8.10
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Network Power Supply Issues: Power Line Problems
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8.10.1
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Power problem classifications
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There
are three wires in a power cable, and problems that occur in the cable are
labeled according to the particular wire(s) that are affected. If a
situation exists between the hot and neutral wire, this is referred to as a
normal mode problem. If a situation involves either the hot, or
neutral wire, and the safety ground wire, it is referred to as a common
mode problem.
As shown in the figure,
the explanation of the power problem code is as follows. In the first line
the brown dot indicates that the ground wire is not connected. In line two,
the brown dot indicates that the neutral wire is not connected. In line
three, no dot is indicated, showing that the hot wire is not connected. In
the next two lines the blue and white dot indicate which lines are
reversed, and the final line indicates that the line has no power
connections problems.
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8.10
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Network Power Supply Issues: Power Line Problems
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8.10.2
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Normal mode and common mode
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Normal
mode problems do not, ordinarily, pose a hazard to you or to your computer.
This is because they are usually intercepted by a computer's power supply,
an uninterruptible power supply, or an AC power line filter. Common mode
problems, on the other hand, can go directly to a computer's chassis
without an intervening filter. Therefore they can do more damage to data
signals than normal mode problems. In addition, they are harder to detect.
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8.10
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Network Power Supply Issues: Power Line Problems
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8.10.3
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Typical power line problems
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Unwanted voltage that
is sent to electrical equipment is called a power disturbance.
Typical power disturbances include voltage surges, sags, spikes, and
oscillations. Another situation that can cause power problems is a total
power loss. ![](./810_files/image005.gif)
Surge
A surge is a voltage increase above 110% of the normal voltage carried by a
power line. Typically, such incidents last only a few seconds; however,
this type of power disruption is responsible for nearly all hardware damage
that computer users experience. This is because most computer power
supplies that run at 120 V are not built to handle 260 V for any length of
time. Hubs are particularly vulnerable to electrical surges because of
their sensitive low voltage data lines. ![](./810_files/image006.gif)
Sag/Brownout
A sag is a brownout that lasts less than a second. These incidents occur
when voltage on the power line falls below 80% of the normal voltage.
Sometimes they are caused by overloaded circuits. Brownouts can also be
caused intentionally by utility companies seeking to reduce the power drawn
by users during peak demand periods. Like surges, sags and brownouts
account for a large proportion of the power problems that effect networks
and the computing devices that are attached to them. ![](./810_files/image006.gif)
Spike
A spike is an impulse that produces a voltage overload on the power line.
Generally speaking, spikes last between .5 and 100 microseconds. In simple
terms, when a spike occurs it means that your power line has momentarily
been struck with a powerful hit of at least 240 V. ![](./810_files/image007.gif)
Oscillations and Noise
Oscillations are also sometimes referred to as harmonics, or noise. A
common cause of oscillation is an excessively long electrical wiring run,
which creates an antenna effect. ![](./810_files/image008.gif)
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8.10
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Network Power Supply Issues: Power Line Problems
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![](./810_files/image009.gif)
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8.10.4
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Sources of surges and spikes
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There
are numerous sources of electrical surges and spikes. Probably the most
common one is a nearby lightning strike. Through induction, a nearby
lightning strike can affect data lines. Utility switching operations
performed by the local power company can also trigger electrical surges and
spikes. Other sources of surges and spikes can be located inside your
school, office, or building. For example, when equipment such as elevators,
photocopiers, and air conditioners, cycle on and off, they create momentary
dips and surges in power.
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8.10
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Network Power Supply Issues: Power Line Problems
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8.10.5
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Surge and spike damage
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A spike
or a surge can wreak havoc on any type of sensitive electronic equipment,
including networking devices. Consequences of electrical surges and spikes
can be severe. Possibilities include the following:
- lockups
- loss of memory
- problems in retrieving data
- altered data
- garbling
Protection products can
save your data equipment from damage caused by direct contact with
lightning, power lines, or electrostatic discharge. Primary protection
devices are designed to protect people and buildings and are usually
installed on the regulated side of a network by the local exchange carrier.
Primary protection activates when lightning strikes, power lines cross, or
when other situations that create high voltage occur, triggering the device
to divert the surge energy to ground. However, primary protection devices
do not respond fast enough and their clamping levels are not exact enough
to protect today’s sensitive electronic equipment. Secondary protection
installed behind primary protection will stop any damaging surges or
currents that get past your primary protection.
- To protect the system
equipment from surges introduced between the building entrance and the
system equipment, install the inline surge protector between those two
points and as close as possible to the equipment being protected.
![](./810_files/image005.gif)
- To protect the system
equipment from surges introduced between the system equipment and the
work area, install the inline surge protector between those two points
and as close as possible to the equipment being protected.
![](./810_files/image006.gif)
- To protect the work area
equipment that is connected to the Local Exchange Carrier (LEC),
Campus Backbone Cabling or System Equipment. If the work area
equipment operates over more than one-pair, install the inline surge
protector as close as possible to the equipment being protected.
![](./810_files/image007.gif)
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8.10
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Network Power Supply Issues: Power Line Problems
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![](./810_files/image011.gif)
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8.10.6
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Surge and spike solutions
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A
common solution to the problem of surges and spikes is the use of surge
suppressors. Theoretically, when surges or spikes come in, surge
suppressors divert them to ground. In actual practice, however, it has been
found that spot placement of surge suppressors can increase the incidence
of electrical problems. For example, if equipment is not properly grounded
when a surge suppressor channels a surge to ground, it actually elevates
the ground potential. The resulting differences in ground voltages can
create electrical current that flows in the ground circuit. Current flowing
in a ground loop can damage non-protected devices; therefore, in any LAN
installation, a good rule of thumb to follow is to protect all networking
devices with surge suppressors.
If your network is
attached to a telephone line for modem or fax use, it is important that the
telephone line be surge protected also. This is because lighting strikes to
telephone lines are not uncommon. Even lightning spikes across the
telephone lines to unplugged networking devices have been known to destroy
components. As a general rule therefore, consider the telephone line to be
part of the network. If you protect one networking device with a surge
suppressor, then you should protect all devices, including the telephone
line, in the same way.
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8.10
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Network Power Supply Issues: Power Line Problems
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![](./810_files/image012.gif)
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8.10.7
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Sag and brownout solutions
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While
surge suppressors can help resolve problems presented by surges and spikes,
they cannot prevent the occurrence of sags and brownouts. A drop in AC
power may cause only the faintest flicker of your electric lights; however,
the same drop in power can be devastating to your data. This is especially
true if you happen to be updating a file directory when a power failure
occurs. Such a brownout could cause the directory, all subdirectories, and
files along its path, to be lost.
While the threat of
power outages can be minimized by keeping current backups of all data, this
measure will not prevent the loss of working files that are open on network
computers. Every network should have some type of uninterruptable power
supply.
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8.10
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Network Power Supply Issues: Power Line Problems
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![](./810_files/image013.gif)
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8.10.8
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Oscillation solution
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The
best way to address the problem of oscillation is to rewire. Although this
may seem to be an extreme and expensive solution, it is probably the only
reliable way that you can ensure completely clean, direct power and ground
connections.
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