Home Toys Article
- April 2005 -
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Power Protection in the Home Theater
The use of power line conditioners, surge suppressors, and ac regenerators, surely represents a most effective insurance policy for your expensive home theater gear.
Many do realize the need to invest in some sort of power protection. In particular, the use of surge suppressors to guard expensive equipment from damaging voltage spikes is a most common form of power protection in the home theater.
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. Selecting an inappropriate surge suppressor leads to inadequate protection. Many would soon find at their own expense that inadequate protection is practically equivalent to no protection at all! Why is there the need to invest in Power Protection?
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:
Engineers usually divide brief but extremely dangerous over-voltages in two categories:
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.
Nevertheless, this is not the ultimate solution!
The use of a separate power feed for your electronics will not prevent power line distortions from coming into the house. Similarly, it will not block noise resulting from RF pick-up, or from electrical appliance within the home. Even more so, it will not provide the required protection against dangerous power surges on the AC line.
The best way to stop power surges, block noise, and correct power distortions, is to make use of appropriate ac regenerators and power line conditioners equipped with surge suppressors. These should be designed to meet the specific needs and power demands of your AV home theater gear.
Obviously, there is an expense to power protection, but metaphorically speaking - it is an ounce of prevention that can save you a big headache down the road!
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.
More expensive units such as the Monster Cable MP HTS800 Home Theater PowerCenter HTS800, come with a higher joule rating; the HTS800 is a 1665-joule rated surge suppressor.
These devices would normally incorporate additional surge protected connections for the phone line and the coax TV input; some units include surge protected LAN connections as well.
In this manner, anything that interconnects with your equipment would have to go first through the surge protection circuitry within the power-strip.
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.
IEEE 1449 Underwriters Laboratories Listing: Referred to as 'UL 1449' or simply 'UL listing', represent a set of specifications that determine if a surge suppressor is safe during use.
Updated in 1998, the UL 1449 second edition became more stringent on safety issues. Further more, labeling of surge suppressors shifted to an aluminized label with an embedded hologram to guard against forgeries.
Ensure that the selected surge suppressor is labeled as 'UL-listed transient voltage surge suppressor (TVSS) 2nd edition'.
A UL-listing as 'power tap' is not sufficient. A UL-listed TVSS does not imply that it will protect your equipment from surges, but rather that the surge protector is not likely to pose any personal hazard to you during use e.g. through electrocution, fire, etc.
Operating Voltage: The lower the voltage rating of a surge suppressor, the more effective protection the surge suppressor will provide, however…
The voltage rating has to be in line with the respective application. If a surge suppressor is going to be used across the AC line, then the voltage rating of the suppressor has to take into account that the 120 volts ac in the US, (230/240 volts in Europe), represents the root means square (RMS) value rather than the peak.
In this case, the chosen suppressor voltage rating should allow the normal peak AC voltage to exist across the line. Peak mains AC voltage is 1.414 times higher than the specified RMS value.
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.
Designed properly, surge suppression devices can work over-and-over again, but...
A Word of Caution
Do not take surge suppression devices for guaranteed. Beware of cheaply made power line conditioners and other protection gear. Some surge suppressor components used in these devices are typically a one-time use only. This means that your system may end up completely unprotected after a surge.
Quality: The quality of a surge suppressor is reflected in the price of the protection device, but not only. Check the joule rating of the surge protector to get an indication of how much damaging energy the suppressor can handle. The bigger the joule rating is, the better. Try to go for at least a 1,000-joule rated device - preferably more.
Keep in mind however that unlike the UL-1449 Listing, there is no standardized testing methodology to determine the energy rating of a surge suppressor. Hence, do not rely on the joule rating alone - look also at the built-up quality and in particular, at the product warranty on offer.
Warranty: In addition to the standard product warranty, some manufactures also offer a 'Connected Equipment Product Warrant'. This is normally in the region of several tens of thousands of dollars.
Connected equipment warranty basically means that the manufacturer will replace up to the value of the warranty - worth of your equipment - if it is damaged by an over-voltage condition. This applies as long as the protection device is used in accordance with the manufacturer's instructions and within the terms of the warranty period.
A longer product warranty period and a higher connected equipment warranty value reflect a higher level of confidence on part of the manufacturer that the surge suppressor can protect your expensive home theater gear.
Try to go for surge suppressor devices that come with at least a 5-year product warranty period, and a minimum of $10,000 (preferably $25,000), connected equipment warranty.
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.
However, there is even more that one can do. In areas where lightning strikes are common, homeowners may want to invest in an old-fashioned grounded lightning rod on their roof. This offers the best protection you can get.
Personal safety: Ensure that your surge suppressor is clearly specified as UL listed Transient Voltage Suppressor (2nd edition). This will reduce the risk of personal harm from fire or electrocution especially during a surge. At the same time, keep in mind that a UL-listed device does not guarantee that it will protect your equipment.
More information on power protection issues in the home theater is available at Practical Home Theater Guide. Topics covered include - power line conditioners, ac regenerators, and surge suppressors. Included, there is also a short article that examines the possible use of inexpensive computer-grade uninterruptible power supplies, as part of a home theater power-protection solution.