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8/4/2019 Application Guide for Surges
1/15Bowthorpe Low Voltage Division Tel: +44(0) 1273 692 591 Fax: +44 (0) 1273 676 637 e-mail: lvsales@bowthorpe-emp.com
A Guide to
Lightning andSurge Protection
A Guide to
Lightning andSurge Protection
to BS6651: 1999 Annex C
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Contents
What are surges, transients and spikes? 3
Who should read this guide?
Who are Bowthorpe? 3
What can Bowthorpe offer you?
Surges 4
What is a surge? Where do surges come from? Surges, transients, spikes - whose problem are they?
Lightning6
Direct Coupling Earth Voltage Inductive Coupling
Risk Assessment within BS6651 7
What the insurers say! 8
Commercial considerations
BS6651: 1999 Annex C - Co-ordinated Protection9
The Co-ordinated Protection Strategy 10
Its cheaper than you think How do surge protectors work? Design considerations
Product Selection Guide 11-14
AC Power Systems Network and Telecom Systems
Product selection diagram
Telecommunication and wireless protection systems
Questions and Answers 15
Common Misconceptions 15
Page
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odays business environment is a
world dominated by computers.
Every aspect of our working lives
depends on the efficient functioning of
critical IT systems.
For many companies, disruption of the IT
system impacts heavily on the day to day
health of the organisation. Should
damage occur, the cost can be severe, in
some cases, catastrophically so.
Clearly, the responsibility to prevent such
a disaster occurring can lie with several
people within the company. In some
cases, external bodies such as the
companys insurer may be the driving
force to implement an effective protectionstrategy.
The objective of this guide is to
familiarise you with the basics of surge
protection, allowing you to effectively
counter the threat posed by lightning and
surges to the life of your business.
owthorpe is an internationally
recognised, ISO9001 registered,
specialist manufacturer of surge
protectors for Mains Power, Voice and
Data Systems. We have representatives
on various international committees
including the IEC SC37A sub committee,
which is responsible for developing the
worlds first truly international surge
protection standard, IEC 61643
This application guide is designed for
consultantsdesignersspecifierscontractorsend usersusers of electronic systemsinsurersIT managersfinance directorsfacilities managers
telecom managerstechnical and non-technical
people.
It will enable you to select the
appropriate surge suppression
equipment to fit any particular
application and will provide an insight
into the phenomena of surges, what
causes them and how to stop them.
Technical hotlineSite surveysConsultancy advice
Comprehensive product rangeState of the art technologyCompetitive pricesSpecification of individual
products and complete protection
systems
Factory and laboratory visits,witness tests
Professional CPD accreditedpresentations
Training seminars
Who should read
this guide?
What are surges, transients and spikes?
Who are Bowthorpe?
What can Bowthorpe
offer you?
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surge, also referred to as a spike,
glitch or transient overvoltage, is
a very short timescale deviation
from the normal operating voltage of an
electrical system.
Typically lasting tens of micro-seconds,
surges can reach values of several
thousands of volts, thus making them
Voltage
Surges
20msTime
Voltage
50s
8/20s surge (enlarged in time)
Time0 0
Small surges can cause... Spurious crashing of computer
equipment
Corruption of data transfer over
networks
Unexpected printer output
Gradual component degradation leading
to equipment breakdown
Internally generated surges occur on a
daily basis and can be easily
suppressed utilising surge protectors in
the form of plug adaptors, socket strips
or in-line units.
In some cases, Radio Frequency
Interference (RFI) filtering is incorporated
within these protectors. RFI, or noise, is
rarely damaging to equipment but can be
an annoyance if experienced regularly.
Far more damaging to equipment and
systems are the large spikes typically
generated externally to the building and
normally associated with lightning activity,
Surges
What is a surge?
Where do surges come from?
ost surges are caused by an
electrical load either within or
outside a building being switched
on or off. Particular causes of transients
include large machines, lift motors,
welding machines and large printers.
Fortunately, most internally generated
transients tend to be reasonably small
(typically only a few hundreds of volts)
and consequently their effects range from
the short-term: data corruption, system
crashes and lock-up, to the long-term:
insiduous component degradation which
is a major factor in system reliability
assessments.
particularly damaging for computer
related equipment.
Most surges occur on the mains supply,
but they also pose a real threat to any
system utilising copper communication
cables, such as a Local Area Network
(LAN) or telephone systems.
