Emergency Power vs. Uninterruptible Power – There is a Difference

A common misconception is that emergency power and uninterruptible power are the same; however, emergency power is not necessarily uninterruptible, and uninterruptible power may not provide the duration of power required during power outages. Both forms of back-up power may require significant up front and long-term costs, but understanding the difference between the two systems and  ensuring that you have the correct amount of capacity, duration and availability can reduce unnecessary costs.

Two critical questions to consider are:

  1. What will happen to your equipment if your facility experiences a power outage?
  2. How long does your equipment need to operate upon loss of normal power?

Traditionally, emergency power is provided by on-site generators via automatic transfer switches. These systems are capable of providing emergency power to the equipment for hours (or even days) as long as the fuel source to the generators is available. However, connected loads will experience power interruptions after loss of normal power until the generators start and, depending on the type of transfer switch employed, another interruption during the transfer from generator power back to normal power.

Alternatively, uninterruptible power supplies (UPS) prevent the connected loads from experiencing power interruptions by using either battery or fly-wheel energy to supply the loads during a normal power outage. The duration which the UPS can supply the load during normal power outage is limited by the size and quantity of batteries or fly-wheels installed-typically limited to only seconds or minutes.

If the critical equipment requires back-up power only for an orderly shutdown, an uninterruptible power supply may be the more economical solution. On the other hand, if the equipment needs to continuously operate throughout an extended normal power outage, and the equipment can withstand a ten-second power outage or longer, a generator and automatic transfer switch solution may be the more appropriate and economical solution. Typically, the installation of critical technology equipment requires a combination of these two solutions.

Asking the right questions up front helps to ensure that the appropriate solution is selected to meet the operational requirements, budget and long-term operation and maintenance goals for the facility.

If you would like additional information regarding the capabilities and differences between emergency and uninterruptible power system, please do not hesitate to contact Jon B. Slagel, PE at (717) 845-7654 or jbs@ba-inc.com.

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