Copyright: Canada Hifi Magazine Thursday May 05, 2005
Reproduced with permission
When I was younger, my father always stressed to me the importance of
plugging our electronics into power bars with surge protection instead of
directly into the wall outlet. He said it would protect the electronics from
voltage surges - anything from smaller spikes to lighting storms. I thought
it was a little ridiculous. After all, how many precious pieces of
electronics have you lost to a lightning storm? Then one day the unthinkable
(to me) happened. One of my family's television sets not plugged into a
surge protector blew up during a lightning storm in my neighborhood. Well it
didn't actually blow up, it simply stopped working.
While this scenario is not common at all, electrical surges and spikes
occur in our power lines regularly. These surges and spikes can be severe
enough to damage home theater equipment (as well as other sensitive
electronics) gradually or immediately. Modern power protection equipment
ranges from the simple power bar with surge protection to a power center
that combines surge protection, line conditioning, voltage regulation and
even power backup.
As it turns out, power bars with surge protectors (also called surge
suppressors) are actually a little more complicated than first meets the
eye. Depending on what level of protection and features a power bar has it
can cost anywhere from five dollars to several hundred dollars.
First let's take a look at how your home theater can be affected by
unclean power and what to look for when choosing power bars and power
centers to protect your investment.
In a normal household and office wiring in North America, the standard
voltage is 120 volts AC (Alternating Current). Power lines are inherently
noisy and voltage surges and spikes are common. This increase in the
electrical potential energy can be caused by lightning storms, power company
load switching, short circuits, improper home wiring, blackouts as well as
power-hungry household electrical devices such as refrigerators,
air-conditioners and microwaves. These high-powered devices require a lot of
energy to switch on and turn off components like compressors and motors. An
increase of voltage which lasts for one or two nanoseconds is called a spike
and one that lasts three nanoseconds or longer is called a surge. Both
spikes and surges (also called transient voltages) can compromise the
performance of a home theater and over time can lead to premature demise of
equipment. In the worst case, these transient voltages can reach as high as
6000 volts and fry electronics instantly. Today's electronics are much
smaller and more delicate than components in older equipment and are
therefore more sensitive to current increases. Modern electronic devices can
literally fry from overheating if they receive more power than they are
designed for. For this reason it is becoming increasingly important to
protect your electronics. No power bar with surge protection can actually
save the connected components from a direct lightning strike, but the
chances of a direct strike are very rare. In a lightning storm you should
never rely on a surge protector to save your equipment. The best protection
is to unplug or turn off your power bar. A good quality power bar will not
send any electricity to the devices connected to it when it's turned off.
A standard power bar with surge protection passes the electrical current
from the wall outlet to the devices plugged into the power strip. If the
voltage from the outlet rises above 120 volts, the surge protector diverts
the extra electricity into the outlet's grounding wire. One critical
characteristic of transient voltages is that they are very quick. A device
that serves to filter out the voltage spike has to detect the spike in
nanoseconds in order to be effective. Look for surge protectors with a
response time of 1 nanosecond or less. In most surge protectors the
component that actually diverts this extra electricity is called a metal
oxide varistor (or MOV). A good power bar will usually have several MOVs.
Each MOV forms a direct connection between the hot power line and the
grounding line. Generally, an MOV consists of a piece of metal oxide
material in the middle that is joined to the power and grounding lines by
two semiconductors. These semiconductors have a variable resistance that
depends on voltage. If the voltage is below a certain level, the electrons
in the semiconductors flow in a way that creates a high resistance, not
allowing electricity to pass from the power to the grounding line. When the
voltage exceeds that level, the electrons behave differently creating a much
lower resistance. This low resistance allows the MOV to conduct a lot of
current to the grounding line. Unfortunately all MOVs eventually burn out.
In fact, one good surge can burn out all the MOVs in your power bar. When
the MOVs cease to function, the power bar simply becomes a power strip and
you may not even know it. Inexpensive power bars don't have any visible
signs that the MOVs are not working. Good quality power bars have an
indicator light that tells you whether the surge protection is working
properly.
Power surges can also reach your home theater through the coaxial cable
carrying cable television or satellite signals. A power bar in your home
theater should guard your equipment against both surges in the power lines
and surges in the coaxial cable. Most modern power bars offer both types of
protection plus a protection for telephones lines that are also susceptible
to power surges. Power bars come in varying ranges of prices, performance
and shapes. There are many different products out there from the simplest $5
power bar (or power strip more appropriately) to a several hundred dollar
rack-mountable power center that looks like a home theater component. When
choosing the right device to protect your home theater you'll have to
consider several specifications and features shared among protection
devices.
