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The Importance of a UPS

Jan. 25, 2010
David Stahl

In light of the recent tragic events in Haiti, it might be a good time to review some of the requirements for a well designed Uninterruptible Power Source (UPS) to be included in all of our critical network installations. As a CCNA, we are called upon to help maintain the continued operation of networks during any type of power outage caused by either supplier failures or what is often referred to as “Acts of God,” such as tornados, hurricanes or, in this case, a 7.0 earthquake.

After the devastating earthquake in Haiti, it became obvious that the country had lost most of its ability to provide any type of communications, either within the country or with the rest of the world. This blackout covered all of the most commonly used media, including the Internet, telephone, or radio. Although there were isolated instances of messages getting out, Haiti was essentially isolated, even though surrounded by neighboring countries and possible first responders.

Although we are usually only faced with incoming power source problems, they can, by themselves, bring down any normal network operation. Depending on where we live, we normally refer to our power sources as coming from household power, household electricity, power lines, domestic power, wall power, line power, AC power, city power, street power, and grid power. No matter what we call the “power source”, the loss of any normal supply can leave us with dead equipment. It is important to understand the most commonly used terminology when discussing UPS capability.

A UPS is usually implemented through the use of a battery backup. It is an electrical apparatus that provides emergency power to a load when the input power source fails. A UPS differs from an auxiliary/emergency power system or standby generator in that it provides instantaneous or near-instantaneous protection from input power interruptions. It does this by means of one or more attached batteries and associated electronic control circuitry. The downside of a battery-implemented UPS is that batteries have a maximum charge and can only provide an on-battery runtime of a relatively short period. These backup times usually range from five to fifteen minutes, which are typical for the most commonly used units. This period provides sufficient power to last until an auxiliary power source is brought on line, or the protected equipment is properly shut down. As such, a UPS is not designed to provide continuous operation until the main power source is reinstated.

While not limited to protecting any specific type of equipment, a UPS is typically used to protect computers, data centers, telecommunication equipment, or other electrical equipment where an unexpected power disruption could cause anything from a network outage to actually causing injuries, fatalities, serious business disruption, and/or data loss. UPS units range in size from units designed to protect a single desktop computer without a video monitor, which typically requires around a 200 VA rating, to large units powering entire data centers or buildings.

Even though the primary role of any UPS is to provide short-term power when the input power source fails, most UPS units are also capable of correcting other common utility power problems.

  • Total Loss of Input Voltage - A power outage, which is also known as a power cut, power failure, power loss, or blackout, is usually considered to be a short- or long-term loss of the electric power to an area. There are many causes of power failures in an electricity network, including: faults at power stations; damage to power lines; substations, or other parts of the distribution system; a short circuit; or even the overloading of electricity mains.

  • Power Surge or Spike - In electrical engineering, spikes are defined as fast-or short-duration electrical transients in voltage. They can be voltage spikes, current spikes, or transferred energy spikes in an electrical circuit. Fast, short-duration electrical transients, or over-voltages in the electric potential of a circuit, are typically caused by lightning strikes, tripped circuit breakers, and power transitions in other large equipment on the same power line.

  • Power Sag - A power sag is defined as either a momentary or sustained reduction in input voltage. A brownout or sag is a drop in voltage in an electrical power supply. The term “brownout” comes from the dimming experienced by lighting when the voltage sags.

  • Single Points of Failure - In large business enterprises, where reliability is of great importance, a single huge UPS can also be a single point of failure that can disrupt many other systems. To provide greater reliability, multiple smaller UPS modules and batteries can be integrated together to provide redundant power protection that is equivalent to one very large UPS.

Many computer servers offer the option of redundant power supplies, so that in the event of one power supply failing, one or more other power supplies are able to power the load. This is a critical point. Each individual power supply must be able to power the entire server by itself. Redundancy is further enhanced by plugging each power supply into a different circuit and to a different circuit breaker.

Redundant protection can be extended further by connecting each power supply to its own individual UPS. This provides double protection from both a power supply failure and a UPS failure, so that continued operation is ensured. This configuration is also referred to as 2N redundancy. If the budget does not allow for two identical UPS units then it is common practice to plug one power supply into mains and the other into the UPS.

Through experience, you will note that laptops are not usually protected with a UPS system since they all can function with internal battery power. Of course, the amount of runtime depends upon the type and size of the battery provided.

In my next post, I will discuss some of the most frequently used UPS technologies.

Author: David Stahl