Power/surge Protection Guide.
This article is an excerpt from a series of articles published in Practical-Home-Theater-Guide.com By: Andrew Ghigo
Unfortunately, there is a lot of misconception surrounding the use of surge suppressors. For many, it is as if once they plug one of these devices across the line, all their equipment is totally secure! This is not the case.
This article discusses the use of surge suppressors as power protection devices. It also identifies a number of important issues one needs to be aware of when working with surge suppressors. One cannot appreciate the benefits associated with the use of power protection devices without first having an understanding of what constitutes the real problem.
The AC power that flows into our homes, to feed sensitive and expensive home theater equipment, is dirty and dangerous. Surely, it is fine for lamps, drills, heaters, etc, but not for sensitive home theater audio and video systems. Power spikes on the AC line resulting from power usage patterns around the neighborhood, may have a damaging effect on AV gear. Anything that shares your power line back to the power company's main junction - industrial equipment, streetlights, a neighbor's home appliance, etc - can pollute the AC supply.
AC power is not the only source of high voltage surges. Anything that connects your gear with the outside world can carry surges into your system. In particular, lightning strikes hitting overhead power cables, cable TV and telephone lines, can result in dangerous surges down the interconnecting cables - through direct hits or through induced current - that will surely spell disaster in an instant.
Radio Frequency Noise:
Add to all this even more distortion caused by radio frequency interference (RFI), from radio and TV stations. Every copper line in your house acts like an antenna, picking up radio and TV signals, and adding them to the AC line. Seen on an oscilloscope, the AC line current would appear clogged with noise and electronic pollution that degrades audio and video gear performance.
The devastating effects of a voltage spike or surge depends mainly on:
1. Peak voltage reached during the surge
2. Energy level contained within the surge
3. The duration of the over-voltage
4. Rise-time, i.e. the time it takes for the surge voltage to reach its peak.
Engineers usually divide brief but extremely dangerous over-voltages in two categories:
1. Spikes or transients where the surge duration is a maximum of up to one microsecond (one millionth of a second), and
2. Surges when the duration lasts for up to a few milliseconds (one millisecond is equal to one thousandth of a second).
In an attempt to minimize voltage fluctuations as a result of in-house electrical appliances, many home theater enthusiasts install separate power lines from their electrical mains consumer unit, to drive home theater equipment. This helps keep large current-drawing appliances like furnaces, air-conditioners, etc. from “stealing” power from your electronics.
Surge Suppressors – A First Line of Defense
All home theater equipment should be equipped with at least some form of surge protection. Surge suppressors represent the most basic form of power protection – a first line of defense for all sensitive electronic gear.
Keep in mind that a surge in the ac voltage or a lightning strike, could lead to disaster - turning expensive gear into a smoking heap of plastic and metal. Investing in a suitably rated surge protector is surely a lot cheaper than having to replace your expensive home entertainment electronics.
The large selection of surge suppressors available on the market at an even wider range of price levels, make the whole process of selecting an appropriate protection device far from simple. Many of these surge suppressors would look the same to a non-technical person - with hardly anything that distinguish the cheapest from the best.
In their simplest form, surge suppressors often come as a surge protected multiple-outlet power-strip. One such typical inexpensive device is the Monster Cable MP AV600 Power Strip; it comes with a 555-joule rated surge suppressor.
The joule rating is a measurement of the energy absorption capability of surge protective devices. More on surge suppressor ratings later; for the time being, it is sufficient to note that a 555-joule rating indicates moderate surge suppression capabilities.
How Surge Suppressors Work
The basic operational principle behind surge suppressors is to clamp high transient voltages while absorbing this potentially destructive energy. This energy is then dissipated in the form of heat - thus protecting vulnerable circuit components and preventing system damage.
In the event that the surge lasts for several milliseconds, the process may also cause enough current to trip the house circuit breaker, or blow the equipment fuse, thus protecting your gear.
Surge suppressors usually make use of a mix of components to suppress voltage spikes on the line. However, the mostly used component in surge protection circuitry is the Metal Oxide Varistor (or MOV).
A Metal Oxide Varistor is an inexpensive yet super-fast acting device designed to create a short circuit across the line if the voltage across its terminals exceeds the breakdown point of the MOV. In the process, it shunts or diverts the surge current to neutral or ground.
At the breakdown point, the resistance of the MOV decreases from a normal 'very high level' (thousands of ohms) to a very low level (a few ohms).
The transition from a high impendence state to practically short circuit, takes place within just a few nanoseconds - typically <15ns. A nanosecond - ns or nsec - is equal to one-billionth (10-9) of a second.
In comparison, a conventional ‘fast-acting’ thermal-magnetic circuit beaker would require at least some 15-milliseconds to 150-milliseconds to operate – 1,000,000 times slower than the average surge suppressor!
In these circumstances, the conventional circuit breaker is too slow to provide some form of protection to sensitive electronic gear.
The MOV is not the only surge protection component – gas-tube surge arrestors, avalanche diodes (similar to power zener diodes), and reactive type passive circuitry using inductors and capacitors, all possess the desired electrical properties required to dampen a transient behavior.
However, none of these devices does represent the perfect surge suppressor. Some lack speed, while others – like avalanche diodes – though extremely fast acting, do have a limited energy absorption capacity. For this reason, commercial surge protection devices combine several of these technologies arranged in multiple stages, to prolong surge suppressor life and improve response times.
Surge Suppressor Ratings
This discussion will not be complete without highlighting a few of the most important parameters that define the capabilities of a surge suppressor; these are the UL listing, voltage rating, peak surge current, and power handling.
Peak Surge Current:This represents the maximum transient current that the suppressor can handle during a surge.
If you are applying surge suppression only at the point-of-use - in other words, you are not making use of additional surge protection at the point of entry of your AC mains supply - then you need to look for a peak current rating of 55,000 amperes or higher.
Joule Rating:Also referred to as ‘Energy rating’, this is a measurement of the energy absorption capability of the surge protection device. Typical values may vary from 500 to 3000 and over. The higher the joule rating, the better is the surge suppressor capability to absorb energy spikes on the line.
Performance:Remember that the performance of surge suppressors degrades with each surge absorbed. The problem here is that the rate of degradation is totally unforeseen due to the unpredictable nature of the surge. Surge rise time, peak voltage, energy level, and duration, all have a varying effect on surge protection circuitry.
In some cases, a surge may have a higher energy level than the suppressor can handle, leading to the destruction of the suppressor and zero protection against possible future surges.
To minimize this risk, top-quality power protection gear would normally make use of over-rated components in protection circuitry - thus allowing multiple surges to take place without any damage to the equipment.
Surge Suppressors are not lightning protection devices;
Surge suppressors can provide adequate protection from 'normal' surges on AC power lines. When it comes to protection against lightning strikes, it is a completely different story. Fortunately, they are rare. However, no surge protection device can offer you the required level of protection in this respect.
The unpredictable nature of a lightning strike – together with the extremely high energy level released in the process - is such that no commercially available system will offer 100% protection from a direct lightning strike on your home.
Preferably, whenever possible - try to disconnect all your gear from the AC supply during a thunderstorm. Disconnect also any telephone line and cable/satellite/outdoor TV antenna inputs – thus isolating your equipment from the outside world.
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