Glossary Of Terms
The following information is commonly used in the descriptions
of various electrical and electronic characteristics and standards
(including fuses). This information is only a guide and may
contain errors.
To find the information you require "click" on one
of the letters below
A B
C D E
F G H
I J K
L M N
O P Q
R S T
U V W
X Y Z
A
Ampere
The measurement of intensity of rate of flow of electrons
in an electrical circuit. An ampere is the amount of
current that will flow through a resistance of one ohm under
pressure of one volt. Top
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Ampere Rating
The current carrying capacity of a fuse, when a fuse is subjected
to a current above it's ampere rating, It will open the circuit
after a predetermined period of time. Top
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Ampere Squared Seconds (I2t)
The measure of heat energy developed within a circuit
during the fuse's clearing. It can be expressed as "melting
I2t", "arcing I2t"
or the sum of them as "clearing I2t".
"I" stands for effective let-through current (RMS),
which is squared, and "t" stands for time of opening,
in seconds.Top
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Arcing Time
The amount of time from the instant the fuse link has melted
until the overcurrent is interrupted, or cleared.
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B
Breaking Capacity
The rating which defines a fuse's ability to safely interrupt
and clear short circuits. This rating is much greater
than the anpere rating of a fuse. The NEC defines interrupting
rating as "The highest current at rated voltage that
an overcurrent protective device is intended to interrupt
under standard test conditions".
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C
Cartridge Fuse
A fuse consisting of a current responsive element inside a
fuse tube with terminals on both ends.
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Circuit Breaker Ratings
Type B - Small inrush or switching surges, heating loads,
tungsten lighting.
Type C - Moderate switching surges for short circuit (Eg.
discharge lamps).
Type D - High inrush applications.
Type K - Suitable for the protection of motors, transformers,
lamps & cables. Top
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Classes of Fuses
The industry has developed basic physical specifications
and electrical performance requirements for fuses with voltage
ratings of 600 volts or less. These are known
as standards. If a type of fuse meets the requirements
of a standard, it can fall into that class. Typical
classes are K, RK1, RK5, G, L, H, T, CC and J.
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Class CC Fuses
600V, 200,000 ampere interrupting rating, branch circuit
fuses with overall dimensions of 0.41mm x 1.5mm. Their
design incorporates a rejection feature that allows them to
be inserted into rejection fuse holders and fuse blocks that
reject all lower voltage, lower interrupting rating 0.41mm
x 1.5mm fuses. They are available from 0.01 amps to
30 amps. Top
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Class G Fuses
480V, 100,000 ampere interrupting rating branch circuit
fuses that are size rejecting to eliminate over-fusing.
The fuse diameter is 0.41mm while the length varies from 0.94mm
to 2.25mm. These are available in ratings from 1 amps
to 60 amps. Top
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Class H Fuses
250V and 600V, 10,000 ampere interrupting rated branch circuit
fuses that may be renewable or non-renewable. These
are available in ampere ratings of 1 amp to 600 amps.
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Class J Fuses
These fuses are rated to interrupt a minimum 200,000 amperes
AC. They are labelled as "Current Limiting",
are rated for 600Volts AC and are not interchangeable with
other classes. Top
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Class K Fuses
These are fuses listed as K-1, K-5 or K-9 fuses.
Each subclass has designated I2t and
Ip maximums. These are dimensionally the same as class
H fuses and they can have interrupting ratings of 50,000,
100,000 or 200,000 amps. These fuses are current limiting.
However, they are not marked "current limiting"
on their label since they do not have a rejection feature.
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Class L Fuses
These fuses are rated for 601 to 6000 amperes and are
rated to interrupt a minimum of 200,000 amperes AC.
They are labelled "current limiting" and are rated
for 600VAC. They are intended to be bolted into their
mountings and are normally used in clips. Some Class
L fuses have designed-in time delay features for all purpose
use. Top
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Class R Fuses
These are high performance fuses rated 1/10 to 600 amps
in 250 volt and 600 volt ratings. All are marked "current
limiting" on their label and all have a minimum of 200,000
amp interrupting rating. They have identical outline
dimensions with the Class H fuses But have a rejection feature
which prevents the user from mounting a fuse of lesser capabilities
(lower interrupting capacity) when used with special Class
R clips. Class R fuses will fit into either rejection
or non-rejection clips. Top
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Class T Fuses
An industry class of fuses in 300 volt and 600 volt
ratings from 1 amp to 1200 amps. They are physically
very small and can be applied where space is at a premium.
They are fast acting fuses, with an interrupting rating of
200,000 amps RMS. Top
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Clearing Time
The total time between the beginning of the overcurrent
and the final opening of the circuit at rated voltage by an
overcurrent protective device. Clearing time is the total
of the melting time and the arcing time. Top
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Current Limitation
A fuse operation relating to short circuits only.
When a fuse operated in its current limiting range, it will
clear a short circuit in less than 1/2 cycle. Also,
it will limit the instantaneous peak let-through current
to a value substantially less than obtainable in the same
circuit if a fuse were replaced with solid conductor
of equal impedance. Top
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D
DIN (Fuses)
Refers to fuses where the connection is by a solid blade,
usually copper. These blades can either be solid or slotted
to allow the fitting of these fuses into various holders &
mountings. Top
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Dual Element Fuse
Fuse with a special design that utilizes two individual
elements in series inside the fuse tube. One element, the
spring actuated trigger assembly, operates on overloads up
to 5-6 times the fuse current rating. The other element, the
short section, operates on short circuits up to their interrupting
rating. Top
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E
Electrical Load
That part of the electrical system which actually uses
the energy or does the work required.
