Understanding Surge Suppression Specifications and Terminology
Those who have a need to specify or purchase quality VXUJHSURWHFWLYHGHYLFH63' equipment
find it difficult to compare devices and select the best 63' for their application. Decisionmaking
information is contained in magazine articles, advertising material, personal advice, and
manufacturers’ specification sheets.
These information sources present specific terms and
performance test data under vague and ambiguous test conditions. This information must be properly
interpreted to provide a comparative, objective evaluation of 63'V. For most people, this is a
difficult task due to a lack of familiarity with the terminology and the fact that the data is often
intentionally provided in a confusing, complicated, or just plain misleading manner.
Some of the most commonly used terms on surge suppression specification sheets along with a
common definition of the term are provided below. An explanation of the importance of the data
normally provided on 63' specification sheets and how to interpret that data is also presented. The
first three terms allow an analyst to get in the right “ballpark” before a detailed comparison of 63'V
begins. The remaining 63' specification items allow an analyst to refine the requirements
for a specific application.
The Application
The first determination that should be made is the suitability of a 63' for the application under
consideration. Most manufacturers will provide guidance for the intended use of their products. This
is stated in common terms such as "For use on Service Entrances, Distribution Panels, Sub-distribution
Panels, and individual equipment locations with ampacities up to 800A." This means that this device
is designed for use on electrical breaker panels or individual pieces of electrical equipment that draw
less than 800 amperes of current. If your application is for a breaker panel with a rating above 800
amperes, you should check with the manufacturer. This is not a device that is to be plugged into a
common electrical wall receptacle. It is important to match your requirement with the design
application of the device. If you want to protect a data line, look for a data-line device. If you need
telephone line protection, look for a telephone device.
Power Input Frequency
This is the frequency of the system that is being protected. The standard power-frequency in the
United States is primarily 60 Hertz (Hz) or 60 cycles per second. In some areas of the United States
and outside of the United States it is 50 Hz. And, for some military applications it may be 400 Hz.
The 63' power input frequency should match the intended use.
Maximum Continuous Operating Voltage (MCOV)
This is the maximum electrical voltage allowable for the device. This data is provided as the
maximum allowable continuous root mean square (rms) voltage at the specified frequency. The
maximum voltage should not be exceeded. The 63' manufacturer should indicate which devices are
intended for each type of distribution circuit application.
63' Response Time
63' response time is the time it takes a surge-protective device to react to a transient voltage.
The response time or “clamping time” or “clamping speed” of an installed 63' differs significantly
from response time of its components. The response time of an installed 63' is a function of a
© Copyright 2010 Surge Suppression Incorporated® www.surgesuppression.com
55
number of variables, including:
● The basic 63' design; especially, the effectiveness of its high-frequency design.
● The switching speed of the components used in the 63' design. Solid-state components have an
intrinsic switching speed roughly of 500 picoseconds when measured without the component leads in
a proper test fixture.
● The transient amplitude, wave shape and rise time.
● The 63' installed lead length, or; the length of wire required to connect the 63' to the electrical
system.
Solid-state surge protection components can clamp a 1MV/µs (1 X 106 V/s) pulse in 500
picoseconds on the leading edge and follow it on trailing edges of the pulse. Thus, these solid-state
devices, from the standpoint of the transients, set and reset sufficiently rapidly to follow the leading
and trailing edge of these fast impulses. It is important to note that these measurements were made in
special microwave test fixtures with zero component lead lengths.
Clearly, solid-state components are considerably faster that gas tube surge arrestors. The solidstate devices in a computer operate in the gigahertz range. Gas discharge tube arrestors are not
capable of these high speeds.
As a practical matter, the circuit inductance of component leads and surge-protective device leads
completely swamp the rapid component response. This is documented in the IEEE C62.35-1987
Standard, “Junction Semiconductor Surge-Protective Devices Standard.,” This standard shows the
effect of lead length on the measured let-through voltage for a SAD. As the SAD component lead
lengths are increased from zero inches to a more practical length of 1.5 inches, the let-through voltage
increases from 210 volts to 1,200 volts. Thus, when SAD let-through voltage is measured with usable
lead lengths, the response time is dominated by the component lead length.
Expect a reaction time in the nanosecond range for a physically small 63' that is installed with
short lead lengths. The faster a 63' responds, the less time your equipment is exposed to the effects
of a surge or over-voltage transient. Response time data stated as "instantaneous" or "immediate" may
have been obtained using a zero lead length test. This prevents comparison with numerical data. Lead
length makes a huge difference.