Where do surges
come from?
Inside the Building
Factory equipment Office equipment
Air conditioning and lift motors
4
What is a surge? A surge is a short transient deviation of line voltage from the nominaloperating level.
Most surges occur on
the mains supply but
they also pose a real
threat to any systemutilising copper
communication cables
Far more damaging
to equipment and
systems are the
large spikes
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Large spikes can
lead to...
Failure of computer power circuits
Failure of communication interfaces
Irreversible damage to hardware
electricity supply faults or switching of
large loads within the power distribution
network (National Grid/ Regional
Electricity Companys [RECs]).
Large transients, such as those caused
when there is a nearby lightning strike,
can reach values of 6000 Volts and
Since all types of transient disturbances
can be transported via electrical wiring,
nearly all electronic equipment, from
telephones and fax machines to large and
expensive computer systems, are at risk.
The extent of damage sustained ranges
from corrupted data communication toimmediate physical destruction of hard-
ware and, in some cases fire risk or even
5
Where do surgescome from?
The Outside World
Lightning
Transformer tap switching, power
station, sub-station and distribution faults
Power cross faults
Low quality generators
3,000 Amps inside a building.
Surges of this magnitude can cause
extensive damage to computer circuitry,
literally blowing up sensitive components
such as micro-chips and in some cases,
causing fire within computer or
communication equipment.
compromised human safety.
You may even have already suffered
equipment failure through surge damage
without even knowing it! The cause of a
computer breakdown often passes
unknown with the computer being simply
replaced or repaired. Component fatiguedue to repeated transient attack goes
unnoticed until its too late.
Everyones (including yours!)
Surges, Transients, Spikes - whose problem are they?
Bowthorpe supply a wide range of surge protection products to suit all needs
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assessment which establishes the
prominence of the building given its
geographical location.
The purpose of a structural protection
system is to prevent damage to the fabric
of the building, prevent risk of fire and
safeguard personnel from the dangers of
inadvertent electrical shocks.
From the perspective of structural
protection for the building, a lightning
strike to the surrounding area is of no
consequence. However, from the point of
view of surge protection of equipment
within the building, nearby lightning
strikes are as important as direct strikes.
The reason for this is that a structural
protection system is dealing with the
primary effects of the lightning strike,
whereas surge protection is dealing with
the secondary effects of lightning.
The following diagrams portray three
important mechanisms by which lightning
strikes can affect sensitive equipment.
y far the most prominent cause of
damaging transients is nearby or
even direct lightning strikes.
Lightning discharge currents can be as
high as 200,000 Amps in the UK, with
the average discharge current being
28,000 Amps.
Obviously, such massive currents would
vaporise any electronic equipment or
cabling in the case of a direct strike to a
cable.
Fortunately, this situation is rare as most
equipment and cabling is located within a
building. Lightning will always tend to
strike the most prominent feature, which
is invariably the roof of the building!
The British Standard for Lightning
Protection : BS6651:1999 goes into great
detail on the whys and wherefores of
designing and installing a structural
protection system (lightning conductors)for the building. The decision as to
whether to install a structural protection
system is essentially based on a risk
6
Lightning
Direct Coupling
Direct Coupling
The bulk of the discharge current from a
direct strike to a power conductor pylon,
for example, will be conducted to earth.
Some proportion of the discharge current,
however, will be conducted as a surge on
the cable. The magnitude of the surge
current varies due to the length and type
of the cable as well as the magnitude of
the lightning strike.
Sensitive equipment can therefore be
damaged even when the lightning strike
is some distance away.
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7
Inductive Coupling
Earth Voltage
Earth Voltage
Inductive Coupling
200
2000
400
400
600
600
800
1000
1200
NationalGridNorthing(km)
National Grid Easting (km)
During a cloud to ground lightning strike,
the strike point is raised to a very high
voltage owing to the large current (up to
200kA) being conducted through the
ground (which has a finite resistance).
Typically this value could be in the
hundreds of thousands of volts for a
fraction of a second. The further away
from the strike point, the lower the
voltage value. Depending on local soil
conditions and climate, this voltage
disturbance can be significant up to about
2km away.
As a consequence of this earth voltage
disturbance, any building within 2km of a
lightning strike will experience a
fluctuation of its mains earth voltage.
