Business UPS Buyers Guide

An Uninterruptible Power Supply (UPS) is a device that sits between the building’s power source and your IT infrastructure. Its job is to ensure the servers, storage arrays and network switches receive a consistent and clean power supply, whilst also protecting them from power surges and power failures. A surge could damage components within any system and a failure could interrupt data being saved on any device, resulting in errors. The more mission-critical a system is, the more it should be power protected by a UPS.

This guide will take you through how a UPS works, common features and the factors you should consider when looking to purchase one for your organisation.

How a UPS Works

A UPS is a device that regulates mains power passing through it and provides emergency power when the input power source, typically the utility mains supply, fails. A UPS differs from an auxiliary or emergency power system or standby generator in that it will provide instantaneous or near-instantaneous protection from input power interruptions by means of one or more attached batteries. The battery runtime of most UPSs is relatively short - 5 to 15 minutes being typical - being sufficient to allow time to bring an auxiliary power source online, or to properly shut down your servers and other infrastructure hardware.

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, instructing them to shut down in a controlled and ordered manner.

Types of UPS

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. Rackmount UPS devices typically allow for more connections and offer greater expandability when it comes to battery runtime.

Tower UPS

Rackmount UPS

Aside from form factor, there are three main types of UPS - Offline or Standby UPS, Online UPS and Line Interactive UPS. Offline / Standby UPS is the most basic out of the three, providing only 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 in that 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.

A Line Interactive UPS has a similar design to an Offline / Standby UPS, but with properties of an Online UPS 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. The three types are summarise below:

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 requirement and redundancy. Correctly sizing a business UPS is crucial as it will not power all the connected infrastructure in the event of a failure if the battery capacity is too small. To calculate the total power draw for the combined critical load that needs protecting, you should look at manufacturer specs, equipment labels or technical manuals to provide the information on volts, amps and power consumption in watts, that you’ll need - then follow these steps:

1. List the amps (A) & volts (V) values

Make sure to include all devices you want to protect. For example - server(s) or storage device(s), network switch(es), PCs and monitors.

2. Multiply V by A to get VA for each device

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 all VA values together to get a total

Then multiply this total figure by 1.25, in order to factor in a degree of future growth and / or system expansion.

4. Use the final VA figure to select a UPS

All UPS are rated using either VA or kVA figures (if over 1000VA) - always aim for around 75-85% of total UPS VA rating for most stable performance.

A typical example for a mid-sized business may be as follows:

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
Optimal - 20kVA

This example shows that a 20kVA rated UPS would be adequate for this set-up, whilst running the UPS at around 75% of its capability.

To avoid doing these calculations manually there are online calculators provided by the leading UPS manufacturers, that either let you input the wattage figures if you have them, or select devices from a list provided. 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 (ERMs). These are essentially extra batteries mounted in additional rackmount chassis that sit under the main UPS unit.

If you are considering using PoE switches in any part of your network then you should check the power draw of the devices you want to connect and ensure the class of switch you choose will support the number and type of devices you require. You should also check that each device is capable of being powered by PoE.

load increases. High-end UPS’s will show multiple lines, indicating how the run-time increases when one or more ERMs are added.

Key on graph	Configuration
A	UPS
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 Accessories

High end rackmount UPS can have a number of additional features enabled if accessories are added during configuration. Examples are summarised in the tabs below.

Network Management

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. It also allows you to identify problematic trends before they escalate and export a 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.

Ready to buy?

Browse our range of UPSs:

TOWER UPS RACKMOUNT UPS UPS ACCESSORIES

Alternatively, if you have any further questions you’d like answering about business UPS, don’t hesitate to call one of our friendly advisors on 01204 474747 or by contacting [email protected].