2 cissp ® Official Study Guide Eighth Edition

Utilities and HVAC Considerations
Power supplied by electric companies is not always consistent and clean. Most electronic 
equipment demands clean power to function properly. Equipment damage from power 
fluctuations is a common occurrence. Many organizations opt to manage their own power 
through various means. An 
uninterruptible power supply (UPS) 
is a type of self-charging 
battery that can be used to supply consistent clean power to sensitive equipment. A UPS 
functions by taking power in from the wall outlet, storing it in a battery, pulling power 
out of the battery, and then feeding that power to whatever devices are connected to it. By 
directing current through its battery, it is able to maintain a consistent clean power supply. 
This concept is known as a double conversion UPS. A UPS has a second function, one that 
is often used as a selling point: it provides continuous power even after the primary power 

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Implement Site and Facility Security Controls 
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source fails. A UPS can continue to supply power for minutes or hours, depending on its 
capacity and how much power the equipment attached to it needs. The switching from 
power grid to battery-supplied power occurs instantaneously with no interruption of power 
supplied to the equipment.
Another form of UPS is the line-interactive UPS. This type of system has a surge pro-
tector, battery charger/inverter, and voltage regulator positioned between the grid power 
source and the equipment. The battery is not in-line under normal conditions. If the grid 
fails, the power is pulled from the battery inverter and voltage regulator to provide uninter-
rupted power to the equipment.
A battery backup or fail-over battery is not a form of UPS as there is usually a period of 
time (even if just a moment) of complete power loss to the equipment as the grid source of 
power fails and a switching event occurs to retrieve power from a battery.
Another means to ensure that equipment is not harmed by power fluctuations requires 
use of power strips with surge protectors. A surge protector includes a fuse that will blow 
before power levels change enough to cause damage to equipment. However, once a surge 
protector’s fuse or circuit is tripped, current flow is completely interrupted. Surge protectors 
should be used only when instant termination of electricity will not cause damage or loss to 
the equipment. Otherwise, a UPS should be employed instead.
If maintaining operations for a considerable time in spite of a brownout or blackout is 
a necessity, onsite electric generators are required. Such generators turn on automatically 
when a power failure is detected. Most generators operate using a fuel tank of liquid or gas-
eous propellant that must be maintained to ensure reliability. Electric generators are consid-
ered alternate or backup power sources.
The problems with power are numerous. Here is a list of terms associated with power 
issues you should know:
■
Fault: 
A momentary loss of power
■
Blackout: 
A complete loss of power
■
Sag: 
Momentary low voltage
■
Brownout: 
Prolonged low voltage
■
Spike: 
Momentary high voltage
■
Surge: 
Prolonged high voltage
■
Inrush: 
An initial surge of power usually associated with connecting to a power source, 
whether primary or alternate/secondary
■
Noise: 
A steady interfering power disturbance or fluctuation
■
Transient: 
A short duration of line noise disturbance
■
Clean: 
Nonfluctuating pure power
■
Ground: 
The wire in an electrical circuit that is grounded
When experiencing a power issue, it is important to determine where the fault is occur-
ring. If the issue takes place outside your meter then it is to be repaired by the power com-
pany, whereas any internal issues are your responsibility.

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