Beware response time claims of “one picosecond” or “theoretical response time” of one
picosecond.
The maximum velocity in the universe is the velocity of light in a vacuum or
300,000,000 meters per second. In order for a device to respond in one picosecond at this maximum
possible velocity, its circuit path length into and out of the device in inches would be:
Circuit path length = (3 X 108 m/s)(1 X 10-12 s)(39.37 in/m) = 0.0118 inches.
For a 63' to have a one picosecond response time and to be capable of propagating energy into
and out of itself in one picosecond, the 63' would have to be roughly one-half the length of a one
celled microscopic amoeba. One 63' manufacturer claims a response time of 85 picoseconds with
six inches of leads attached the device. A 63' with six inches of leads has a round trip distance into
and out of the 63' of twelve inches. In 85 picoseconds, at the fastest velocity possible in the
universe, energy can only travel (0.0118 inches / picosecond X 85 picoseconds = 1.003 inches) 1.003
inches or about one-twelfth of the length of the 63' leads alone. This example points out the fact
that a “reality check” will help to smoke out bogus sales claims.
© Copyright 2010 Surge Suppression Incorporated® www.surgesuppression.com
56
The importance of having a 63' that has a small physical size and which allows it to be
connected with a minimum of lead length should become apparent. Thus, smaller and more compact
63' designs are preferred over large bulkier 63' designs which can not be positioned, mounted
and connected with a minimum of connected lead length.
63' Protection Modes
A 63' protection mode is a distinct pair of wires that is protected by the 63' For example, a
three-phase, four-wire plus ground wye distribution circuit has ten distinct modes or distinct conductor
pairs. They are L1-L2, L2-L3, L3-L1, L1-N, L2-N, L3-N, L1-G, L2-G, L3-G and N-G.
Protection modes are classified as normal modes or common modes. For ac power systems, the
normal modes include the hot (or phase or line) to the neutral (L-N) pair(s) and the phase-to-phase (or
hot-to-hot or line-to-line) pair(s).
For a three-phase, four-wire plus ground wye electrical system, there are six distinct normal mode
pairs. They are the three phase-to-phase pairs (L1-L2, L2-L3 and L3-L1) and the three phase-toneutral pairs (L1-N, L2-N, and L3-N). Common modes include those conductor pairs that involve
ground. For a three-phase, four-wire plus ground wye electrical system, there are four distinct
common mode pairs. They are neutral-to-ground (N-G) and the three line-to-ground pairs (L1-G, L2G, and L3-G). Thus, this circuit provides a total of ten distinct modes (six normal modes and four
common modes) or conductor pairs.
In the marketplace today, there are 63' designs sold to protect a ten mode, wye system that have
only three modes of protection circuitry (L1-N, L2-N, and L3-N), four modes of protection circuitry
(L1-N, L2-N, L3-N and N-G) and seven modes of protection circuitry (L1-N, L2-N, L3-N, L1-G, L2G, L3-G and N-G). These are “reduced mode” or “partial protection” 63' designs. Buying a
reduced mode or partial protection 63' design is like buying a bulletproof vest that only protects
your hands or feet. It will be beneficial, but it leaves a lot to be desired.
It is extremely difficult to separate the partial protection 63' designs from the true all mode
63' designs. A great deal of effort goes into camouflaging the specifications of the partial
protection units. Generally, the specifications for reduced mode 63' designs show let-through
voltages and other characteristic for all modes. They will state that all modes are protected. But, they
are reluctant to tell a customer which modes are not directly protected with distinct, dedicated,
independent protection circuitry and which modes have been left out. A 63' manufacturer should
honestly provide this data. The examination of an evaluation unit may be required to see what a
manufacturer is actually selling.
If a 63' specification sheet does not clearly state that there are dedicated protection components
and circuitry for each mode, avoid it. The limitations and problems of reduced mode 63' were
previously discussed and are well known to 63' design engineers.
As General Electric and Harris state, the best protection that you can get is to protect all modes
with dedicated protection circuitry. And, common sense requires that dedicated and independent
circuitry be placed where the transient voltages exist. The suppression circuitry can than equalize the
potentials and reduce them to lower harmless levels. Transients exist in all modes (as detailed in the
IEEE C62 Trilogy). Thus, all modes require dedicated and independent protection. This is also the
recommendation of ANSI/IEEE Std 1100-1999, the Emerald Book.
