8.10 Network Power Supply Issues: Power Line Problems 8.10.1 Power problem classifications Instructor Note The definitions of normal mode and common mode electrical problems are introduced. Remember that all voltages (electrical potential differences) are measured between two points, so you must define what those two points (hot and ground; hot and neutral; neutral and ground) are when discussing potential voltage problems. 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. 8.10 Network Power Supply Issues: Power Line Problems 8.10.2 Normal mode and common mode Instructor Note Common mode problems are identified as the more serious of the two types of power connection problems. 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. 8.10 Network Power Supply Issues: Power Line Problems 8.10.4 Sources of surges and spikes 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. 8.10 Network Power Supply Issues: Power Line Problems 8.10.5 Surge and spike damage 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 8.10 Network Power Supply Issues: Power Line Problems 8.10.7 Sag and brownout solutions While surge suppressors can help resolve problems presented by sags 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. 8.10 Network Power Supply Issues: Power Line Problems 8.10.8 Oscillation solution 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.