Let's take a look at the ratings you should look when buying a power bar
(or center) with surge protection that might also offer power line
conditioning .
To make sure you're buying a quality product, first check out its
Underwriters Laboratories (UL) ratings. UL is an independent company that
tests electric and electronic products for safety. Many surge protectors
made prior to 1998 are potential fire hazards. The MOVs inside them can get
very hot to the point of starting a fire during a large power surge. Look
for a label on the product that reads "UL Listed", not just "UL Approved" or
"UL Tested". Also make sure the product is labeled as a "transient voltage
surge suppressor". This means that it meets the criteria for UL 1449 and
minimum performance standards for surge suppressors. Not all "UL Listed"
power bars have surge protection.
Every surge suppressor has a clamping voltage. This is the peak voltage
the suppressor will pass to the devices plugged into it, if a spike or surge
occurs. Look for a suppressor with a claming voltage of 330 volts. Also,
make sure the device is equipped to absorb surges between any pair of the
three wires (positive, negative and ground) in an electrical circuit. These
are indicated by the symbols L-N, L-G, and N-G.
Surge protectors are marked with a Joule rating. A Joule measures how
much energy the suppressor can absorb and dissipate before it fails. The
higher this number - the better. Look for surge protectors with at least 600
joules or more. Many of today's power protection devices designed for the
home theater offer ratings between 1300 and 2000 joules.
Another rating to look for is the response time. This indicates the
amount of time it takes for the MOVs inside the power protection device to
absorb the transient voltage. As mentioned above, look for response times of
1 nanosecond or less.
Lower quality power bars with surge protection may cause as much as 20 to
30 dB of signal loss between their coaxial input and output. This can have a
tremendous impact on the quality of your cable/satellite television signals.
Look for power protection devices the have virtually no signal loss through
their coaxial surge protection.
Intermediate power products offer power line conditioning in addition to
surge protection. AC power line noise and noise generated by other
electrical and electronic devices compromise the performance of home theater
equipment. These disturbances can cause inferior picture quality flawed with
video streaking, lower resolution and video bandwidth. From the audio
perspective, power line pollution can cause dynamic distortion and loss of
peak power. Power line conditioning removes this noise from the power line
and maximizes the audio and video performance in the home theater.
More advanced power products also feature filters which deliver maximum
current to high power components (such as amplifiers) and isolate audio
equipment from video equipment. Each home theater component can add noise to
the power line that can travel through your power bar or power protection
device to other components plugged into it. Isolating audio and video
equipment ensures that noise is not transferred between the components. Some
devices even isolate analogue sources from digital sources plugged into
them.
High-end power protection and conditioning products come equipped with
voltage regulators or voltage stabilizers. Power coming from the wall outlet
does not always measure exactly 120 volts. At peak power consumption times
during the day, it probably measures closer to 115 volts whereas at night it
might be closer to 125 volts. Devices with voltage regulators constantly
measure the voltage on the power line. If the voltage dips below or goes
over a specified range (for example between 88 volts and 130 volts) a
voltage regulator will adjust the voltage to 120 volts.
Some power protection products (like APC's S10 and S15) even have battery
backup power included for times when the power goes out completely. This
will allow your home theater system to run for an additional few minutes
after the power outage and will shut down your entire system properly and
automatically. Of course a battery backup can be purchased separately as an
addition to any power protection product of your choice.
Finally, when looking for protection for your home theater, take a look
at the manufacturer's warranty as it may be a good indication of product's
quality. Usually the more the manufacturer is willing to cover the more
confident they are in their product. Of course, you should never rely on
getting the money for your damaged equipment - the warranty lists all kinds
of conditions under which you may not qualify to get this money.
Looking at the price of a device will give you an insight into what level
of protection you can get from it. As a general rule, don't expect much
protection, if any, from a power bar that costs less than $10 - most of
these are simply power strips. In the $10 to $30 range you will find basic
surge protection and few features. Power bars above $40 will offer better
protection ratings and carry additional features. Devices that cost a few
hundred dollars and more will offer line conditioning, voltage regulation
and even power backup in addition to surge protection. Consider how much
your home theater gear cost you and how little that $100 or $200 power
protection device may be compared to the rest of the equipment. You might
look at power protection equipment as in insurance policy that doesn't carry
monthly payments. If only there was something like this for cars.
