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AC-Alternating Current
Electrical current that continually reverses direction, with this
change in direction being expressed in Hertz, or cycles per second.
Ampere
Quantitative unit of measurement of electrical current. Abbreviated
as Amp or A.
ANSI C62.41-1991
A technical Standard that characterizes the electrical power line
surge environment. Originally published by the Institute of Electrical and Electronic
Engineers as Standard IEEE 587 -1980, it was updated in 1991 and now recognized as an
American National Standard.
Capacitor
An electrical component which stores electrical charges. It consists
of two metallic plates separated by a dielectric (non-conducting) material. When used in
conjunction with other components it can provide a high-frequency filtering capability.
Clamping Level
This generally is used to describe the voltage level which causes
the surge diversion device to start to divert surge energy. A related, but more important
parameter is the Suppressed Voltage.
Response Time
The time it takes a surge protection device to switch from its
"off" condition to an "on", diverting mode. This occurs when a
incoming surge voltage exceeds the clamping threshold level of the MOV or other
suppression component. Organizations such as IEEE, NEMA and Underwriters laboratories
consider response time to be a non-issue since MOV’s, Avalanche diodes etc (and the
surge protectors that use them) have response times that are 100 to 1000 times faster than
any transient that they are likely to encounter.
Category C, B and A
Classes described by the ANSI Standard C62.41 that define the surge
waveforms that would be representative at various locations within a building. Category C
products are intended for use at the main service panel or distribution panels that
require large surge current handling capability. Category B defines mid-building, branch
panel situations while Category A defines the local service panel or specific equipment.
Combination Pulse
A high energy test pulse specified by ANSI C62.41-1991. Also called
a "unipolar pulse".
Common Mode Voltage
A voltage, that appears on the phase and neutral wires of the power
system when compared with the system ground wire.
Current
Current, expressed in units of amperes, or simply amps, is the flow
of electrons through a conductor. AC, or alternating current, is a current in which the
flow of electrons reverses periodically. In the United States the current reversal occurs
60 times a second.
EMI -
Electro-Magnetic Interference
Electrically induced noise or transients.
Energy
Maximum allowable energy (in joules) for a single impulse on a
10/1000 µs current waveform. Indicative of the maximum amount of energy that the
suppressor can dissipate. This energy is dependent upon three (3) variables:
Voltage, Current, and Time. Any variation of the three will effect this figure.
Filter
Consists of a combination of components that allows only certain
frequencies, or a band of frequencies, to pass.
Frequency
The frequency of alternating voltage is the number of times per
second that it changes polarity from positive to negative. In the United States, the power
line frequency is 60 Hertz, 60 cycles per second.
Ground
For safety reasons, electrical systems in the USA have a wire
connected to earth ground at the service entrance. This "ground" wire is run
along with the two current carrying wires.
Headroom
Headroom is the voltage difference between the peak of the 50/60
Hz power line sine wave voltage and the ‘Threshold voltage" of the MOV (or
other) suppression elements. A minimum spacing of 15% above the sine wave peak is
considered essential.
Hertz
The unit of frequency, one cycle per second of alternating current.
IEEE 587-1980, ANSI
C62.41-1991
A technical Standard originally published by the Institute of
Electrical and Electronic Engineers (IEEE) in 1980, updated in 1991, and now recognized as
an American National Standard.
Impedance
Similar to electrical resistance, since it is a measure of the
opposition to the flow of electrical current. Impedance is meaningful only for a changing
current and changes value as the frequency of the applied waveform changes.
Inductance
The property of an electrical component , which opposes the flow of
electric current. An inductor has the property of impedance, the opposition to the flow of
electric current.
Joule
A joule Is a measure of the energy contained in an impulse or
conversely it is a measure of the absorption capability of a surge protection device.1
joule = 1 watt x 1 second.
Let-Through Voltage
The residual transient voltage that would appear across equipment
after an upstream surge protection device has operated. It is important to remember that
the "let-through" voltage is the sum of the voltage drop across the surge
protector itself plus the voltage drops that appear across the wiring that connects the
protector to the power lines. The protector clamping voltage is only one part of the
let-through voltage and frequently is of secondary importance to the wiring drop.
Maximum
Operating Voltage:
Maximum allowable continuous sinusoidal
voltage (RMS) at 50-60hz. If suppressor is exposed to a continuous voltage higher than RMS
voltage stated in specification, the suppressor may suffer damage.
Measured
Limiting Voltage:
The maximum magnitude of voltage that is measured across the
terminals of the SPD during the application of impulses of specified wave shape and
amplitude.
MOV-Metal Oxide Varistor
In many respects a nearly ideal suppression component. In standby
mode, the MOV presents a very high resistance in shunt with the power line – drawing
negligible current. When an incoming transient exceeds a critical voltage threshold, the
MOV switches rapidly to a near "short-circuit" diverting mode -handling many
thousands of transient amperes. When the transient surge expires, the MOV components reset
instantly to the reset mode-ready to respond to future transients.
