PC World Business

• What is a surge protector?
• Why use it?
• How surge protection works
• Blow a fuse, not your equipment
• Insidious spikes and sags
• Line noise
• Why do we get power spikes and surges?
• What is a line conditioner?
• Not a UPS?
• What about lightning protection?
• What to look for?

Let's get this sorted right upfront: ALL electronic equipment that plugs into a wall, needs protection. Without it, your expensive home theatre, sound system, TV, entertainment centre or computer equipment will likely be damaged by the surges, spikes, sags and brownouts that afflict our electrical systems. You may not see the damage until the system fails, but it can still be there, gradually "eating away" at your electronics.

Power protection devices are most commonly called "surge protectors". Types vary, but the solution is simple. The best devices include combined surge/overload protection, power conditioning and noise/interference filtering. Let's look at how they can save you from the damage caused by unregulated mains power.

What is a surge protector?

Basically, this is a device that sits between your PC or other electronic equipment and the electrical mains (AC) outlet (ie, wall plug) and protects your equipment's power supply (and possibly communications lines) from electrical surges. Any power from the mains must pass through the surge protector to reach your gear. A surge protector regulates the current to connected equipment by either blocking or shorting to ground any "unsafe" voltage.

Usually set up in a "strip" or box form, surge protectors have several power outlets to plug into. Better versions will also have at least one data outlet to protect a telephone, fax machine or modem as these are also in danger from a nasty surge of electricity through a phone line.

Why use it?

Components in today's electronic devices (including everything from computers and entertainment systems to home appliances like microwave ovens) are smaller and more delicate than their predecessors, and thus more sensitive to fluctuations in current. Microprocessors, in particular, require stable current at the right voltage -- a nice, steady flow of 240V mains power.

Unfortunately, electrical power quality changes frequently, even hourly. Anything over the standard voltage is called a "transient" and, depending on its severity and duration, can also be called a "spike" or "surge". Even though they may be so brief that they are measured in nanoseconds (billionths of a second), they can still damage your equipment. A surge lasts three nanoseconds or more; a spike only lasts 1-2 nanoseconds but both can cause damage.

Surges, spikes and sags occur daily. Many are virtually unnoticeable, but inevitably, some stronger power pulses will cause damage -- either immediately or over a period of time.

The time before and after an outage (blackout), especially during a thunderstorm, is characterised by noticeable surges and sags, much like how tremors are felt before and after an earthquake. Even if you do not personally notice these fluctuations, your unprotected electronic equipment will.

How surge protection works

A surge protector usually works by channelling any extra voltage into the electrical outlet's "earth" or "ground" wire, thus stopping it from reaching your equipment. At the same time, it still allows the normal voltage to continue.

In the most common type of surge protector, the extra voltage is diverted by a component called a metal oxide varistor, or MOV. A MOV provides strong surge protection, but degrades each time. It may even last only once.

Another common (and cheaper) type of surge protection is provided by a gas discharge arrestor (gas tube). It uses an inert gas which only becomes conductive under a strong surge of electricity, then diverts the excess harmlessly to "ground".

Silicon Avalanche Diodes (SADs) are known for their fast response time and low voltage clamping level. Clamping voltage is the maximum amount of voltage that a surge protector will let through before it suppresses the surge by conducting electricity to the ground line. The lower the clamping voltage the better the protection. A plus for SADs is that unlike MOVs, they don't degrade with repeated surges so they last longer. But MOVs provide better strong-surge protection.

The best -- but naturally, more expensive -- surge protectors include a combination of SADs and MOVs and possibly gas tubes as well.