The Anatomy of a Power DisturbanceSurges, spikes, blackouts and brownouts...what really happens to a computer when it experiences an out-of-bounds power anomaly?
We'll use a nearby lightning strike as an example, although it is just one of countless problems that can strike a system.
Lightning strikes a nearby transformer. If the surge is powerful enough, it travels instantaneously through wiring, network, serial and phone lines and more, with the electrical equivalent force of a tidal wave. The surge travels into your computer via the outlet or phone lines. The first casualty is usually a modem or motherboard. Chips go next, and data is lost.
The utility company responds to overvoltages by disconnecting the grid. This creates brownouts and blackouts. If the voltage drops low enough, or blacks out, the hard disk may crash, destroying the data stored on the disk. In all cases, work-in-process stored in cache is instantly lost. In the worst case, password protection on the hard drive can be jumbled, or the file allocation table may be upset, rendering the hard disk useless.
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Power Event Definitions, Causes and Effects
Also known as brownouts, sags are short term decreases in voltage levels. This is the most common power problem, accounting for 87% of all power disturbances according to a study by Bell Labs.
- CAUSE - Sags are usually caused by the start-up power demands of many electrical devices (including motors, compressors, elevators, shop tools, etc.) Electric companies use sags to cope with extraordinary power demands. In a procedure known as “rolling brownouts,” the utility will systematically lower voltage levels in certain areas for hours or days at a time. Hot Summer days, when air conditioning requirements are at their peak, will often prompt rolling brownouts.
- EFFECT - A sag can “starve” a computer of the power it needs to function,
and cause frozen keyboards and unexpected system crashes which both result in lost
or corrupted data. Sags also reduce the efficiency and life span of electrical
equipment, particularly motors.
Total loss of utility power.
- CAUSE - Blackouts are caused by excessive demand on the power grid, lightning storms, ice on power lines, car accidents, backhoes, earthquakes and other catastrophies.
- EFFECT - Current work in RAM or cache is lost. The hard drive File
Allocation Table (FAT) may also be lost, which results in total loss of data stored
Also referred to as an impulse, a spike is an instantaneous, dramatic increase in voltage. Akin to the force of a tidal wave, a spike can enter electronic equipment through AC, network, serial or phone lines and damage or completely destroy components
- CAUSE - Spikes are typically caused by a nearby lightning strike. Spikes can also occur when utility power comes back on line after having been knocked out in a storm or as the result of a car accident.
- EFFECT - Catastrophic damage to hardware occurs. Data will be lost.
A short term increase in voltage, typically lasting at least 1/120 of a second.
- CAUSE - Surges result from presence of high-powered electrical motors, such as air conditioners, and household appliances in the vicinity. When this equipment is switched off, the extra voltage is dissipated through the power line.
- EFFECT - Computers and similar sensitive electronic
devices are designed to receive power within a certain voltage
range. Anything outside of expected peak and RMS (considered the “average”
voltage) levels will stress delicate components and cause premature failure.
More technically referred to as Electro-Magnetic Interference (EMI) and Radio Frequency Interference (RFI), electrical noise disrupts the smooth sine wave one expects from utility power.
- CAUSE - Electrical noise is caused by many factors and phenomena, including lightning, load switching, generators, radio transmitters and industrial equipment. It may be intermittent or chronic.
- EFFECT - Noise introduces glitches and errors into executable programs and data files.