© Copyright 2010 Surge Suppression Incorporated® www.surgesuppression.com
57
Let-Through Voltage, Measured Limiting Voltage, or Surge Remnant Voltage
The let-through voltage (or measured limiting voltage or surge remnant voltage) is an important
measure of 63' performance. These measurements report the peak value of the surge remnant after
a 63' suppresses a specific surge. Thus, the measured limiting voltage or let-through voltage is the
residual voltage from an applied transient after the 63' operates. Smaller is better. The test
waveforms are prescribed by the Institute of Electrical and Electronic Engineers (IEEE), an
internationally recognized standards authority. The tolerances for these waveforms are on the order of
plus and minus ten per cent. This opens the door to unscrupulous manufacturers intentionally testing
at the minus ten percent surge current level to reduce their reported let-through voltages.
Beware of 63' specifications that provide "clamping voltages," a careful interpretation is
required. This may be a value determined by applying a small dc current, usually one milliampere,
and determining the voltage level at which the 63' begins to turn on. Secure the exact test
conditions. A dc value removes the effect of lead length and pulse response because the “di/dt” value
is zero in the equation “V = -L di/dt +ir.” This value is not the same as the dynamic impulse letthrough voltage and cannot be used to compare the dynamic response of 63' devices under surge
conditions. Thus, clamping voltage must be interpreted with caution.
To compare 63' let-through voltages, it is necessary to have full disclosure of the 63' lead
lengths, the test waveforms, measurement tolerances, measurement techniques and the points of
application of the transient on the ac power-frequency waveform. If the test conditions are not fully
disclosed, the tests cannot be duplicated and independently verified. Thus, no meaningful engineering
information is presented, just meaningless numbers on paper. To better understand the impact of
63' lead length, consider the example below in which one foot of wire is added to 63' leads. If
each 63' lead is increased by one foot the round trip distance (into and out of the 63') of the leads
is increased by two feet in total.
Example: Calculate the magnitude, ignoring polarity, of the surge voltage developed across one
foot of # 12 AWG wire when an IEEE 10,000 ampere, 8 X 20 µs current impulse is applied.
V = L di/dt + ir
V = (0.3 X 10-6 henries/ft)(1 ft)(10,000 A / 8 X 10-6 sec) + (10,000 A)(0.001588 ohms)
V = 375 volts + 15.88 volts = 390.88 volts
It is obvious that 63' lead length plays a major role in the performance of an installed and
operational 63' and shorter is better.
One 63' manufacturer allows 63' lead lengths of up to ten feet (or twenty feet round trip into
and out of the 63') in their installation instructions. This type of exceptionally long lead installation
is characteristic of physically large 63' units that are designed to impress the public with their size
rather than suppress transients. From the above example, we would increase the installed 63' letthrough voltage by (20 feet X 390.88 volts per foot = 7, 818 volts) 7,818 volts! At this point, it is
likely that the sensitive downstream-connected equipment would blow first and protect this 63'. It
is important to note the physical size of a 63' and read the 63' installation instructions. And, it is
important to determine if the unit can be physically installed with short lead lengths and to determine
if the 63' manufacturer really understands the physics of surge suppression.
Be alert to the fact that the $16,UL1449 7KLUG Edition suppressed voltage ratings (SVR) do
notnecessarily reflect "as installed lead length" performance measurements. The UL standardWest
© Copyright 2010 Surge Suppression Incorporated® www.surgesuppression.com
58
conditions require six inches of leads extending outside of the 63' enclosure. For example, modular
type 63'V, with UL listed modules may be tested at the connections to the module. This is a
nonfunctional configuration with zero lead length. Since module data is being presented, the hidden
assumption that the modules can be made to work with zero lead length is made. To obtain a
functional unit, the modules are plugged into an electrical housing that contains circuitry leading to
wire terminals used for the installation. The 63' housing is mounted on the wall next to an
electrical panel and the 63' is connected to the panel with wires running through approved conduit.
Once the wires are inside of the panel, they are run to circuit breakers or busses as required. Thus, a
significant amount of wiring and circuitry has to be added to the modules (or a physically large 63')
to provide an installed and functional 63'. The result of "at the module" or "at the lug" test data is
an intentional and significant understatement of actual installed 63' performance. Thus, actual "as
installed lead length" field performance will fall far short of the advertised module values. As shown
above, the "as installed lead length" is important because 63's are designed to deal with fast
rise time, short duration, and high peak amplitude events. Under these conditions, the inductive effects
of the connected wiring become significant. We are not looking at low-frequency ac circuit behavior.
