There are many possible physical security threats associated with electrical power supply. A few examples, and ones you may already be familiar with, include :

  • Blackout:  a complete loss of power.
  • Sag or Brownout:  a decrease in voltage levels, usually of short duration but may last anywhere from fractions of a second to hours.
  • Surge: a short-term increase in the level of voltage, generally lasting a fraction of a second
  • Spike:  an instantaneous surge causing a tremendous increase to levels of voltage, usually lasting no longer than one-millionth of a second1.

In order to address these threats to physical security, a secure electrical system for computing equipment must possess the following properties:

  1. Dedicated Circuits
  2. Physical Access Control must be implemented for:
    • Master Circuit Breakers
    • Transformers
    • Power Distribution Panels and Feeder Cables
  3. Emergency Power Off Controls must be installed and accessible by the personnel on-duty
  4. Voltage Monitoring/Recording and Surge Protection should be in place

Ensuring Computer Availability through a Backup Power Supply
To ensure that your computer system remains available for use in spite of power supply threats, the power supply has to be made “fault tolerant” through the use of a Backup Power Supply. There are three ways to achieve this:

  1. Alternate Feeders
  2. Emergency Power Generator
    If using alternate feeders is not feasible, an emergency power generator should be considered as an alternative for mission critical operations. However, this security measure is very costly to maintain and operate. It is advised that a detailed analysis be performed in order to justify the high cost of this security option.
  3. Uninterruptible Power Supply (UPS)
    UPS provides just enough time for the computing system to back up data and shutdown before electrical power completely fails. UPS requires regular testing and maintenance work to ensure proper operation.  Additionally, UPS involves the use of hazardous hydrogen gas.

In addition to computing equipment, Backup Power Supply is also needed for the following vital systems:

  • Lighting
  • Physical Access Control Systems
  • Fire Protection Systems
  • Communications Equipment
  • Telephone Systems
  • HVAC

1Source: University of Connecticut Computer Center (1997), Electrical Disturbances, Available from: [Accessed 20 March 2008].