. Sizing a UPS for the running current only will result in an overloaded condition if the UPS ever has to start the motor.

When choosing a UPS system it is a good idea to also plan ahead to cater for expansion so that your investment in a UPS does not outgrow your future needs – always choose the next size up when in doubt.

If several computers or pieces of equipment are involved, add all the Amps together and do the calculation as shown.
Please contact us if you need any assistance. We will gladly calculate the system for you if you provide all the relevant details.


The backup time is proportional to the load that is connected to the UPS. The more the load, the less the backup time, although it is not a linear scale. You can have backup time as little as 5 minutes, which will enable you to shut down the equipment connected to the UPS before the power fails, or up to 24 hours of backup time so you can keep your equipment running until mains power returns. All backup times shown on this website are rated at full load (load power factor of 0.8 in most cases,) for reference.


The level of protection you need will determine which of the following topologies is most suited to your needs. The main UPS topologies are:


Your computer is running at standard mains via a small limited AC Filter under normal circumstances (some systems do not have filters at all). After a power failure this type of UPS system switches, via a small relay, over to a simple inverter to provide power to allow you to save your open files and shutdown your computer.

The backup time is normally short and will depend on the VA rating (see definition above) of the UPS and the amount of power your equipment draws from it. This type of UPS will give you very limited or no protection against power surges, spikes and sags. Typical backup time = 5-10 Minutes maximum.

This type of UPS System is aimed at the personal & small business market and is mainly used when you have repeated, short power failures but a reasonably good mains supply. This type of UPS system is not recommended for critical applications or areas where there is bad or high fluctuating mains supply.

Power Level: from 250VA to 1,200VA

Protection level: Low


This type of UPS system will provide total protection and backup on power failure for critical applications, and therefore it’s the type offered on all Nova Electric UPS Systems. Your load is always running on electronically produced power, and it is not directly connected to the utility supply. The double conversion, double isolation and the pure sinewave form output ensures the cleanest, most compatible AC output for any critical load.

Typical backup time = 10 Minutes. External battery packs are available to extend the backup time to several hours. Many of our UPS Systems have intelligent RS232 as optional or standard equipment, with available automatic shutdown software and serial cable.

This type of True Online UPS System is aimed at commercial, industrial, and military applications, especially those with mission critical loads in areas where there is a very dirty, noisy & unreliable mains supply. This type of UPS system has the highest protection level available.

Power Level: from 500VA to 400+ KVA

Protection level: High


A parallel system is comprised of multiple UPS systems or UPS modules. These are installed so that they operate in parallel to support a common critical load. There are two main reasons for selecting this type of system: The first would be to increase the UPS capacity, which enables the system to power a larger load than possible with a single module. The second reason is to increase the system reliability by introducing modular redundancy. Redundancy can also be increased by connecting the UPSs in a series-redundant configuration.


Our RUPS 2000 software is available for Nova’s UPS systems, to enable you to monitor your UPS remotely. In the event of a power failure, the software can shutdown the computers connected to the system so that you don’t lose any data.


UPS systems, especially larger systems, require periodic maintenance. We offer service agreements tailored to each customer’s needs, ranging from basic maintenance to full service contracts. Please enquire. These services help to extend the UPS and battery life span.