UL 1449 UG Edition uses broad voltage categories. And, while a 93R rating between units may
appear significant, the actual measured data may be a few volts apart and could be the result of normal
measurement tolerances. It is better to rely on actual test data.
Ethical manufacturers test and publish certified test data in accordance with $16,UL 1449 UG
Edition and the IEEE C62 “Trilogy” series of standards on an "as installed lead length" (6 inches of
lead length outside of the device enclosure) basis. In all cases, the exact test conditions, as well as the
lead lengths should be specified. If the test conditions are not completely specified, the data is useless.
It is also important to note at what point on the sine wave the testing was conducted. Testing at 90
degrees and 180 degrees are common. For threshold or fixed clamping 63', testing at 90 degrees is
popular. For ring wave transients and a fixed clamping 63', everyone looks like a genus at 90
degrees. This is true because testing at 90 degrees will produce the minimum transient amplitude for
ring wave transients when testing a fixed clamping 63'. 63' that are not sine wave trackers or are
weak trackers all look the best when tested at 90O. When transients are applied at 90 degrees, the
transient is closest to fixed or threshold suppression point of the 63'. This type of testing conceals
the weaknesses of ring wave suppression. Everyone looks like a genius at 90 degrees. Also,
determine if the test wave was positive or negative going transient, as tests conducted with different
polarities may produce different results.
The IEEE has established three broad location categories relative to physical locations from the
electrical service to deep within a facility. Location Category “A” is the least severe, Category “B” is
more severe and Category “C” is the most severe location. For each of the location categories, the
IEEE has established standard transient waveforms. These standard transients are representative types
and amplitudes of transients expected at the various locations. It is important to ensure that a given
63' is recommended by the manufacturer for the location where it will be installed.
Peak Surge Current
This is a statement of the single shot peak surge current a 63' device can handle without
degradation or failure. Typically, this data will be presented by mode, by phase and/or total. High
peak surge current ratings are most important at service entrance (Category C) installations. That is
where one could expect to receive the largest surge currents, such as from a lightning strike. In
general, a 63' with a high peak surge current rating (in the region of three million surge
amperes total) will have a high let-through voltage. This is true because the unit must be physically
large which increases internal and external circuit path lengths and the let-through voltages.
© Copyright 2010 Surge Suppression Incorporated® www.surgesuppression.com
59
Physically smaller 63', with lower peak surge current 63' ratings, and shorter internal and
external circuit paths usually have lower let-through voltages.
The higher let-through of a stronger 63' unit is perfectly acceptable. The smaller 63' units
downstream will reduce the let-through voltages of the service entrance 63' to harmless levels.
Per NEMA LS-1, this data may be obtained from the component manufacturer’s tested values and
published specifications and “engineering formulations” or calculations. Additionally, it may in some
cases, be directly measured by a properly equipped and certified laboratory.
Peak Surge Current per Phase
There is no standard method of stating peak surge current “per phase.” Some total the L-N and LG modes. Some total the L-N modes and L-G modes and add in the N-G mode. The correct method of
determining “peak surge current per phase” is to determine the total peak surge current for the entire
unit, subtract the N-G value and divide this result by the number of phases. This method properly
includes the proper modes, avoids double counting and eliminates the N-G mode which normally
plays no role in suppressing transients referenced to the phase conductors. Alternatively, the peak
surge current per phase may be determined by adding one L-L, one L-N and one L-G peak surge
current value. This method properly accounts for the correct modes, eliminates double counting and
eliminates the N-G mode to obtain the proper per phase peak surge current rating. This can be a point
of confusion and make it difficult to evaluate 63's.
When a manufacturer provides the “peak surge current” for each mode and identifies the
independently protected modes and the total peak surge current for the entire unit, the device design
and peak surge current per phase may be determined with confidence and without double counting.
Energy Dissipation
This is an indication of the maximum amount of energy, measured in joules (watt-seconds) that a
63' device can dissipate. The presentation of this parameter on a 63' specification sheet is
subject to manipulation and exaggeration.
For example, a V130LA20B (20 mm diameter MOV) is rated at 70 joules maximum energy
dissipation for a 10X1000 µs impulse at 85O C. If the same component is subjected to a current of
0.001 amperes, it will clamp at a minimum voltage of 184 volts. Now suppose that the time increment
is one year, or (60sec/min)(60min/hr)(24 hr/day)(365days/year) = 31,536,000 seconds. The energy
dissipated by the component will be:
Energy (in joules) = e(volts)i(amps)t(seconds)
Energy (in joules) = (184 volts)(0.001 amperes)(31,536,000 sec) = 5,802,624 joules
Which value of energy dissipation is correct? They both are. Thus, a 63' manufacturer could
properly advertise either value. Obviously, 63' energy dissipation must be interpreted with caution.