Because the equipment within the
building may be connected to other
electrical systems, such as equipment in
another building, the electricity sub-
station etc., there exists a situation where
A current carrying cable, by virtue of its
electromagnetic field, will induce a
current flow in any nearby cable running
parallel to it.
the power and data cables entering the
building may experience different earth
voltages at each end. This causes a
current to flow in the connected electrical
wiring which is perceived by the
equipment as an incoming surge.
Risk Assessment within BS6651
ifferent areas of the country and
the world experience higher
levels of lightning activity than
others, and the climate largely
determines the overall trend. Many of the
variable factors are built into the risk
assessment procedures in BS6651.
The risk assessment for structural
protection is essentially determining how
prominent the structure is and therefore
how attractive it is to a lightning strike.
The risk assessment for surge protection
is more complex. As well as determining
how vulnerable the building is to a direct
strike, the risk assessment takes into
account the quantity of external cables
entering the building and the nature of the
equipment within the building as this
determines the Consequential Loss factor
should a system be affected.
Although the risk assessment procedurecan be a little complicated, with care it can
be a powerful tool to establish a realistic
appraisal of the risk to a system.
This basic electrical phenomenon is
responsible for the third mechanism of
lightning associated surges. A cloud to
cloud lightning strike, of which there are
approximately up to 1 million a year in
the UK, sets up a massive
electromagnetic field. Any cable which
lies within this field is subject to the
electromagnetic forces of it. Induced
currents are created, especially prevalent
where there is a large network of cables
above ground. Lightning strikes to nearby
pylons, trees etc produce similar results.
Map showing thunderstorm days per year throughout the world
90
80
70
60
50
40
30
20
10
0
10
20
30
40
50
60
70180 150 120 90 60 30 0 30 60 90 120 150 180
4060
40
40
60
80
60
60
80
30
5
5
5
20 20
10
1040 140
140
100
100
80
402010
20
60 60
5
10
100 120
40
60
4020
10
5
1
20
10
10 140
140
140
120
80
80
180180
100
60
60
10
40
5
5
1
30 20
10
1
140
5
3040
20
605
20
100 20
40
8040
80
5
10
1
405
520100 10
Number of lightning flashes to the groundper km2 per year for the uk
Extracts from BS6651 are reproduced with the permission of BSI. Complete editions of the standards can be obtained by post fromBSI Customer Services, 389 Chiswick High Road, London W4 4AL.
NOTE: This map is based on information from the World Meteorological Organisation records for 1955.
0.1 0.4
0.2 0.5
0.3 0.6
The lightning density map was compiled byElectricity Association Technology Limitedfrom data accumulated over four years fromits Lightning Location System.
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What the Insurers Say!
Commercial Considerationsowadays, with the ever increasing
amount of information technology
being used for businesses, the
costs of equipment repair and replacement
have become a major concern for theinsurance companies.
In some cases, they have provided the
finances to replace computer systems
worth some 100,000s that have been
destroyed by lightning or other surge
phenomena. Downtime and other
consequential losses often cost far more
to replace. Many other cases occur in
domestic and small business applications
where equipment worth 100s or 1,000s
has been damaged.
The insurance companies now recognise
surge protection as being a solution to
this problem. They know that a total
protection system can be fitted for
a fraction of the equipment
replacement value.
8
Latest statistics on claims
for hardware and
consequential loss have
astonished insurers to such
a degree that they have had
to reassess premiums for
any company heavily reliant
on information technology.
An organisation that has taken BS6651
very much to heart is the Loss Prevention
Council, or LPC. The LPC is funded by
the Association of British Insurers and
Lloyds of London and is involved in all
aspects of loss prevention and risk
control on a world-wide basis. It is,
therefore, the body that the insurers refer
to for guidelines when drawing up their
insurance policies and assessing
potential relatively new risks.
BS6651: 1999 Annex C has been taken
very seriously by the LPC and, in turn,
the insurance companies, particularly inlight of recent avoidable claims for
computer hardware damage and
consequential loss as a result of surges,
spikes and transients.
LPC statistics on claims for hardware and
consequential loss have astonished
insurers to such a degree that they have
had to reassess premiums for any
company heavily reliant on information
technology. A single such claim for over
0.5 million to one insurer has certainlyfocused the insurance industrys
attention to this subject. It is now
becoming the insurers policy to
either demand higher premiums or
even refuse cover if the
recommendations of BS6651 are
not acted upon!
