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Circuit Protection

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Circuit Protection

Types of Fused Protection

How to

pull them

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FusesAuto-fuse

(blade type

and Color

coded)

Mini-fuseMaxi-fuse A. TEST HOLES

B. REMOVAL

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Maxi-fusesCombination blade / cartridge

Protects main circuitsSafer than fusible link

Cover fewer circuits than a

fusible link

Often in Power Distribution box

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Ceramic and Glass

Rated by current failure level

Three letter code for type and size

Glass style replaces ceramic

Caution in pulling

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Two reasons for blowing

Where do they blow?

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New Circuits

What size of

fuse should I

install?

Use Watts law.

Watts dividedby volts

?

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FUSIBLE LINKS

Lighter gauge wire

than main

conductor Covered with

special insulation

Protect Main

circuits

Usually under

hood

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Fusible Links Repair Location Circuits protected

Insulation

Visual checks Installing a new

link

4 wire sizessmaller (4

numbers larger)

Soldering

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Fuses

Male Pal fuses Female Pal fuses Bolt on Pal Fuses

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Circuit Breaker

Why circuit breakers

Styles

Deterioration

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TESTING CIRCUIT

PROTECTION DEVICES Must inspect closely

Type of failure determines cause

Best to use DVOM

Do not overload circuit by installing

to large of fuse or tin foil

Connections must be tight

Do not use un-fused jumper wire

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Electrical Components

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Switches

Controls electrical

current (N.O. or N.C.)

Single-pole, singlethrow (SPST)

Momentary Switch

Single-pole, double

throw switch (SPDT)

Ganged Switch

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TESTING RELAYS

Can use several methods to test

Must Check both circuits

Be careful using test light if relay is

operated by computer

Can bench test if needed

Some relays have schematic on them

Must be correct resistance

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SOLENOIDS

Electromagnetic

device with a iron

core

Does mechanical

work

Core is moveable

and does work Can test with

DVOM

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Usually used to

control fan motor

speeds Resistance is

changed by control

of switch

Controls current to

change speeds

Thermal fuse

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Variable Resisters

Rheostats

Two terminals

Higher current

Potentiometer

Three terminals

Lower current

Many uses for

variable types

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The three types of circuit

defects are:

ShortsGrounds

Opens poor connections

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TESTING FOR CIRCUIT

DEFECTS DVOM IS BEST TO USE!

Must know circuit operation before

can diagnose problem

Must know how to use equipment

and which equipment to use.

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Now, did he say,

Amps, Volts or

Ohms?