Buying guide: power protection

Protect computer systems against damage from power surges. Here's how.

Looking for more IT advice? Post your question here, and we'll get our experts to answer.

Q. What is the difference between a power surge protector and an uninterruptible power supply (UPS)?
The primary function of a good surge suppressor is to protect your critical application (load) from multiple catastrophic "surge events" such as lightning strikes and industrial accidents over a period of several years.

SMB Buying Guide

Did you know?
There are three different types of UPS (uninterruptible power supply) available: offline, line interactive and online. UPS is most often integrated into the network environment for ease of monitoring and management.

Bottom line:
Your choice of UPS should be based on the criticality of your systems. It should be based on your sensitivity to downtime and how much it cost when your system goes down.


Emerson has an application philosophy known as a "cascaded" design that sees surge suppression equipment placed strategically throughout the infrastructure. Essentially the larger and most robust surge suppression units are located closest to the electrical grid, and then sized progressively smaller as you move (distribution board to distribution board) closer to the load.

The net result is that surges generated externally to the facility are eliminated before they can impact on any load equipment. But also importantly, internally generated surges, which can occur from lift motors, air-conditioning units or even photocopiers, are also eliminated from the system.

The primary function of a good UPS is to deliver a perfect sine wave (i.e. clean power) to the critical load regardless of the condition of the supply. This means that it will deliver clean power in a surge condition, as well as during a total loss of power or when the facility is supported by a diesel-powered generator, also referred to as an alternate power supply or emergency power supply.

Most smaller UPS have an internal battery which will deliver uninterrupted power in the event of blackout for 5 to 10 minutes at typical load. This "runtime" can be extended according to the customers requirements. UPS is most often integrated into the network environment for ease of monitoring and management.

Q. How do I know which type of UPS to buy?
There are three different types of UPS available: offline, line interactive and online. Each delivers a different level of "uptime". Offline will deal with approximately 60 percent of power quality events, which refer to anything from a surge, a glitch in the power, brown out and black out, or variation in frequency, without disruption to the load. Line interactive will deal with approximately 80 percent of power quality events without disruption to the load, while online as a standalone device will deal with approximately 99.9 percent of power quality events without disruption to the load. Different configurations of online UPS will deliver up to 99.9999 percent uptime. Your choice of UPS should be based on the criticality of your systems. It should be based on your sensitivity to downtime and how much it cost when your system goes down.

Q. What else should I look out for?
The main thing is to have a clear understanding of what you are buying. Some UPS manufacturers will try to pass off a "lesser" UPS as online or as good as online. It's a game that many vendors play. There are global references in place, such as the IEC Global Standard that defines the technology (IEC 62040-3 classification of UPS). However, this is not referenced in many cases. The IEC (International Electrotechnical Commission) is the global organization that prepares and publishes international standards for all electrical, electronic and related technologies.

This tech tip was contributed by Russell Perry, director of marketing, Emerson Network Power.

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