Copper Applications Power quality and your computer

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Copper Applications in
Electrical Area
Power Quality and Your Computer
By 
Martin Conroy 
President, CPC, Inc.
March 1999
Did you hear the one about the car that was designed to run on a PC?
Guaranteed to crash at least once a day.
Just kidding. But since you use your computer regularly, you're probably
used to the occasional crashes, hang-ups, etc. that come with the territory.
It happens, you re-boot, mutter a few words in the general direction of
Redmond, Washington, and off you go again until the next glitch comes
along.
It's usually a software problem, maybe accompanied by an ominous
message like "YOUR SYSTEM HAS PERFORMED AN ILLEGAL
OPERATION " or "INSUFFICIENT MEMORY TO RUN THIS
APPLICATION". But sometimes it's not the software's fault. It could be a
question of inadequate power quality. Power quality? Since when does
power have "quality"? It's either on or it's off, right? Well, yes and no. Back
in the dark ages BC (before computers), it usually was sufficient that the
power turned on whenever you flipped the switch. And it usually did, except
during summertime brownouts when too many people turned on their air
conditioners at the same time or after the occasional blackouts when
lightning (or some motorist) struck a pole. Other than that, electric power
quality was unremarkably adequate.
That's no longer the case, because the way we use electric power has
changed significantly. Just a few years ago, most of the electrical uses in
our homes (and in our factories and offices, for that matter) involved
lighting, electric motors and a few transformers. We still need those things
today, but we also increasingly rely on what we might call "electronic"
applications of electric power. Electronic applications include not just
computers and their peripherals, but all of the appliances, tools,
instruments, thermostats, burglar alarms, audio/video equipment, copiers,
fax machines and other gadgets that contain some form of microchip or
"logic circuits". It's those electronic gadgets that are so finicky about power
quality. The Institute of Electrical and Electronic Engineers (IEEE) even has
a name for them; they call them "Sensitive Electronic Equipment," and have
published special recommended practices to deal with them correctly.
These things simply can't tolerate the sort of lapses in power quality that
light bulbs and electric motors routinely shrug off.
Since more and more sensitive electronic equipment is finding its way into
our homes - especially as home offices become more popular - we've
prepared this article to explain the concept of power quality and how it can
affect you. We'll also explain how the proper use of copper wiring can
ensure that your sensitive electronic equipment functions properly. And, if
you're considering building a new home or thinking about re-wiring your
current one, we'll mention a few pointers that will "build in" good power
quality from the start.
Continuity, Voltage and Frequency/Waveform 
Because of the various ways we use electricity, power quality means
different things to different people. Still, there are three basic attributes that
we can use to "rate" power quality, at least qualitatively, from the point of
view of the homeowner or home office user. These attributes are:
1. The continuity with which the power is supplied,
2. The voltage seen at the point of use, and
3. The power's frequency and waveform. (We'll define these terms in a
moment.)
Continuity, or how continuous the supply is, means more than that the
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power should simply turn on and stay on whenever you flip the switch. It
means that there can be no gaps, even momentary ones, when power is
flowing. That's important because sensitive electronic equipment requires
almost total continuity, literally down to the millisecond. For example, you've
probably experienced something like this:
There's a thunderstorm brewing. Miles away, lightning strikes your
utility's power grid. Your lights flicker off and on and electric motors
hesitate. But just as quickly, everything returns to normal, except
that your computer has re-booted, the satellite TV is asking you to
reprogram its available channels, the thermostat has to be reset
and all your digital clocks are blinking "88:88".
Or maybe you've seen this situation:
Your computer is plugged into a wall outlet that also feeds your
monitor, printer, scanner, zip drive, copier and maybe a fax
machine; a typical home office setup. You hit the "Print" button and
everything shuts down because you've tripped a circuit breaker.
(Did you save your work?)
The first case wasn't your fault, the second one was. Either way, you've
experienced one form of poor power quality - an interruption - and your
sensitive electronic equipment couldn't cope. What can you do about
continuity problems? The quick-and-dirty solution is to install an
uninterruptible power supply, popularly known as a UPS, between your
equipment and the wall outlet. A UPS is essentially a battery that is
continuously charged by line power, its ac voltage suitably stepped down
and rectified to dc. The battery's dc power output is re-converted in the
UPS back to ac power by a device called an inverter, whose "synthetic" ac
power is then output to your equipment. When line power is interrupted, the
battery acts as a reservoir, providing a few minutes to a few hours of power
so your equipment can ride out the outage. There are many types and sizes
of UPS units. The better ones have built-in surge protection devices.
They're cheap insurance: UPS units that are adequate for home offices
retail for about $100-$200. If your power grid has frequent outages,
consider a conservatively rated (long runtime) UPS.