The statistics reveal that 60-70%
of commercial claims could be
directly attributed to computer
hardware failure andconsequential loss due to
surge disruption or damage.
Clearly, no organisation
appreciates higher insurance
premiums, but, equally, no
successful company can
accept computer failure
resulting in poor customer
service.
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he British Standard BS6651:
1999 is titled Code of Practice
for Protection of Structures
Against Lightning and outlines the
general principles of applying lightningprotection to buildings and structures.
It was in 1992 that Appendix C
(changed to Annex C in the 1999
revision) was originally incorporated
within BS6651 and provided general
advice on protection of electronic
equipment within or on structures against
lightning. BS6651: 1999 Annex C
gives details on the following aspects
of surge protection:
How to assess the lightning exposurerisk to equipment
Routes along which surges can entera building and where they go within
the building
Deciding factors for installing protection Recommended levels of protection in
a co-ordinated protection system
AC Power Protection
For AC power, Annex C defines three
different categories of surge protection
that vary in surge handling ability,
each designed for installation at
particular locations within a building
supply network.
Category C - The supply side of theincoming distribution board
Category B - The mainsdistribution system
Category A - The load side ofsocket outlets
Although not confirmed in BS6651, these
three categories reflect with the location
categories used in the American standard
IEEE C62.41 (1991).
Each BS6651 location category is divided
into three groups which suit different
exposure or lightning risk levels. These
are known as the low, medium and high
system exposure levels.
Bowthorpe products are suitable for the
high system exposure level of each
category and also address the lower
exposure levels. By designing our
products in this way, we greatly simplify
product selection.
The surge ratings for each location
category are the peak surge voltage and
peak surge current that will normally
occur at that location in the supply network.
Any protection device designed for
these categories must be able to
withstand the respective peak surge
current and voltage. The following
table indicates the protection levels
required for the high system exposure
group of each category.
Network & Telecom
System Protection
Annex C also defines a location
category C for communication
systems which specifies a 10kA
protection level. However, communication
cable exhibits a higher electrical
impedance that helps to dissipate the
surge energy.
In communication systems, therefore, as
long as category C protection is fitted, it
is not normally necessary to protect
against incoming surges at location
categories B and A.
BS6651: 1999 Annex C. - Co-ordinated Protection
9
Location category C B A
Peak surge voltage 20kV 6kV 6kV
Peak surge current 10kA 3kA 500 A
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By carefully selecting which parts
of the computer system are mostcritical to your business operations,
implementing total protection need
not be very costly and will easily be
within the reach of small and large
businesses alike.
A risk assessment should be performed
to identify key equipment and to
weigh the costs of protecting this
equipment against the potential losses
to the business in system downtime,
maintenance and reduced performance.
The Co-ordinated Protection Strategy
Its cheaper than you think How do Surge Protectors
work?
Different kinds of protector use differenttypes of components or combinations
thereof to suppress surges, transients
and spikes.
As described earlier in this guide, a surge
is a rapid fluctuation in voltage occurring
on a signal or AC power cable which, in
many cases, will contain enough energy to
cause disruption to communications and
often physical damage to electronic circuitry.
The suppressor components used are
normally one of three basic technologies:
gas discharge tubemetal oxide varistorsolid-state semi-conductor.
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To be effective, surge protection must
survive the maximum transient
overvoltages and resultant currents that
occur at the different locations and only
pass the residual part of the surge that
will not cause damage.
It is therefore necessary to know the
equipment transient design level
(ETDL) for the equipment to be
protected. This is the maximum surge
voltage level that will not impair the
performance of the equipment and is also
known as the immunity level. The
residual part of a surge which passes
through the protector is known as the
let-through voltage or transient control
level (TCL).
For protection to be effective, the TCL
must be less than the ETDL and include
a reasonable safety margin Vm:
TCL+Vm
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12
Plug-in mains protection products
MDSP DIN rail mount replaceable modules
Network Barrier & Telecom TLP Series
Network and Telecom
Systems
6651C Protector Step 1: Location Category C
Locate all communication cables
entering the building including PSTN
dial-up voice lines and leased lines,
ISDN and network lines. All incoming
cables that carry signals on wire
conductors must be fitted with
appropriate category C protection from
Bowthorpes extensive range of
datacom, telecom and network barriers.