Modes of Protection
Refers to the presence of MOV (or other) components connected
between phases to neutral, phases to ground, neutral to ground and between phases.
Neutral
One of the wires used in the USA to distribute power within a
building. The neutral wire is generally bonded to earth ground at a building service
entrance, but unlike the ground wire, the neutral wire also carries load current.
Noise
A signal frequency(s) that may be riding on top of the power line
sine wave. A number of systems use the power lines to carry signals and data to other
locations. Attempts to filter out the "so called noise" may disrupt the current
or future operation of these systems. It is wiser to provide L/C filtering immediately in
front of sensitive equipment, if it is ever needed. It seldom is!
Normal Mode Voltage
Voltage appearing between the phase wires and neutral of the power
system wiring.
NRTL
Nationally Recognized Testing Laboratory, one example of which is
Underwriters Laboratories, Inc. (UL).
Peak Current – I
peak
A common measure, used by marketing people, to express the relative
peak current handling capability (8/20us)of a surge suppression device. Frequently, it
merely represents the peak current rating of an MOV multiplied by the number of MOV’s
in parallel. The "true" peak current rating of a protector requires a careful
assessment of the fuse characteristics, the number of parallel protection circuits, are
all of them monitored etc. Bellcore specifications to protect their Central Offices, a
highly computerized facility, have found and specified surge current values of 20kA, (8/20
us) waveform, to be satisfactory.
Phase Angle
The point on the sine wave at which a transient occurs. IEEE states
that transients can occur at any phase angle. It is important to be able to see
suppression device response to transients at varying phase angles.
Power
Power, in watts, is the product of voltage (in volts) and current
(in amps). Energy in joules is equal to power (in watts) multiplied by time (in seconds).
Resistance
A property of electrical conductors or electrical insulators which
characterizes their ability to conduct or resist the flow of electricity.
Ringwave
A low-energy test waveform specified by ANSI C-62.41-1991.
SPD
Surge Protection Device. Also referred to as TVSS (Transient Voltage
Surge Suppressor).
Suppressed Voltage Rating
SVR
Suppressed Voltage Rating is a rating based on the measured limiting
voltage determined during the transient-surge suppression test. UL 1449 2nd
edition designates the rating of a surge suppressor range from 330 volts up to 6 kV. SVR
ratings are not in themselves indicative of superior performance, since installation and
cabling play a critical role in overall performance.
Series Type Surge Protector
A form of surge protector which handles the continuous AC power line
current but opposes surge current flow toward the load. Series type surge protectors must
be rated to handle the continuous 50/60 Hertz current, hence they are seldom employed at
building entry or mid-building locations. See Shunt Type Surge Protectors.
Service Life
The number of surges of given magnitude that can be suppressed by
the suppressor, a measure of reliability.
Shunt Mode
Shunt type surge protector which divert large surge current directly
to ground, are not constrained by the continuous power line currents and thus are employed
effectively on power systems with capabilities exceeding 5000 Amps (rms).
Sine Wave
The waveform that appears on the AC power lines. The 50/60 Hertz
sine wave is a periodic voltage waveform that oscillates above and below a zero axis. When
displayed on an oscilloscope it appears as an undulating wave with voltage appearing on
the "y" axis and time on the "x" axis.
Single Phase
The portion of a power source that represents only a single phase of
the three phases that are often available.
Spike
See surge
Surge
A brief transient wave of voltage, current or power in an electrical
circuit, lasting for less than 1% of the power wave cycle duration.
Swell
A momentary voltage increase of the power line voltage, lasting up
to several seconds. A swell is not considered to be a transient over voltage, but the TVSS
device must operate at a level in excess of the peak voltage of the swell voltage.
Otherwise, the surge protector will be attempting to clip the power line 50/60 Hz waveform
and will sustain major damage. This necessary spacing is called headroom.
TVSS
Transient Voltage Surge Suppressor. Also called Surge protection
Device (SPD).
Transient
An abnormal over voltage of microsecond duration. Also called a
surge or spike.
UL
Underwriters Laboratories, Inc.
UL 1449 2nd
Edition
A safety testing specification for power line surge suppressors
based in large part on ANSI C62.41 and C62.45 Waveform and Testing Standards. UL 1449 2nd
Edition addresses the issue of "SLOW BURN" in which end-of-life failure of
suppression components could result in significant damage to the TVSS product.
Voltage Drop
The change in potential between two points in a circuit caused by a
current flow through components within a circuit.
Voltage Reference
A voltage point from which a measurement is taken.
Voltage Threshold
The voltage level at which the connected circuit changes its
response.
Watts
The unit of measure of actual power. Watts are the product of volts
times current.
Waveform
The graphic depiction of an electrical voltage, current or power,
typically versus time.
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