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CHAPTER
Power Protection
In this chapter, you will learn about
• Identifying power protection options
• Installing power protection options
• Alternative power sources
When the control of an entire home depends on the availability and reliability of electrical power, regardless of the control method or protocols in use, the inclusion of
certain power protection devices can help ensure that the system will remain powered
and operational at all times. It doesn’t do much good to have a home control system in
a home when there are electrical problems, interruptions, or failures.
This chapter looks at the device that can be included in a home control system
to make sure that the electrical power it needs provides both protection and
availability.
Planning for Electrical Protection
The good news is that a home control system is powered by electricity, something you
should be able to take for granted, provided the electricians do their jobs. However, the
bad news is that the home system is powered by electricity, and you need to protect the
system from that very same electrical power.
A home’s electrical power supply experiences random spikes, surges, and lulls almost every day and, in some cases, every hour. Exactly why these events happen isn’t
really the issue. The issue is that protection must be designed into the system to prevent
these events from damaging the system and its devices.
Electrical Events
External AC power sources can pass on a variety of power-related problems, including
the following:
●
Line noise Consists of small variations in the voltage of the power line. A
small amount of line noise is normal in just about every system and all but the
very low-end devices can handle it. An electrical device connected to its own
circuit (an unshared power line) should have little trouble with line noise.
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However, for a device that shares a circuit with a refrigerator or a megaton air
conditioner, line noise is not only a certainty, but it’s likely that the line noise
will cause problems. For example, if a transformer is connected to an AC power
source with high levels of line noise, it may eventually have its power-regulating
circuits burn out, after which time the line noise would pass through to the
devices connected to the transformer.
●
●
●
●
Power surge A power surge or spike, which is also called an over-voltage
event, occurs when electrical disturbances, such as distant lightning strikes or
other anomalies in the electrical supply grid, create a sharp rise in the voltage
level that is passed onto the power supply lines. In most situations, a spike or
surge lasts only a few thousandths of a second, but depending on the amount
of the rise in the line voltage, that is plenty of time for the voltage to increase to
double, triple, or spike even higher. High voltage spikes and surges, if frequent
enough, can degrade the electrical circuits of a home’s electrical devices. In
fact, multiple surges occurring frequently enough can eventually destroy some
electrical devices, such as a computer’s power supply.
Brownouts Called an under-voltage event, a brownout is the opposite of a
power surge (over-voltage event) and occurs when there is a sudden dip in the
power line voltage. In most cases, the power level drops below normal levels for
a time and then returns to normal. Brownouts are extremely common during
periods of heavy load on the electrical system, such as hot afternoons or cold
mornings. The reduced voltage level causes many devices to run slower than
normal or malfunction in other ways. Low voltage for an extended time can do
just as much damage as spikes. A brownout doesn’t typically last too long, but
it can.
Blackouts A blackout occurs when the power fails completely. The problems
caused by a blackout are usually more frustrating than damaging, but the
fluctuation of power surrounding a blackout can cause harm. Typically, any
damage associated with a blackout occurs when the power returns suddenly,
usually in the form of a huge spike.
Lightning strikes This is the big spike, and it can deliver a million volts or more.
I don’t need to tell you what would happen if one were to hit a home directly.
However, a strike even in the vicinity can result in a very high voltage spike.
NOTE Electrical events can cause two types of damage to an electrical
device: catastrophic damage, which means a device is destroyed all at once by
a single event, and degradation, which means a device is damaged slowly over
a period of instances and has intermittent problems before failing altogether.
Surge Suppression
The most common electrical system event is a power surge or spike, which is a temporary
increase in the voltage supplied on the electrical lines. For the most part, any power surge
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Figure 35-1
A surge
suppression plug
strip
Photo courtesy of American Power Conversion Corporation.
to a home is passed on through the electrical distribution panel to the circuits in the home.
The installation of surge suppression devices is the best and most economical way to prevent damage to any of the devices on the structured wiring system.
The least expensive and perhaps the least protective way to protect against electrical
surges is a power strip surge suppressor, like the one shown in Figure 35-1. Surge suppressors are generally available and the most commonly used protection device. The
device shown provides protection not only for electrical devices, but also provides surge
suppression to telephone and data network links.
The primary component of a surge suppressor is a metal oxide varistor (MOV),
which, in effect, takes the hit from voltage spikes. However, an MOV can be defeated by
one big spike or an accumulation of small surges over time, which is why some surge
suppressors have an LED to indicate that the MOV is still intact. A surge suppressor absorbs spikes and surges and smoothes out line noise, which is called line conditioning.