On the other hand, if you've overloaded the circuit that feeds your
computer, you should think about installing a UPS and distributing your
electrical loads by adding additional circuits. This is the correct long-term
solution to frequent circuit breaker trips. There are several benefits to
adding more circuits, but maintaining continuous power is reason enough to
give the idea some thought. The cost of the few additional yards of copper
wire and a few hours of an electrician'stime can be inconsequential
compared with the cost of lost data.
Voltage variations are another common source of problems to home
computers and other sensitive electronic equipment. Voltage variations can
be positive (higher than normal) or negative (lower). Variations can be
huge, reaching thousands of volts, but even small ones can cause
problems. Most computers can withstand variations of ±10% (±12 volts on
a 120-V circuit), although they can detect, and may be affected by, smaller
variations. The human eye can distinguish a lamp flicker caused by a ±1.5v
change in voltage, so if you can see the effect of a voltage change,
chances are good that your computer can feel it. An important point to
remember is that the computer manufacturers base their voltage range
assuming a true sine wave voltage waveform. If the voltage waveform is
flat topped or distorted, your computer may not operate within the stated
voltage range. We'll explain sine wave distortion in a moment. Let's get
back to that overloaded branch circuit we described earlier. This time, we
won't quite trip the circuit breaker.
Everything's running well. Your spouse turns on the dishwasher.
Your desk lamp dims but doesn't go out. Still, your computer hangs.
Or,
You decide to move your home office to the other end of the house
because it's quieter there. You don't add any equipment; you just
move what you have. Your equipment is now more than 50 feet (15
m) from the electrical service entrance panel. You begin to notice
that your computer doesn't work as reliably as it used to, and you
start having problems with your monitor.
The problem in these cases may be low voltage. In the first case: Switching
on a high-startup-current appliance (usually one containing a powerful
motor) will momentarily reduce line voltage in that branch circuit. Everything
else connected to that circuit would feel the reduction. In the second case:
Your standard 20-amp circuit may have reliable 120v at the electrical panel,
but after running through 50 ft of wire, what your sensitive electronic
equipment sees at the outlet is a voltage that may be reduced by as much
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as 5%. This voltage reduction (or "delta v") can have several effects:
First, low voltage can cause the dc power supplies in your
equipment (all electronic equipment has them) to run hotter than
normal.
Here we have to introduce a little algebra to explain our point. The
power (P) these power supplies draw is equal to the line voltage (E)
at which they operate (nominally 120v) times the current (I) they
draw, or P=EI. The power drawn is constant, fixed by the needs of
the equipment; so any decrease in voltage must be compensated
by a proportional increase in current. Now, the amount of heat
dissipated by the power supply (specifically, by resistive (R)
elements such as resistors, wires, etc.) is proportional to the square
of the current flow, P=I2R. Therefore, the end result of a drop in
voltage at the wall outlet is a rise in the temperature in the
equipment. At best, this excess heat is represents wasted energy;
at worst, it can shorten the equipment's life.
Second, low voltage can cause components to fail because the
increased current exceeds the components' ratings.
Power supplies in computers are usually more powerful than they
need to be because manufacturers understand that owners often
add equipment (additional hard drives, tape backups, etc.) after the
computer has been placed in service. As an incidental benefit, such
oversized power supplies can accommodate the extra current
drawn when line voltage drops. Power supplies in monitors, on the
other hand, are sized just large enough for the existing load, there
being no need to expect any later additions. High currents caused
by low line voltage can damage such power supplies.
Finally, a drop in line voltage may interfere with your computer's
operation, particularly if the computer is networked. The power
cable that supplies your outlet contains three conductors, a phase
(or "hot") wire, which usually has black, red or blue insulation; a
neutral wire, usually white, and a ground wire, conventionally green.
If your computer's plug has three prongs, the round "third" one is
the ground.
When we speak of voltage in the conventional sense, we refer to
the voltage between phase and neutral conductors. However, a
voltage can also exist between the neutral and ground conductors
at distances well removed from your house's service entrance panel
(it has to be zero at the panel because that's where the neutral and
ground conductors are joined). This neutral-to-ground voltage is
normally zero or close to it, but when the phase-to-neutral voltage
drops, the neutral-ground voltage rises. In fact, it rises by exactly
one-half as much as the drop in phase-to-neutral voltage, e.g.,
reducing the phase voltage from 120v to 110v incurs a 5-v increase
between the neutral and ground conductors.
Most desktop computers can tolerate as much as ±10% variation in
phase-to-neutral voltage, but they are quite sensitive to small
changes in neutral-to-ground voltage. This is particularly true for
newer computers whose logic circuitry may operate at less than one
volt. (Laptop computers aren't as sensitive to this situation because
they generally don't have an external ground connection.)