It is best to ignore the energy dissipation data and use peak surge current per mode and total 63'
peak surge current as a measuring stick.
© Copyright 200 Surge Suppression Incorporated® www.surgesuppression.com
60
Noise (Frequency) Attenuation
This indicates the effect of the 63' device on a given frequency. It is usually provided in terms
such as -3 to -44db Common Mode Noise Rejection (CMNR), -3 to -36 dB Normal Mode Noise
Rejection (NMNR). A larger negative number is better. These values may also be stated as positive
“attenuation” values in decibels. A larger positive number is better.
As previously discussed, this data is presented based upon the Mil-Std-220A, the 50 ohm insertion
loss method. As previously demonstrated this data is totally useless and irrelevant for power
distribution system applications, due to the impedance level of these circuits. Many years ago, a
couple of 63' manufacturers began to tout the data. So, the 63' industry was forced to publish
this meaningless data.
Filter Frequency Range
This is the range in which the filter in the 63' device operates. It is usually provided in terms
such as 400 kHz to 30 MHz (CMNR), 450 Hz to 30 MHz (NMNR). Again, this data is presented
based upon the Mil-Std-220A, 50 ohm insertion loss method, measurements. This data is totally
useless and irrelevant for power distribution system applications, as previously demonstrated.
Altitude
This is a measurement of the altitude limit of the 63' device's operational range. This
measurement is normally only important to devices containing gas discharge tubes or neon indicators
because they are sensitive to pressure and by altitude. If using an altitude rated 63', the higher
number is better.
Life Expectancy or Pulse Life
This is a rating that has attracted sales interest. It is supposed to be an indication of how long you
can expect a 63' device to operate under field conditions. Data is normally provided in terms of
pulse life, such as 1,000 - 8/20µs Category C impulses without drift. A longer pulse life is better.
Not all manufacturers provide this information. The reasons include the required testing time, the
testing cost and the rapid introduction of new models in the 63' marketplace. However, per NEMA
LS-1, manufacturers are at liberty to use component manufacturers’ tested data and/or “engineering
formulations” (calculations) to provide this information.
The 63' manufacturer’s warranty provides the strongest statement of the confidence that the
manufacturer places in the products. This is based, not just upon the pulse life of the suppression
circuitry, but upon all the 63' subsystems, all of the circuitry, diagnostic systems and components.
Each manufacturer knows how long their products will last. The duration of a full replacement
warranty does not place “life expectancy” or “pulse life” limitations upon the end-user, during the full
replacement warranty period.
Thus, the length of a full replacement warranty is an indication of how long the manufacturer
expects the device to last. And, more importantly the end-user knows how long the transient
protection will be provided.
© Copyright 200 Surge Suppression Incorporated® www.surgesuppression.com
61
Warranty
This data indicates how long the manufacturer will replace the device free of charge to you if it
should sacrifice (fail) in use. Most quality manufacturers will replace the device or modules and
subassemblies during the warranty period. The longer and stronger the warranty and warranty period,
the better it is for the end-user. This provides lower annual costs and life cycle costs. Some
warranties are without cost only for part of the warranty period. For the remainder of the period, you
share the cost. Warranties that are for “defects in workmanship or materials” only may become a
problem for the end-user. If a catastrophic surge destroys any evidence of these “defects” and leaves
the end-user with damaged equipment, how does the end-user obtain a replacement unit?
Read 63' warranties that provide for the repair of equipment connected to the 63' device that
is damaged by the surge very carefully. Especially, read the “fine print.” It is better to have a 63'
device with a history of allowing no damaging surge to reach your equipment than to have a device
that will permit damage to your equipment even if the warranty pays for damage costs. The downtime
you experience and the frustration of having to get equipment repaired are factors to be considered.
To determine the value of the warranty, divide the cost of the 63' device by the years of the
warranty to determine the annual cost of the device. A device costing $1770 with a twenty-five year
warranty costs $70.80 per year. A device that only costs $885 with a five-year warranty actually costs
$177 per year. When the life cycle cost is computed based upon the longest “full replacement
warranty period,” the cost differences are very dramatic. The 63' with the twenty-five year
warranty has twenty-five life cycle costs of $1770. The 63' with the five-year warranty has a
twenty-five year life cycle cost of $4,425.
© Copyright 20 Surge Suppression Incorporated® www.surgesuppression.com
62