The rule of thumb for selecting a surge suppressor is that you get what you pay for.
The two main features for choosing a surge suppressor are
●
●
Clamping voltage
circuit.
The voltage at which the suppressor begins to protect the
Clamping speed The amount of time that elapses between detection and
protection.
Here are some other characteristics to consider when selecting a surge suppressor for
a home system:
●
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Energy absorption Surge suppressors are rated in joules, which is a measure
of their capability to absorb energy. The higher the joules rating, the better
the protection. Basic protection is 200 joules; 400 joules represents good
protection; and 600 joules is better protection.
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●
●
Line conditioning The line conditioning capability of a surge suppressor is
measured in decibels. The more decibels of noise reduction, the better the line
conditioning.
Protection level Surge suppressors have three levels of protection indicated
as the maximum number of watts a suppressor allows to pass through. The
standard ratings are (better to good) 330, 400, and 500.
NOTE Underwriters Laboratories (UL) standard 1449 covers the
construction and performance of surge suppressors. A suppressor with
a UL approval has met this standard and will provide protection to its
rated capacities.
A variety of surge protectors and suppressors are available for virtually all parts of
a home automation network, including units designed specifically for wiring carrying
electrical signals, including audio/video and network components (see Figure 35-2).
Power Conditioning
A power conditioner is an electrical device that is designed to remove electrical noise
and crosstalk from an electrical line. Power conditioners come in all sizes, but common units for use with a single system or subsystem, such as a home theater, can have
from 1 to 12 or more receptacles and outlets, each of which is isolated from the others.
Many home system power conditioners, like the one shown in Figure 35-3, condition
not only the electrical power, but also the electrical impulse transmissions for video
and audio.
In some situations, depending on the design of the wiring and the systems attached,
it may be a better choice to install a whole home power conditioner (see Figure 35-4).
Models of whole home power conditioners are available in a variety of power load ratings and abilities.
Figure 35-2
A data network
cable surge
suppressor
Photo courtesy of Tripp Lite.
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Figure 35-3
A power
conditioner
designed for
home theater
systems
Photo courtesy of Belkin International, Inc.
Figure 35-4
A whole home
surge suppressor
and power
conditioner
Photo courtesy of New Frontier Electronics, Inc.
Inverters
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In some rare instances, it may be necessary to invert direct current (DC) to alternating
current (AC) power for a particular device. This requirement most likely occurs when
a home AC device is to be used in a DC-powered environment, such as a car or a recreational vehicle. It is possible that a homeowner may wish to use a device purchased
specifically for a DC-powered environment in their home. Power inverters convert DC
power into 120 V AC power. Figure 35-5 shows a power inverter.
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Figure 35-5
Front and rear
views of a power
inverter, which is
used to convert
DC power into
an AC current
Photo courtesy of Tripp Lite.
Applying Protection to Cable
While the protection method used to protect the different cabling types used in a home
system is essentially the same, each cable has one or two unique characteristics. The
following sections describe the unique protection methods used for each cable type.
Protecting Telephone Lines
In the event of an electrical storm or lightning strike, power can surge up the telephone
lines just as fast as it can on power lines. Surge protectors should also be installed to
protect any distributed phone lines between the network interface device (NID) and
the distribution panel. In addition, add surge protection to any door intercoms before
they connect to the house phone system, as they are located outside and susceptible to
lightning hits.
Protecting Coaxial Cable
Surge suppression should also be added to coaxial cable lines that connect exterior
sources to interior systems, such as the lines that provide cable television, an exterior
antenna, or the lines connecting a digital satellite receiver to its dish outside the home.
The best devices for this purpose include a silicon avalanche diode (SAD) as their
primary level of protection from over-voltage surges that may enter and be carried on a
coaxial cable into a home. SAD devices provide fast and nondegrading surge protection
for coaxial data and video source lines.
Protecting Twisted-Pair (Network) Cable
Like telephone lines, unshielded twisted-pair (UTP) cable, and more importantly, the
devices it interconnects, should be protected from line noise and especially electrical
surge. Devices like the one shown earlier in Figure 35-2 should be installed at each network termination and grounded to grounding lugs on the terminating device.
