APC – 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 on drive.


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.

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eBC Guide to Improving Usability

Writing good copy for your web pages is extremely important not only for users but also for search engines. Fortunately for us there is no conflict in writing for users or search engines and if your copy provides the information needed by users then it will also provide the information needed by the search engines.

The practical aspects of good copy are well known thanks to many usability studies, and if you pay attention to the following for all your pages you will be doing better than 99% of websites.

1. Length
There is no fixed requirement for the amount of text on a page. Some pages may require only 150 words others may require 800 or more. Be succinct and use as few words as possible, at least half of what you would use for conventional writing.

2. Keywords
Include your keywords of course but do not worry about the number of times they appear on the page (see Keyword Density). Just write naturally and your keywords will occur in the right places and at the right frequency.

3. Grammar
Good grammar is important. Write in the active voice not the passive. If you are not sure of the difference between the active and passive voice there is a good explanation here at the Purdue University Online Writing Lab.

4. Spelling
Users who are poor spellers may not notice bad spelling but users who are good spellers will. Search engines are good spellers.

5. Headings
All usability studies show that users scan web pages ( ), they do not read them word for word. You should make liberal use of headings and sub-headings (h1, h2, and h3) so that the users’ attention can be drawn towards those elements of the text that is of interest to them. Also make sure that they are meaningful and not ‘clever’ like some newspaper headlines.

6. Highlighting
Use text highlighting such as bold, italic or color to assist the user in scanning the page.

7. Bulleted lists
An excellent method for capturing the users’ attention and getting across information in a concise manner.

8. Paragraphs
One idea, one paragraph. Usability studies show that if users are not ‘captured’ by the first few words of a paragraph they will move to the next (or hit the back button of course). One idea per paragraph ensures that users will not miss an idea by skipping paragraphs as they scan the page.

9. Sentences
Keep your sentences short.

10. Links
Embed outbound text links in your copy to improve your credibility.

11. Market Speak
All usability studies show that users hate the promotional writing style with boastful claims often used by the marketing profession. Web users want to read the straight facts and credibility goes out the window when they see marketing hype.

12. Vocabulary
Familiar words and not jargon.

13. Acronyms
If you have to use an acronym or abbreviation make sure it is understood by every user and define it on the page.

If you are not an English major (like most of us!) then the Guide to Grammar and Style ( ) or the Economist Style Guide ( ) can be extremely useful.

Additionally, Usability guru Jakob Nielsen has some useful advice on Writing for the Web ( ) and using ‘old’ words ( ).

Reprinted ( ) with permission by SEO Expert Michael Duz ( ). Michael Duz is a researcher in the field of e-marketing and search engine optimization whose organization has many well known corporate clients.

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