Step 2: Location Category B
Identify sub-distribution panels that
supply mission-critical hardware such as
mini-computers, PABX systems,network file-servers and mainframes.
Install the location category B protection
described below.
With the increasing use of distributed
networks, many users prefer to protect
all sub-distribution panels with these
economically priced products.
Step 3: Location Category A
Fileservers, mainframe computers,
PABX, and other such hardware are
important for providing critical services
to the company and should, therefore,
be fitted with category A protection.
Our range of plug-in devices and
socket strips provide fine-tuned,
backup protection for the most
important equipment and will suppress
surges and interference from inside
the building.
Category C Products
Network Barrier & Telecom
TLP Series
10kA rated barriers are available in DIN rail
mounted format for datalines. For telephone
PABX systems, Krone mounted units are
available in 10-line and single-line variants.
Category A Products
Protector Plugs and
Adaptors
This range of single-outlet surge
suppressors and hardwired plugs are
available with surge only protection and
various ratings of RFI filtering. UK,
French and German formats are offeredand all units feature thermal protection
against surges exceeding their rating,
unlike most low cost products.
Socket Strips
These AC mains socket strips are
available in UK, French and German
formats with options for surge protection,
RFI filtering and a choice of from four to
ten socket outlets. All strips feature
thermal protection.
Category B Products
6651C ProtectorA compact, hard-wired, panel mounting
protector for sub-distribution panels
available in single and three phase models.
Spur Protector
Ideal for the protection of equipment on
individual ring mains, this unit can be
either wired to equipment as an inline
protector or can be hardwired into wall
mounted conduits.
DSP1 and DSP3
General purpose, hard-wired, single and
three-phase distribution panel protectors
with 30kA of surge capacity. Optional
relay contacts provide remote indication
of protection status.
indication of protection status. Models
with Silicon Avalanche Diode Modules
(SAD) with extremely low clamping and
exceptionally fast response times are
particularly suited to mobile telecom
applications.
DSP1 and DSP3
Spur Protector
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15
TRANSFORMER BACKUPGENERATOR
11KV POWER(3-PHASE)
UNDERGROUNDCONDUITS
P.A.B.X. AND OTHERCOMMUNICATIONS
EQUIPMENT
SURGES ARE GENERATED INSIDEBUILDINGS BYAIR CONDITIONERS,
LIFTS, PHOTOCOPIERS, DRINKSMACHINES, FACTORY MACHINERY,
REFRIGERATORS ETC.
SURGES ARE GENERATEDOUTSIDE BUILDINGS BYLIGHTNING,
POWER FAULTS, SWITCHING ANDCONTACT BETWEEN POWER AND
COMMUNICATIONS LINES, ETC.
WALLCONDUIT FOR MAINSAND DATALINE CABLING
415V POWER(3-PHASE)
Supply
Distribution
Surge
Protector
Sub-distribution
Panel Protector
DIN-rail mountab
dataline sur
protecti
Telecom surge
protection
Surge
Protected
Socket Strips
Service Entry
Surge Protector
41
2
9
1
9
8
7
6
6
4
7
12
Spur and InlineSurge Protector
9
67
8
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Telecommunications and Wireless Protection Systems
14
Aircraftwarning light
Microwave dish
TV antenna
Transmissionequipment Digital switching
equipment
Mains powersupply
Typical steelcabin/equipment
room
Induced surgeinto buriedtelecom cable
Common earthbar connected to
all electronicequipment andbonded to theearth ring
DC power equipment(batteries, rectifiers,inverters, converters)
FM broadcast ormobile telephone
antenna
Tower footingring earth
Equipotentialearth bonding
3
4
1
2
1MDSP AC powerprotection 4
Co-axial surge protector
barriers
FEATURES:
Exceptionally high surge handling Two stage (redundant) protection Replaceable DIN rail mount modules Dual thermal/current overload fusing Status indicators with remote signalling Silicon Avalanche Diode models
available for extremely low clampingand exceptionally fast response time
Site wiring fault indicator
APPLICATIONS: Front end of building protection for
mission critical sites and applications SAD models particularly suited to
mobile telecom applications.