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F
Fast Acting Fuses
A fuse which opens on overload and short circuits very
quickly. This type of fuse is not designed to withstand
temporary overload currents associated with some electrical
loads. Top
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Fuse
An overcurrent protective device with a fusible link that
operates and opens the circuit on an overcurrent condition.
Top
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Fuse Sizes (Semi-Conductor)
FERRAZ 30 = BUSSMANN 1*
FERRAZ 31 = BUSSMANN 1
FERRAZ 32 = BUSSMANN 2
FERRAZ 33 = BUSSMANN 3.
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G
gR
A term used in the description of fuses to indicate that
it has the characteristics to provide both short circuit & overload
protection. Top
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H
High Speed Fuse
A fuse with no intentional time-delay in the overload
range and designed to open as quickly as possible in the short
circuit range. These fuses are often used to protect
solid state devices. Top
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HRC fuse
HRC = high rupturing capacity.
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I
Inductive Load
An electrical load which pulls a large amount of current
(an inrush current) when first energized. After a few cycles
or seconds the current "settles down" to the full-load
running current. Top
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Interrupting Rating (Breaking Capacity)
The rating which defines a fuse's ability to safely interrupt
and clear short circuits. This rating is much greater
than the anpere rating of a fuse. The NEC defines interrupting
rating as "The highest current at rated voltage that
an overcurrent protective device is intended to interrupt
under standard test conditions".
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J
K
L
M
Melting Time
The amount of time required to melt the fuse link during
a specified overcurrent.
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N
"NEC" Dimensions
These are dimensions once referenced in the National Electrical
Code. They are common to Class H and K fuses and provide interchangeability
between manufacturers for fuses and fusible equipment of given
ampere and voltage ratings. Top
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O
Ohm
The unit of measure for electric resistance. An ohm is
the amount of resistance that will allow one ampere to flow
under a pressure of one volt..
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Ohm's Law
The relationship between voltage, current and resistance,
expressed by the equation V=IR, where V is the voltage
in volts, I is the current in amperes, and R is the resistance
in ohms. Top
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One Time Fuses
Generic term used to describe a Class H non-renewable
cartridge fuse, with a single element.
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Overcurrent
A condition which exists on an electrical circuit
when the normal load current is exceeded. Overcurrents take
on two seperate characteristics - overloads and short circuits.
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Overload
Can be classified as an overcurrent which exceeds
the normal full load current of a circuit, Also characteristic
of this type of overcurrent is that it does not leave the
normal current carrying path of the circuit, (that is it flows
from the source, through the conductors, through the load,
back through the conductors, to the source again). Top
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P-Q
Peak Let-Through Current, Ip
The instantaneous value op peak current let-through by
a current-limiting fuse, when it operates in it's current
limiting range. Top
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R
Renewable Fuses (600v & Below)
A fuse in which the element, typically a zinc link, may
be replaced after the fuse has opened, and then reused. Renewable
fuses are made to Class H standards.
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Resistive Load
An electrical load which is characteristic of not
having any significant inrush current. When a resistive load
is energised, the current rises instantly to it's steady-state
value, without first rising to a higher value. Top
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R.M.S. Current
The R.M.S. (root-mean-square) value of any periodic
current is equal to the value of the direct current which,
flowing through a resistance, produces the same heating effect
in the resistance as the periodic current does. Top
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S
Semiconductor Fuses
Fuses used to protect solid-state devices. (see High Speed
Fuses). Top
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Short Circuit
Can be classified as an overcurrent which exceeds
the normal full load current of a circuit by a factor of many
times (tens, hundreds or thousands greater). Also characteristics
of this type of overcurrent is that it leaves the normal current
carrying path of the circuit, (it takes a "shortcut"
around the load and back to the source).
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Short Circuit Rating
The maximum short-circuit current an electrical component
can sustain without the occurence of excessive damage when
protected with an overcurrent protective device.
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Single Phasing
That condition which occurs when one phase of a three
phase system opens, either in a low voltage (secondary) or
a high voltage (primary) distribution system. Primary or secondary
single phasing can be caused by a number of events. This condition
results in unbalanced currents in polyphase motors and unless
protective measures are taken, causes overheating and failure.
Top
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T
Threshold Current
The symmetrical RMS available current at the threshold
of the current-limiting range, where the fuse becomes current-limiting
when tested to the industry standard. This value can be read
off of a peak let-through chart where the fuse curve intersects
the A-B line. A threshold ratio is the relationship of the
threshold current to the fuse's continuous current rating.
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Time Delay Fuse
A fuse with a built in time delay that allows temporary
and harmless inrush currents to pass without opening, but
is so designed to open on sustained overloads and short circuits.
Top
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U
UR/UA
A term used in the description of fuses to indicate that
it has the characteristics to provide only Short circuit protection.
Top
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V
Voltage Rating
The maximum open circuit voltage in which a fuse can be
used, yet safely interrupt an overcurrent, Exceeding the voltage
rating of a fuse impairs it's ability to clear an overload
or short circuit safely.
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W
Withstand Rating
The maximum current that an unprotected electrical component
can sustain for a specified period of time without the occurrence
of extensive damage to that component.
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X-Y-Z
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