Business UPS Buyers Guide

Business UPS


A UPS intended for use in a business environment will usually need to protect many different devices. This could be PCs, phones and printers on a small office floor and / or for servers and networking equipment contained within rack cabinets. The more complex the array of devices a UPS is required to support, the greater the time likely to be required to close applications, save data and gracefully shut down numerous mission-critical pieces of equipment.

In a business environment as illustrated all the devices - PCs, servers, switches - will be connected to the power distribution unit (PDU) located within the rack cabinet using IEC C13/C14 (kettle lead) cables or in some high-end installations IEC C19/20 connectors rather than household 3-pin plugs. The UPS will typically have network management capability enabling it to send commands to the any network connected devices in the event of a power outage. Depending on the size of the business setting and numbers of devices will determine whether a tower (free-standing) or rack mounted UPS will be the best choice.

Tower UPS

Rackmount UPS

Types of UPS

There are three main types of UPS with differing capability and ability to control connected devices. These are Offline or Standby UPS, Online UPS and Line Interactive UPS.

The Offline / Standby UPS is the most basic out of the three. It provides light surge protection and battery back-up. During normal operations, it gets its power from its main power source (generally an AC outlet). Once it senses that the main power source goes beyond acceptable limits or fails, it switches to the offline / standby battery where it will then go to the DC/AC inverter – as such, there will be a small transfer time between the main power source and battery.

An Online UPS differs from an Offline / Standby UPS as the DC/AC inverter is always connected on. This means there will be no transfer time between the main power source and battery, providing greater protection against spikes, sags, electrical noise, and complete power failure.

Finally, a Line Interactive UPS has a similar design to an Offline / Standby, but with properties of an Online as well. A Line Interactive UPS can handle small under-voltages and over-voltages (about 20% from its standard voltage) by using a multi-tap variable voltage autotransformer or buck-boost converter. Even during these small under/over-voltages, the battery is not being used and is still being charged until there is a big under or over-voltage. Like an Online UPS there is no delay in switching power sources in the event of a failure.

UPS Type Benefits Limitations Value Proposition
Offline /Standby Low cost, high efficiency (typically 95 – 98%), compact Uses battery during brownouts, limited or no protection against power irregularities, impractical over 2kVA Best value for smaller businesses
Online Near ideal electrical output, highest protection against all power irregularities, ease of paralleling Lower efficiency (typically 80 – 90%), relatively more expensive under 5kVA Default choice for providing back-up power and protection to mission critical equipment and servers at datacentres
Line Interactive High reliability, high efficiency (typically 90-96%), reasonable voltage conditioning Impractical over 5kVA, does not protect against all forms of power irregularities Most popular UPS – ideal for for small office, web and departmental servers and/or harsh power environments

UPS Sizing

There are several factors that influence sizing a UPS system, including the combined load of all the equipment the UPS will protect, scope for further system expansion, battery runtime and redundancy. Correctly sizing an uninterruptible power supply is crucial as it will not power all the connected devices in the event of a failure if the battery capacity is too small.

The first step is to calculate the total power range for the combined critical load that needs protecting. The power consumption of electrical equipment is stated in either Watts (W) or Volt-Amps (VA), and equipment labels and supporting technical manuals will provide information on volts, amps and overall power consumption. Because UPS systems are rated by VA or kVA ratings, this may require a conversion from W to VA.

1. List all equipment to be protected by the UPS - remember to include monitors, external hard drives, routers, etc.
2. List the amps and volts for each device. Then multiply amps by volts to determine Volt-Amps (VA). Some devices may list their power requirements in watts. To convert watts to VA, divide the watts by the power factor. For most devices, the power factor is 0.9.
3. Add the VA values from all the devices together.
4. Then multiply this by a figure such as 1.2 or 1.25, which factors in future growth and system expansion. That figure is the maximum size in VA or kVA that your UPS should be. Note that a UPS should never be sized to run at 100% load capacity, as this isn’t recommended for safe, stable and reliable performance.

Let’s look at an example that may represent a typical office:

4x Servers - 1200W each
20x PCs - 400W each
20x Monitors - 25W each
2x Switches - 75W each

4x 1200 x 0.9 = 4320VA
20 x 400 x 0.9 = 7200VA
20 x 25 x 0.9 = 450VA
2x 75 x 0.9 = 135VA

Total VA = 12kVA
12 x 1.25 = 15kVA

Suitable UPS - 20kVA

This example shows that a 20kVA rated UPS would be more than adequate for this business setting allowing expansion room for extra devices, whilst running the UPS at around 75-80% of its capability.