FEATURES:
Din rail or panel mounting Low let-through voltages
Fast response times High surge handling capability
Negligible effect on normal lineoperation
APPLICATIONS:
LANs EPOS
CCTV Ethernet Plant & Process Control
Signalling and telemetry
Modular Distribution
Surge Protector
3
Telecommunications lineprotector installed inMDF to protect sensitivetelecoms equipment
FEATURES:
Surges reduced to below normal signalvoltage
High surge handling capability
Negligible effect on normal lineoperation
Models available for connection toLSA-Plus termination strips
Optimum performance with lightningrelated surges
APPLICATIONS: PABX PSTN
Telephone and facsimile Computer communications using
voice line modems
Telecom Line
Protectors
2Surge protector installedon AC power supply toaircraft warning light
FEATURES:
High surge handling capability Two stage (redundant) protection Full protection status indicators
Remote signalling version available Fast response time and low let-
through voltage
APPLICATIONS:
Front end of building protection
Sub distribution panel protection
Individual protection of critical &costly equipment such as computer
systems
Distribution Surge
Protectors
Network & Signal Line
Barrier Protectors
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I dont need surge protection because my
building already has structural protection.
WRONG!
Structural lightning protection and lightningconductors do not protect the sensitive
equipment within the building.
I dont need surge protection because my
system is connected to a UPS.
WRONG!
Most UPSs are not designed with BS6651 in mindand consequently any surge protection fitted is
likely to be limited in its surge handling capability.
Any protection fitted inside the UPS is specificallydesigned to protect its own electronics, not the
equipment connected to it.
UPS bypass switches, when in operation, reduceany protection afforded by the UPS.
Lightning never strikes twice.
WRONG!A site that has been struck once is clearly
susceptible and will often suffer problems on a
regular basis.
My site is surrounded by tall buildings,
so is safe from lightning damage.
WRONG!
Tall buildings may attract lightning away fromyour site, but, your systems will be at risk from
the secondary effects caused by the
electromagnetic pulse generated when lightning
strikes nearby.
Your site is also at risk from surges andtransients present on incoming power andcommunication cabling.
The cabling between my two buildings is
underground, so doesnt need protection.
WRONG!
When lightning strikes the ground, even 1 or 2km away, the current discharged raises the
ground potential in the surrounding area by
100,000s of volts depending on proximity to the
strike. While the current dissipates through theground, a difference between the building earth
points stresses the cable and any connected
equipment.
QI didnt hear anything aboutsurges and transients tenyears ago. Why are they causing
problems NOW?
ATodays computers use smaller and
more sophisticated electronic
components than ever before which are far
more sensitive to transient voltages than
earlier technologies.
Furthermore, we can now put computers
and communication equipment anywhere
we want so must be aware of variations in
the quality of different operating
environments. Perhaps more importantly,
the electricity supply companies are not
required to provide computer-grade power,
so it is our responsibility to ensure thepower used for our computers is clean.
QWe get very little lightning inmy area. Do we still needtransient suppression equipment?
ALightning is only one source of
transients. Repetitive, low level
spikes on power and communication lines
cause circuit degradation and eventual
example, different types of computer network
use a variety of connector formats, signal
levels and operating frequencies. Some
applications are contained within one
building, however, others include data and
power connections between several buildings
which have different protection needs.
QHow do surge protectorswork?A
Surge protectors continuously
monitor the power or signal line for
overvoltages. When the voltage rises
above a certain level components inside
the protector divert the excess energy to
earth and limit the voltage to a safe level.
QWhat is thermal overloadprotection and why do I
need it?
ABowthorpe products have thermal
overload protection fitted as
standard. Surge protection products where
protection elements are not fitted with this
safety feature can overheat under fault
conditions and give rise to the risk of
electric shock or fire.
failure. These spikes are frequently caused
by utility power switching and heavy
industrial power users.
QIs it possible for transients to
affect my equipmentunnoticed?
AAbsolutely. Small transients can be
an invisible problem, they dont
necessarily cause immediate equipment
failure, but WILL cause micro bullet holes
inside semi-conductor electronics leading to
degradation.
After some period of time, the hardware will
fail and be replaced under the assumption
that it died a natural death of age.
However, its life expectancy is actually
shortened by the degrading process. In
other words, the useful life of computer
equipment can be extended by installing
surge protection.
QIs there one completesolution that provides totalprotection?
AEvery system and application is
different in one way or another. For
Questions and Answers
Common Misconceptions