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Alternative Power Sources
An uninterruptible power supply (UPS) provides a constant (uninterrupted) power
stream to the electrical devices connected to it. Under normal operating conditions,
most surge suppressors can handle short brownout conditions. However, when the
AC voltage drops below a certain level or is disrupted completely, a UPS is designed to
provide power for a certain amount of time.
All UPS units have two sets of circuits. One side is an AC circuit that provides
surge suppression. The other side is a battery and a DC to AC converter. The batteries inside a UPS store a DC charge that must be converted to AC when needed to
replace lost voltage.
There are two types of UPS units available, which differ in the following ways:
●
●
Standby Operates normally from its AC side. When the power drops, it
switches over to its battery backup side.
In-line UPS Operates normally from its DC or battery backup side. The AC
side is used only to maintain the power stored in the batteries or in the event of
a problem with the battery-powered circuits.
NOTE UPS units are often confused with a standby power supply (SPS),
or battery backup, which supplies power only when none is available and has
no power-conditioning capabilities.
The use of a UPS unit with home automation systems is optional, but in the case
of electrically powered telephones and security systems, having power for even a short
period of time after a power failure may be a necessity in some home situations.
Chapter Review
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There are some basic electrical issues that need to be addressed during the planning
phase for a structured wiring project, especially electrical event protection.
External AC power sources can pass on a variety of power-related problems, including line noise, power surges, brownouts, blackouts, and lightning strikes. Surge suppressors are generally available and the most commonly used protection device. Surge
protectors should also be installed to protect any distributed phone lines between the
NID and the distribution panel and any coaxial cable lines such as cable service, antenna or satellite. An uninterruptible power supply (UPS) provides a constant (uninterrupted) power stream to the electrical devices connected to it.
Power conditioning can serve to insulate a home from electrical events, but at the
least surge suppression should be used to minimize any potential damage from electrical surges, spikes, and brownouts.
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Questions
1. What is perhaps the single largest external danger to an electrical system?
A. ESD
B. Improper grounding
C. Electrical events
D. Number of electrical outlets in home
2. Which of the following is a low voltage electrical event against which power
protection should be installed in a home system?
A. ESD
B. Surge
C. Electrical noise
D. Brownouts
3. What electrical event consists of small variations in the voltage of a power line?
A. Brownout
B. Blackout
C. Line noise
D. Power surge
4. What electrical event is also known as an over-voltage event?
A. Brownout
B. Blackout
C. Line noise
D. Power surge
5. What electrical event can cause devices to run slower than normal or malfunction?
A. Brownout
B. Blackout
C. Line noise
D. Power surge
6. What electrical event occurs when the power fails completely?
A. Brownout
B. Blackout
C. Line noise
D. Power surge
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7. Which two of the following are the types of damage that can occur as the result
of an electrical event?
A. Asynchronous
B. Catastrophic
C. Degradation
D. Synchronous
8. What device should be installed to protect against power spikes?
A. Power conditioner
B. Inverter
C. Surge suppressor
D. Uninterruptible power supply
9. What unit is used to measure the energy absorption capability of a surge
suppressor?
A. Amps
B. Ohms
C. Joules
D. Volts
10. An electrical current inverter is most commonly used to convert ______ current
to ______ current.
A. Out of phase; in-phase
B. 220; 110
C. AC; DC
D. DC; AC
Answers
1. D. The number of outlets in a home has no bearing on the design and planning
of a structured wiring system, beyond their use as a guideline to the placement
of structured wiring outlet boxes.
2. D. A brownout is a low-voltage current that can damage electrical systems
over time. In many ways, it can be more damaging to power supplies than
intermittent surges or spikes.
4. D. A power surge raises the voltage of the electricity on the line for short periods
of time.
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3. C. Line noise or electrical noise on an electrical line can raise and lower its
voltage, causing damage to connected devices over time as well as disrupting
any communications signals transmitted over the electrical system.
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5. A. A brownout occurs when the line voltage is reduced for relatively extended
periods of time.
6. B. A blackout is essentially what it sounds like. The damage from a blackout
typically occurs from a surge when the power comes back on.
7. B and C. Some electrical events can destroy equipment and others cause small
amounts of damage that can cause intermittent failures before the equipment
is destroyed.
8. C. A surge suppressor can help to mitigate power surges and spikes. However,
a surge suppressor should be checked after an electrical event to insure it is still
effective.
9. C. Joules measure the capacity of a device to absorb electrical voltage.
10. D. Inverters are most commonly used to allow AC devices to be powered on
a DC line.
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