UPS Basics: How To Choose The Best UPS

Selecting a UPS can be a tricky decision. Online or offline? Modular or static? Follow our ‘UPS Basics’ guide and make sure you choose the best power protection for your circumstances.

Choosing the right uninterruptible power supply is crucial. Oversize during initial installation and you’ll likely be running an inefficient system that wastes unnecessary energy. But if you undersize, you run the risk of incurring additional expense to provide the required capacity.

Similarly, an industrial installation at a factory or power plant will have completely different needs to a data centre where rack space is at a premium.

So what key criteria should you weigh up when selecting a UPS? Our ‘UPS Basics’ film covers all the most important aspects, from whether a load is critical or not, the installation environment and space needed for ventilation and UPS maintenance, climatic conditions, and how to achieve the required redundancy.

Video Transcript

Hi I’m Steve. Selecting the right UPS for your customers’ application can often be a daunting task. Which UPS topology do they need? What power capacity? Does it suit their environment? And many more questions need answering to ensure the correct UPS is selected.

The first and often overlooked issue is separating out critical and non-critical loads. A critical load should be categorised as equipment that you cannot be without during a power outage. A call centre will, of course, need computers and telephones to be active, but printers and desk fans aren’t essential.

An industrial environment may have production lines that could lose tens of thousands of pounds if a power outage occurred and stopped operations. But they may not mind dropping telephone lines and non-essential lighting during that time.

Establishing critical and non-critical loads ensures that not only are you selecting the right topology of UPS but you’re not over-sizing the UPS unnecessarily.

Selecting the correct topology of UPS is not always something you have a choice in. Line-interactive models generally stop at 3 kVA. Therefore if your load is over this figure your only choice is an online UPS.

If your load is below the line-interactive / online threshold, the customer must advise what type of equipment is being used and its criticality.

A line-interactive UPS is ideal for less sensitive loads like motors, pumps, or lighting. A line-interactive UPS would also be suitable for any non-critical server or telephone switches. But be careful. If the power supply is sensitive enough it may detect small switchover and shut down unexpectedly.

Online UPS is the perfect choice for sensitive or critical loads of any size.

Now that size and topology has been established, our next consideration is the installation environment. The environment in which a UPS is located can play a large part of the model that you choose. IT loads may require a rack-mount UPS, whereas this is rarely the case for more industrial type loads.

If a rack-mounted UPS is required, take into consideration rack space available. IT managers would rather fill their rack space with servers rather than batteries. The depth of rack is also an important factor.

Remember you also need to account for the space taken by electrical connections at the rear of the UPS. Floor-standing UPSs are generally more easily located within a building, but still require a suitable environment. A UPS has sensitive electronic components and so are not suited to the damp, dusty basement or roof void.

And remember, when winter is coming batteries need to be kept at a constant temperature and so a location exposed to climatic changes is again not suitable.

Whilst a UPS doesn’t require a clinically-clean environment, an ideal location for UPS is in a clean temperature-regulated room with minimal activity in the immediate surrounding area.

Once you have located a suitable area for the UPS and batteries, take into consideration the spatial requirements for both ventilation and future maintenance of the system. For example, some UPS have rear-venting fans and will require full side access for maintenance or battery replacement.

In this case, there would be a 300mm gap required at the rear and the ability to pull the UPS forward if located side-by-side with other equipment. However, some other units have top venting fans and require only front access for maintenance.

Other environmental considerations include floor loading capacities, humidity, corrosive atmosphere, and people. The human element of the UPS installation is a big factor often forgotten by the customer. Is the UPS in a suitable environment for the noise level emitted? And a UPS should not be easily accessible to non-authorised personnel given its criticality to business continuity.

Now that we found a suitable location for our UPS, let’s think about resilience. For the most critical applications, large UPSs offer the ability to be paralleled. This is where two or more UPS are connected to provide redundancy to the load.

There are many ways of achieving redundancy. A standard N+1 redundant UPS solution is achieved by connecting two equally-sized UPSs together. The UPS then share the load and if a fault event occurs in one of the UPSs, the secondary UPS will take over the load completely.

Alternatively, a modular configuration comprising multiple modules within a single system cabinet ensures both future expansion and redundancy. More than two UPS can be paralleled if required to create a multi-MVA system or to achieve greater levels of redundancy.

Following the guidelines in this video will help ensure a worry-free UPS installation.

Watch the complete UPS Basics series: