Circuit Protection - Autoshop 101

1 Circuit PROTECTIONPage 1 Autoshop , All Rights Reserved. This Automotive SeriesCIRCUIT PROTECTIONhas been developed byKevin R. SullivanProfessor ofAutomotive TechnologySkyline CollegeAll Rights ReservedVisit us on the web: PROTECTIONC ircuit Protection devices are used to protect wires and connectors from being damaged byexcess current flow caused by an over current or short- Circuit . Excess current causes excessheat, which causes Circuit Protection to "open Circuit ". Circuit PROTECTIONPage 2 Autoshop , All Rights Protection DEVICESF uses, fuse elements, fusible links, and Circuit breakers are used as Circuit protectiondevices. Circuit Protection devices are available in a variety of types, shapes, and specificcurrent ratings.

2 FUSESA fuse is the most common Protection device. A fuse is placed in an electrical Circuit , so thtwhen current flow exceeds the rating of the fuse it "blows" or "blows out". The element inthe fuse melts, opening the Circuit and preventing other components of the Circuit frombeing damaged by the overcurrent. The size of the metal fuse element determines therating. Remember excessive current causes excess heat, and it's heat and not the currentthat causes the Circuit protector to open. Once a fuse "blows" it must be replaced with anew PROTECTIONPage 3 Autoshop , All Rights LOCATIONSF uses are located throughout the entire vehicle. Common locations include the enginecompartment, behind the left or right kick panels, or under the dash.

3 Fuses are usuallygrouped together and are often mixed in with other components like relays, Circuit breakers,and fuse BLOCK COVERSFuse / relay block covers usually label the location and position of each fuse, relay, and fuseelement contained PROTECTIONPage 4 Autoshop , All Rights TYPESF uses are classified into basic categories: blade type fuses or cartridge type fuses. Severalvariations of each are FUSE TYPESThe blade fuse and fuse element are by far the most commonly used today. Three differenttypes of blade fuses exist: The Maxi Fuse, The Standard ATO fuse, and the Mini fuse. Thefuse element has replaced the fusible link and will be explained later.

4 Circuit PROTECTIONPage 5 Autoshop , All Rights Reserved. BASIC CONSTRUCTIONThe blade type fuse is a compact design with a metal element and transparent insulatinghousing which is color-coded for each current rating. (Standard ATO shown below: howeverconstruction of both the mini and maxi fuses are the same.)FUSE AMPERAGE COLOR RATINGFuse amperage color ratings for both the mini and standard ATO fuses are , the amperage color ratings of maxi fuses use a different color Ratings For STANDARD and MINI FusesFuse Amp RatingIdentification PROTECTIONPage 6 Autoshop , All Rights Ratings For MAXI FusesFuse Amp RatingIdentification Color20 Yellow30 Green40 Amber50 Red60 Blue70 Brown80 ColorlessCIRCUIT PROTECTIONPage 7 Autoshop , All Rights TYPE FUSESMany older vehicles, both foreign and domestic, use glass or ceramic fuse cartridges thatwere either color coded or stamped on case for current ratings.

5 Glass fuses were used onolder domestic vehicles while the ceramic were used on most older European fuses have an amperage color rating system while glass fuses have the amperageratings stamped into one of the metal end LINKS AND FUSE ELEMENTSF usible links are divided into two categories: the fuse element cartridge and the fusible construction and function of fusible links and fuse elements are similar to that of a main difference is that the fusible link and fuse element are used to protect higheramperage electrical circuits, generally circuits 30 amps or higher. As with fuses, once afusible link or fuse element blows out, it must be replaced with a new one.

6 Circuit PROTECTIONPage 8 Autoshop , All Rights ELEMENT CARTRIDGEFuse elements, a cartridge type fusible link, are also known as a Pacific fuses. The elementhas the terminal and fusing portion as a unit. Fuse elements have replaced fusible links forthe most part. The housing is color coded for each current rating. Although, fuse elementsare available in two physical sizes and are either plug in or bolt on design, the plug-in typeis the most ELEMENT CARTRIDGE CONSTRUCTIONC onstruction of the fuse element is quite simple. A colored plastic housing contains thefusing portion element which can be viewed through a clear top. Fuse ratings are alsostamped on the PROTECTIONPage 9 Autoshop , All Rights ELEMENT COLOR IDENTIFICATIONFuse amperage color ratings are shown below.

7 The fusing portion of the fuse element isvisible through a clear window. The amperage ratings are also listed on the fuse Element Color Ratings - PacificAmperage RatingIdentification Color30 Pink40 Green50 Red60 Yellow80 Black100 Blue Circuit PROTECTIONPage 10 Autoshop , All Rights Reserved. FUSIBLE ELEMENTSF usible elements are often located near the battery by themselves. FUSIBLE ELEMENTSF usible elements can also be located in relay / fuse boxes in the engine PROTECTIONPage 11 Autoshop , All Rights LINKSF usible links are short pieces of a smaller diameter wire designed to melt during an overcurrent condition. A fusible link is usually four (4) wire sizes smaller than the Circuit that it isprotecting.

8 The insulation of a fusible link is a special nonflammable material. This allowsthe wire to melt, but the insulation to remain intact for safety. Some fusible links have a tagat one end that indicates its rating. Like fuses, fusible links must be replaced after theyhave "blown" or melted opened. Many manufacturers have replaced fusible links with fuseelements or maxi fuses. Circuit BREAKERSC ircuit breakers are used in place of fuses for the Protection of complicated power circuitssuch as the power windows, sunroofs and heater circuits. Three types of Circuit breakersexist: The manual reset type - mechanical, the automatic resetting type - mechanical, andthe automatically reset solid state type - PTC.

9 Circuit breakers are usually located inrelay/fuse boxes; however, some components like power window motors have circuitbreakers built PROTECTIONPage 12 Autoshop , All Rights BREAKER CONSTRUCTION (MANUAL TYPE)A Circuit breaker basically consists of a bimetal strip connected to two terminals and to acontact in between. Manual Circuit breaker when tripped (current flow beyond its rating) willopen and must be reset manually. These manual Circuit breakers are called "non-cycling" Circuit BREAKER OPERATION (MANUAL TYPE)The Circuit breaker contains a metal strip made of two different metals bonded togethercalled a bimetal strip. This strip is in the shape of a disc and is concaved downward.

10 Whenheat from the excessive current is higher than the Circuit breaker current rating the twometals change shape unevenly. The strip bends or warps upwards and the contacts open tostop current flow. The Circuit breaker can be reset after it is PROTECTIONPage 13 Autoshop , All Rights Reserved. MANUAL RESET TYPEWhen a Circuit breaker is opened by an over-current condition, the Circuit breaker requiresreset. To do so, insert a small rod (paper clip) to reset the bimetal plate as shown below. AUTOMATIC RESETTING TYPE - MECHANICALC ircuit breakers that automatically reset are called "cycling" Circuit breakers. This type ofcircuit breaker is used to protect high current circuits, such as power door locks, powerwindows, air conditioning, etc.