To avoid doing all these calculations manually there are online calculators provided by the leading UPS manufacturers, that let you input the wattage, voltage or VA figures and required runtime to help you select the correct UPS. Click here to access the APC calculator.

Battery Runtime

This is the amount of time you want the UPS to keep equipment operating in the event of a power failure. This depends on the nature of the equipment, but in a mission critical business, runtime may need to be quite substantial to allow not only shut down of devices, but maybe in a specific order to ensure no processes are interrupted unexpectedly. Smaller UPS will have a single battery installed that is replaceable but not expandable or upgradeable, whereas larger UPS (usually rackmount ones) will offer extended runtime modules. These are essentially extra batteries mounted in additional rackmount chassis that sit under the main UPS unit.

UPS units that support extended runtime modules offer greater flexibility, as fixed single battery versions will provide a fixed runtime, so the only way to increase this is to go to a higher rated VA UPS. Extra batteries allow you to increase runtime without having to upgrade the VA rating, making it more cost effective overall.

Most UPS brands will provide a runtime graph for each model showing the expected runtime as the load increases. High-end UPS’s will show multiple lines, indicating how the run-time increases when one or more extended runtime modules are added.

Key on graph Configuration
B UPS + 1 extended runtime module
C UPS + 2 extended runtime modules
D UPS + 3 extended runtime modules
E UPS + 4 extended runtime modules
F UPS + 5 extended runtime modules
G UPS + 6 extended runtime modules
H UPS + 7 extended runtime modules
1 UPS + 8 extended runtime modules

Graphs like this are particularly useful if you have spare capacity on your UPS and want to know how the runtime will be affected by adding more load - either more devices, or upgrading some devices. They will help you know when more battery power is likely to be needed to maintain the runtime status quo you have.

UPS Network Management

Many UPS models designed for business have the ability to be managed and monitored over a network. They will come will either a management card installed or have an empty bay for one to be fitted.

Installing a network card can prevent having to dispatch technicians to remote locations if a problem occurs, and offers many management functions such as the ability to customise shut down and reboot of connected equipment and UPSs. It also allows you to identify problematic trends before they escalate or export the data log for analysis. Furthermore, real-time event notification minimises response times and enables IT Administrators to reduce mean time to repair, improve efficiency - thus maximising uptime.

Management software will also provide greater control over large environments. Working in conjunction with the network management card it protects the physical and virtual IT environment from threats to IT availability. Software like this is scalable in its nature so any architecture can be supported including a virtually unlimited number of client systems. Most management software is easily configurable via a browser interface and will support single, redundant or parallel UPS arrangements. Some software may be provided with the UPS but more functionality will be supported by purchasing higher-end versions.

UPS Accessories

With a large infrastructure deployment comes more complexity in power connections and wiring especially within a datacentre environment. Additional accessories keep connections to the UPS uncluttered, whilst extra sensors can provide additional data as to the rack surroundings rather than just monitoring the power source.

Power Distribution Units

PDUs or ePDUs if network connected, provide better power control from a UPS within a rack environment. Not only do they keep cabling neat, they offer monitoring ability and can even be metered if billing is being conducted in a datacentre.

Rack Cabinets

Even in a smaller office a rack cabinet provides a secure environment for UPS to be housed along with their connected servers, storage appliances and network hardware. They also work to keep cabling simple and clear and stop unauthorised users from accessing the business infrastructure. Cabinets can be configured to a range of heights - typically 14U - 47U, and with a variety of sides, shelves and mounts for PDUs and the like.

Environmental Monitoring Probes

This is a connectivity device that enables you to collect temperature and humidity readings from around the UPS and monitor the environmental data remotely. When temperature and humidity values exceed user-selectable limits, the event is logged in the UPS or ePDU event history log. Additional monitoring in this way allows for greater insight as to tenets that may affect the UPS and the rack cabinet components.

Professional Services

With many large infrastructure installations it may be necessary to have the UPS connected to the building power supply by professional prior to all the internal PDU and rack connections being configured. Scan offers a range of installation and configurations services to suit all types of UPS deployment.

Time to Choose

If you would still like some advice on sizing or choosing a UPS, don’t hesitate to contact our friendly advisors on 01204 474747 or by contacting [email protected].