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CIRCUIT PROTECTION
This Automotive Series
CIRCUIT PROTECTION
has been developed by
Kevin R
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autoshop101
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Excess current causes excess
heat, which causes circuit protection to "open circuit"
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com, All Rights Reserved
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Circuit protection devices are available in a variety of types, shapes, and specific
current ratings
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A fuse is placed in an electrical circuit, so tht
when current flow exceeds the rating of the fuse it "blows" or "blows out"
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The size of the metal fuse element determines the
rating
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Once a fuse "blows" it must be replaced with a
new one
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Common locations include the engine
compartment, behind the left or right kick panels, or under the dash
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FUSE BLOCK COVERS
Fuse / relay block covers usually label the location and position of each fuse, relay, and fuse
element contained within
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Several
variations of each are used
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Three different
types of blade fuses exist: The Maxi Fuse, The Standard ATO fuse, and the Mini fuse
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© Autoshop 101
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CIRCUIT PROTECTION
BASIC CONSTRUCTION
The blade type fuse is a compact design with a metal element and transparent insulating
housing which is color-coded for each current rating
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FUSE AMPERAGE COLOR RATING
Fuse amperage color ratings for both the mini and standard ATO fuses are identical
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Color Ratings For STANDARD and MINI Fuses
Fuse Amp Rating
Identification Color
3
Violet
5
Tan
7
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Glass fuses were used on
older domestic vehicles while the ceramic were used on most older European vehicles
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FUSIBLE LINKS AND FUSE ELEMENTS
Fusible links are divided into two categories: the fuse element cartridge and the fusible link
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The main difference is that the fusible link and fuse element are used to protect higher
amperage electrical circuits, generally circuits 30 amps or higher
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© Autoshop 101
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CIRCUIT PROTECTION
FUSE ELEMENT CARTRIDGE
Fuse elements, a cartridge type fusible link, are also known as a Pacific fuses
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Fuse elements have replaced fusible links for
the most part
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Although, fuse elements
are available in two physical sizes and are either plug in or bolt on design, the plug-in type
is the most popular
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A colored plastic housing contains the
fusing portion element which can be viewed through a clear top
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© Autoshop 101
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CIRCUIT PROTECTION
FUSE ELEMENT COLOR IDENTIFICATION
Fuse amperage color ratings are shown below
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The amperage ratings are also listed on the fuse element
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FUSIBLE ELEMENTS
Fusible elements can also be located in relay / fuse boxes in the engine compartment
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A fusible link is usually four (4) wire sizes smaller than the circuit that it is
protecting
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This allows
the wire to melt, but the insulation to remain intact for safety
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Like fuses, fusible links must be replaced after they
have "blown" or melted opened
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CIRCUIT BREAKERS
Circuit breakers are used in place of fuses for the protection of complicated power circuits
such as the power windows, sunroofs and heater circuits
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Circuit breakers are usually located in
relay/fuse boxes; however, some components like power window motors have circuit
breakers built in
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Manual circuit breaker when tripped (current flow beyond its rating) will
open and must be reset manually
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CIRCUIT BREAKER OPERATION (MANUAL TYPE)
The circuit breaker contains a metal strip made of two different metals bonded together
called a bimetal strip
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When
heat from the excessive current is higher than the circuit breaker current rating the two
metals change shape unevenly
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The circuit breaker can be reset after it is tripped
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To do so, insert a small rod (paper clip) to reset the bimetal plate as shown below
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This type of
circuit breaker is used to protect high current circuits, such as power door locks, power
windows, air conditioning, etc
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The bimetal strip will overheat and open from the excess current by an overcurrent
condition and is automatically reset when the temperature of the bimetal strip cools
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When heat from the excessive current is higher than the
circuit breaker current rating the two metals change shape unevenly
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With no current flowing the bimetal
strip cools and returns to its normal shape, closing the contacts and resuming the current
flow
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© Autoshop 101
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CIRCUIT PROTECTION
AUTOMATIC RESETTING SOLID STATE TYPE - PTC
A Polymer PTC (for Positive Temperature Coefficient) is a special type of circuit breaker
called a thermistor (or thermal resistor)
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PTCs, which are made from a conductive polymer, are solid state
devices, which means they have no moving parts
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POLYMER PTC CONSTRUCTION AND OPERATION
In its normal state, the material in a polymer PTC is in the form of a dense crystal, with
many carbon particles packed together
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This resistance is low
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In this expanded "tripped" state,
there are few pathways for current
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It resets only when voltage is removed and the polymer cools
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