|  | 8.10 | Network Power Supply Issues: Power Line Problems
| 8.10.3 | Typical power line problems
Unwanted excess energy that is sent to electrical equipment that uses power, called a load, is called a power disturbance. Typical power disturbances include voltage surges, sags, spikes, and oscillations. 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. 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 affect networks and the computing devices that are attached to them. 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. 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.