Circuit Protection

n Types of Fused Protection How to pull them

Fuses n Auto-fuse (blade type and Color coded) n Mini-fuse n Maxi-fuse A. TEST HOLES B. REMOVAL

Maxi-fuses n Combination blade / cartridge n Protects main circuits n Safer than fusible link n Cover fewer circuits than a fusible link n Often in Power Distribution box

Ceramic and Glass n Rated by current failure level n Three letter code for type and size n Glass style replaces ceramic n Caution in pulling

Two reasons for blowing Where do they blow?

New Circuits n What size of fuse should I install? n Use Watts law. Watts divided by volts ?

FUSIBLE LINKS n Lighter gauge wire than main conductor n Covered with special insulation n Protect Main circuits n Usually under hood

Fusible Links Repair n Location n Circuits protected n Insulation – Visual checks n Installing a new link – 4 wire sizes smaller (4 numbers larger) – Soldering

Fuses Male Pal fusesFemale Pal fusesBolt on Pal Fuses

Circuit Breaker n Why circuit breakers n Styles n Deterioration

TESTING CIRCUIT PROTECTION DEVICES n Must inspect closely n Type of failure determines cause n Best to use DVOM n Do not overload circuit by installing to large of fuse or tin foil n Connections must be tight n Do not use un-fused jumper wire

Electrical Components

Switches n Controls electrical current (N.O. or N.C.) n Single-pole, single throw (SPST) n Momentary Switch n Single-pole, double throw switch (SPDT) n Ganged Switch

Relays n Electromagnetic Switches (Relays) n Two Circuits –Control Circuit –Load Circuit n Magnetic field operates contacts n Late model relays are universal

TESTING RELAYS n Can use several methods to test n Must Check both circuits n Be careful using test light if relay is operated by computer n Can bench test if needed n Some relays have schematic on them n Must be correct resistance

SOLENOIDS n Electromagnetic device with a iron core n Does mechanical work n Core is moveable and does work n Can test with DVOM

n Usually used to control fan motor speeds n Resistance is changed by control of switch n Controls current to change speeds n Thermal fuse

Variable Resisters n Rheostats –Two terminals –Higher current n Potentiometer –Three terminals –Lower current n Many uses for variable types

The three types of circuit defects are: n Shorts n Grounds n Opens – poor connections

TESTING FOR CIRCUIT DEFECTS n DVOM IS BEST TO USE! n Must know circuit operation before can diagnose problem n Must know how to use equipment and which equipment to use.

Now, did he say, “Amps, Volts or Ohms”?