1. Level 2 Electrical and Electronic 3

2. Conductors and insulators.
A material that freely allows the passage of an electrical current is called a conductor, whereas a material that resists the flow of current is called an insulator.

3. Conductors and insulators
Factors affecting the resistance of a conductor.
Length of the conductor.
Cross sectional area
The material the conductor is made of
The temperature of the conductor

4. Factors affecting the resistance of a conductor.

5. What is the main conductor used in motor vehicles?
COPPER
Reasons why copper is preferred,
Very low resistance to electron flow.
Malleability. Describes a material that means it can be easily shaped.
Ductility. The property of a material that allows it to be drawn into wires.

6. The main insulator used is PVC because of its,
High resistance to electron flow.
Resistance to water, fuel, oil and other contaminants.

7. Conductors and insulators

8. Earth return
List the reasons why the vehicles chassis is used as the earth return circuit.
Cheaper, less wire is required
Lighter, less wire means less weight

9. Insulated earth return
List vehicles where the vehicle frame could not be used as the earth return.
Vehicles with composite bodies
Fuel and chemical tankers

10. Cable sizes.
The quoted size of a cable refers to the number of strands and the wire diameter.
Example. 9/0.3 = 9 strands of wire, each being 0.3mm diameter.
As a guide, a 0.3mm strand of wire will carry approximately 0.5 amps of current.

11. Cable sizes.
14/ amps General applications such as, side lights, indicators
28/ amps Headlamps, horn, heated windows.
65/ amps
84/ amps
97/ amps
120/0.3 60amps Charging wire from alternator to battery depending on alternator output
37/ amps Starter cable/ battery earth

12. List 2 reasons why it is important to select the correctly rated cable for each application.
To ensure enough power is supplied to the consumer with minimal losses
Over rating of the cable will increase vehicle weight and cost.

13. Fuses
a fuse contains a metal strip which is designed to overheat and melt when subjected to a specified excessive level of current flow, breaking the circuit and stopping the excessive current flow from potentially damaging the more valuable components and wiring.

14. circuit breakers.
Circuit breakers are not destroyed by excess current. A bimetallic strip heats up and bends, opening a set of contacts and breaking the circuit. Circuit breakers can be either manual or automatic reset types depending on the type of circuit they are protecting. Electric windows, window heaters

15. Blade fuse colours Current rating. Colour code. 3 Violet 4 Pink
Clear/beige
Brown
10 Red
15 Blue
20 Yellow
25 Neutral
30 Green

16. Electrical terminals and connectors
What is the meant by the term connectors?
Connectors join wires together
What is the meant by the term terminals?
Terminals are the point at which the cables connect to a component.

17. Electrical terminals and connectors

18. Relays.

19. Relay

20. Relay operation

21. Moving contact (Armature)
Simple Relay Components
Moving contact (Armature)
Fixed contact 2 4
Relay switches high currents.
Construction
Windings
Soft iron
core 1 3
Windings wrapped around iron core to form electromagnet.
Return
spring
Contains fixed and moving contacts.
Spring ‘returns’ moving contact to ‘home’ position.
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22. Simple Relay Operation
(one normally open contact)
Operation:
12V supply is available at switch.
Switch closes, magnetic field attracts armature, contacts close.
Current flows across contacts.
12V
Switch opens, return spring pulls contacts apart.
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23. 5 Pin Relay
N.C.
N.O.
COM
Contains 3 high current terminals: N.O., N.C. and COM, and 2 coil terminals.
Operation:
Current flows across N.C. and COM contacts when relay not energized.
Switch closes, magnetic field attracts armature, N.O. and COM contacts close.
Current flows across N.O. and COM contacts.
Switch opens, contacts return to home position.
Commonly found in automotive circuits.
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24. Briefly describe the operation of a relay
When a small current energizes the electro-magnet, it attracts an armature blade and closes contact points. Current can then flow across the points to power the main circuit.

25. Electrical faults. The 3 main faults to occur in motor vehicle wiring systems are;
Open circuit, where the circuit is broken and no current can flow.
Short circuit is where a fault has caused a wire to touch another conductor and the current uses this easier path to complete the circuit.
A high resistance in part of the circuit, such as a dirty connection, which will reduce the amount of current that can flow.