Moral of the story: play it safe, play it smart, use a separate circuit,
or add one, for your sensitive electronic equipment.
Positive voltage variations can be even more troubling than negative
ones. If powerful enough, they can destroy components in sensitive
electronic equipment. Such positive variations, or "transient voltage surges"
as they're called, can arise outside your home. Lightning striking power
lines is a frequent cause, as is load switching (re-routing power around the
grid) by your utility. Voltage surges can also be caused by equipment in
your home. Refrigerator motors, air conditioners, vacuum cleaners and
other electrical loads can generate voltage surges and electrical noise.
The best defense against voltage surges is to install a transient voltage
surge suppressor (TVSS) between your equipment and the wall outlet. As
with uninterruptible power supplies, surge suppressors are cheap and
widely available in a variety of styles and sizes. You may already have one:
it's the "power wand" containing about half a dozen outlets into which you
connect you computer, monitor and other equipment. Check the label to
see if it has TVSS protection. If you need to purchase a TVSS make sure it
is UL 1449 listed. This assures the product has been tested and meets
industry standards.
No amount of additional copper house wiring will protect you against
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voltage surges, although a good lightning protection and grounding system
will isolate your sensitive electronic equipment - along with the rest of your
home - from nearby lightning strikes. We'll talk about grounding and
lightning protection in a future article.
Frequency & Waveform 
In North America, household electric current and voltage alternate (it's the
"a" in ac) or switch back and forth between positive and negative poles at a
frequency of exactly 60 alternations each second. Engineers call that the
fundamental frequency; it's usually expressed as 60 cycles per second
(cps) or 60 Hertz (Hz). In most other parts of the world, the fundamental
frequency is 50 Hz.
Alternating voltage/current alternations take the form of a sine wave. That
is, if you could see the current changing over one ac cycle (which takes
1/60th of a second or 16.7 milliseconds) the shape of the alternations, the
sinusoidal waveform, would look like this:
Voltage and current begin each cycle at zero (the horizontal line), rise to a
maximum in one-quarter of a cycle, fall back to zero at the half-cycle point,
then reverse polarity and fall to a maximum negative value at the 3/4cycle
point before rising to zero again. All of this repeats every sixtieth of a
second. If you've ever touched a live electric line, the vibrating shock you
feel is this sixty-time-per-second voltage reversal.
In ordinary house current, 120 volts is what engineers call the effective 
voltage, which is actually a sort of average (the root mean square value) of
the varying voltage depicted by the sine wave. The actual peak voltage in a 
120-V circuit can be as high as nearly 170V. Except for simple things like
incandescent light bulbs, most of the electrical and electronic devices we
use today are designed for ac power that follows the sine wave curve. To
these devices, the right voltage plus a perfect sinusoidal waveform add up
to ideal power quality. By the same token, anything that disturbs either the
power's frequency or its waveform detracts from power quality, and in so
doing, reduces the ability of electrical devices - especially sensitive
electronic equipment - to operate properly.
What can disturb the frequency? Not much, so far as power supplied by the
utility is concerned. In fact, electric utilities go to great lengths to make sure
that their generators operate at precisely 60Hz and that they're all
synchronized as closely as possible. When the current produced by a
power station in Bangor, Maine is at the exact maximum point of the sine
wave, current coming out of a power station in Los Angeles - and out of
your wall outlet - is there, too.
Most frequency disturbances actually originate inside buildings. Ironically, it
is mainly the sensitive electronic equipment that is at fault. Remember
those dc power supplies we keep mentioning, the ones that power most of
our "electronic" equipment? These days, most such power supplies are of a
type (called "switched mode power supplies") that draws current in sharp
pulses rather than in a smoothly flowing sine wave. As they do so, they
echo those pulses back into the power line, where they are superimposed
on the normal sine-wave current flowing there. Other common household
sources of these erratic disturbances include:
dirty switches or relays that arc when they make or break contact;
worn dc electric motors (you know you have a problem when you
can see sparks in the commutator);
portable arc welding machines;
certain UV lights, and
many electronic fluorescent light ballasts.
Add them all up and the result is a messy waveform circulating in your
house current.
Normally, waveform disturbances are not a problem in a home-office
situation. Really serious problems arise in offices and commercial buildings
where there may be hundreds of computers, electronic lighting ballasts and
similar equipment on the same floor. The power disturbances generated by
all those switched mode power supplies can add up to wreak havoc with
computer reliability, not to mention fire hazards and other problems.
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The number of computers and peripherals installed in a home office is far to
small to cause that level of disturbance. On the other hand, there is a real
possibility that by concentrating all of your sensitive electronics on one
branch circuit, you can degrade power quality enough to provoke the
occasional electronic hiccup and crash your computer.
Harmonics 
The main cause of waveform distortion in modern "electronics"-loaded
circuits, including the ones in your home office, is an electrical phenomenon
known as harmonics. All commercial power is based on a pure sine wave
waveform (remember physics class?). The utility generates 60-Hz sine
wave power and transmits it to your home. Your home wiring distributes the
sine wave power to your wall outlet and your computer power supply is
designed to run on it. The assumption is that the power maintains the
correct sine wave shape from generation to utilization. This assumption is
not always correct. It is now understood that the very power supply that is in
your laser printer and computer can cause a distortion of the voltage
waveform, superimposing electrical jiggles that can be expressed as
multiples of the standard 60-Hz frequency, i.e., 120Hz, 180Hz, 240Hz…etc.
These jiggles are called harmonics.
The amount of distortion is measured in total harmonic distortion, or THD.
The IEEE has issued guidelines for recommended levels of THD. Generally
anything over 5% voltage THD is unacceptable.
Harmonics have created serious problems in offices that contain a high
density of computer equipment. We routinely find a high level of voltage
THD in office buildings. It far less likely that you would have a harmonic
problem in your home. However, if you have undersized wiring or
overloaded circuits, you could have this problem.
What problems do harmonics cause? The most common problem is a
flat-topping of the voltage waveform. This causes a reduction of the peak
voltage level, which in turn can starve your computer's power supply of
energy. To put it in simple terms, running your computer on a distorted
140-volt (instead of the expected 170-v) peak voltage is like running it on
about 95 volts AC. You may not see the problem, but your computer does!
It takes special equipment to measure harmonics so the problem may very
likely go unnoticed.
Thinking about Remodeling? Think Extra Circuits. 
If you're considering building a new home or thinking about remodeling your
current one, you should be aware that there a many advantages to bringing
your wiring system up to current practices. This is especially true if you plan
to add more sensitive electronic equipment (which is likely), maintain a
home office or create a local area network (LAN) to link your home
computers.
Consider this:
The National Electric Code® (NEC) governs the way we wire our homes,
offices and commercial buildings. The NEC permits up to 13 outlets on a
20-amp branch circuit, the type commonly found in homes. This limitation is
based on safety: limiting the number of outlets effectively limits the total
load (total current flow) on the branch circuit and thereby eliminating
overloading and circuit breaker tripping. Recommended practices for home
offices with a number of technology systems include:
1. Branch circuits that feed sensitive electronic equipment should be kept
separate from branch circuits that feed ordinary loads, such as lighting and
motor-driven equipment. If possible, use separate circuits for your laser
printer and the rest of your computer equipment. 
2. In older homes with two-prong, non-grounded outlets, upgrade to
three-prong grounded type circuits. The only way to correctly do this is to
run a new copper cable from the main service to the office area. Remember
that a grounded circuit is required for protection of your computer from
static electricity and power surges. Without a grounded circuit your modem
may become the ground source. 
3. Have an electrician check your main service for proper grounding. In the
past the metal water main was used to ground the service, but now many
communities are using plastic water piping. If your home does not have a
ground rod, install a 10-foot long ground copper clad rod to supplement
your home's grounding. This is cheap insurance and enhances safety. 
4. Make sure that your home's telephone and cable (CATV) are grounded
and bonded to the main electrical service ground. Without this bonding,
lightning and power surges can circulate through your computer system. In
fact your computer may be the one piece of equipment in your home that
combines power, telephone (modem) and cable (cable modem or video),
thereby becoming a path for any type of lightning surge. 
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5. Have an electrician install a main service surge protector (TVSS) ahead
of your main service entrance electrical panel. This will protect your home
from large power surges. A basic unit will cost about $ 150 installed. Make
certain that this TVSS is properly grounded or it won'twork when it has to. 
6. Use TVSS protection between the wall outlet and your computer. Use a
unit that protects the power, telephone and cable service. 
7. For additional power protection consider installing an uninterruptible
power system (UPS). Choose a system large enough for your equipment
power needs. 
8. To minimize static electricity consider a hard surface floor covering or a
static dissipative mat. Make sure all static mats are grounded to the power
outlet. There are also some anti-static sprays that you can treat carpets,
chairs, upholstery and desk surfaces.
For the most part, these recommendations will not involve major expenses
in homes that already conform to practices permitted under the National
Electrical Code. They are especially inexpensive when you compare their
cost to the cost of losing your sensitive electronic equipment and all of the
data you've stored in it.
You can do something about power quality. Think about it the next time
your PC starts acting up.
If you have a Case History to share or would like to receive additional
information, contact: 
powerquality@cda.copper.org 
 
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