Brainscape's Knowledge GenomeTM

Browse over 1 million classes created by top students, professors, publishers, and experts.


See full index

Electrical Definitions > Chapter 2 Cables and conductors > Flashcards

Chapter 2 Cables and conductors Flashcards

1
Q

What is a conductor?

A

A conductor is a material which offerrs a low resistance to a flow of current.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
2
Q

Everyday conductors must be of

A

Low electrical resistance

Mechnically strong and flexible

and relatively cheap

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
3
Q

An insulator is?

A

An insulator is a material which offers a very high resistance to a flow of current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
4
Q

What should an insulator have ?

A

Certain electrical,mechanical,physical and chemical properties

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
5
Q

Electrical properties

A

Must have a high resistance

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
6
Q

Mechnical properties

A

It must be capable of withstanding mechnical stress like compression

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
7
Q

Physical properties

A

non- absorbent and capable of withstanding high temperatures

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
8
Q

Chemical properties

A

withstanding corrosive effects of chemicals

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
9
Q

Types of insulators ?

A

Rubber, pocelain,polyvinyl chloride paper , wood, plastic

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
10
Q

Types of conductors are?

A

Gold, sliver, copper, iron ,aluminium

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
11
Q

A cable is

A

A length of insulated conductor or group of conductors used to carry current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
12
Q

Two basic parts of cable?

A

Conductor and Insulator

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
13
Q

Types of Cables

A

Polyvinyl chloride cable
Multi- core cable
tough - rubber sheathed
Earth continuity conductor cable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
14
Q

Note:

A

The current rating in a cable decreases as temperature increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
15
Q

The current density

A

The amount of current which the conductor can safely carry without heating per unit cross sectional area.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
16
Q

The resistance that a conductor offers are determined by

A

The length of conductors
cross - sectional area
Type of material etc

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
17
Q

Temperature coefficient:?’

A

This is for coeffient of a material is the increase in the resistance of , 1ohm of that material when it is subject to the rise of temperature.

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
18
Q

Positve temperature coefficient

A

copper and aluminium resistance/ increases as temp increases

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
19
Q

Negative temperature coefficient

A

Carbon and electrolytes /resistance decrease as temp increase

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
20
Q

resistivity

A

The resistance of unit cube of a material measured on opposite faces of a cube= pL/a

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
21
Q

Temperature coefficient

A

R2/R1 = 1 + 0.004 x 30
= 1 + 0.004 x 20

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
22
Q

When is trunking used

A

In conditions where the cables are too large for using conduit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
23
Q

Resistance

A

The friction a material presents to a flow of current

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
24
Q

Voltage Drop -

A

The reduction in voltage in a circuit

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
25
Q

Domestic installation

A

supplied from a 16mm2 three coree amoured cable

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
26
Q

Note :

A

Trucks and ducts must be fixed and protected against corrosion

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
27
Q

temporary installation

A

an installation with an expected period of three months

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
28
Q

A circuit

A

a group of conductors for the purpose of carrying curent

How well did you know this?
1
Not at all
2
3
4
5
Perfectly
29
Q

Consumer’s terminals

A

The point of connection of the consumers’ conductors to the supply Authority meter .

30
Q

Purpose of testing an installation

A

To dectect faults in the installation before dangerous situations arisen

31
Q

types of protection

A

Elecromagnet
Fuse
Thermal

32
Q

Final sub circuit

A

connected to the distrubution board to supply electrical energy

33
Q

A installation needs to be protected from

A

Eaarth leakage , danger of electric shock, excess current and corrosion

34
Q

Electrical installation test

A

Visual inspection of workmanshop.

Verification of polarityi

Insulation resistance test

Testing for effective grounding

Continuty test

35
Q

what is a tool?

A

ppowered by human muscles rather than motors and engines

36
Q

why do you put switch gear in an installation

A

To protect cuircuits against excess current , earth leakage

37
Q

Note:

A

If a current passed through a conductor, the temperature of that conductor increases

38
Q

Units of electrical energy

A

The joule (J) and kilo-watt-hour (kWh)

39
Q

Joules =

A

Watts x seconds

40
Q

Kilowatt

A

energy consumed when one kilwatts is used for one hour.

1 kWh = 3,600,000J

41
Q

to convert 0f to 0c subtract 32 and multiply by 5 /9

A

to convert 0c to 0f multiply by 9/5 and add 32

42
Q

Wattmeter

A

measures the electrical power in a circuit

43
Q

ohm meter

A

The ohm is used to measure smaller values of resistance

44
Q

NOTE

A

If a current passes through a coil an electromagnet will be produced

45
Q

Difference between single bell and trembler

A

the trembler has a set of variable contacts

46
Q

types of indicator element

A

1) The pendulum type element
2) mechanical replacement type element
3)electrical replacement type element

47
Q

Purpose of the electric cell is?

A

To .change chemical energy into electrical energy

48
Q

Electrolyte

A

A liquid which changes its composition when a current passes through it

49
Q

Simple Lechanche Cell

A

Glass container
Electrolytes - sal ammoniac
Carbon plate - (+ ve electrode)
Zinc plate - (+ ve electrode)

50
Q

Leclanche cell has two main faults

A

Local action and polarization

51
Q

Local action

A

corroding of electrode

52
Q

Polarization

A

hydrogen bubbles resisting flow of current

53
Q

two modification Leclanche cells

A

Zinc electrode coated with mercury

carbon plate +ve surrounded with depolarising agent

54
Q

A Lechanche is termed primary cell when?

A

because it cannot be recharged chemically

55
Q

Advantages and disadvantages Leclanche

A

adv - (1) Cheap
requires little maintainance

disadv - It is not portable in the form

cell cannot be used over and over again .

56
Q

Effects of polarization

A

Incapable of supplying heavy currents

Having a high internal resistance

57
Q

Lead- Acid cells

A

is secondary because it can be charged electrically

58
Q

Methods of charging batteries

A

Trickle charge

Constant current

Constant Voltage

Floating system

59
Q

precaution

A

Always add acid to water not water to acid

Fire-fighting appliances should be handyd

room must be well ventilated

60
Q

Find internal resistance

A

subtract the closed curcuit voltage from open circuit voltage and divide by circuit current

r= E-V/I

61
Q

What is a service line?

A

Any electric conductor through which energy is supplied by the commission to the consumer

62
Q

Raceway

A

An enclosed channel that forms the path of electrical conductors to prevent them from heat moisture and dust

63
Q

Advanatages of using EMT over PVC

A

1)EMT is more durable than PVC
2)EMT is fire resistant where as pvc isn’t
3)EMT has high mechanical strenth where as pvc has physical weakness

64
Q

Differences between a circuit breaker and fuse

A

1)Circuit breakers short circuit when there is an overload in current whereas fuses melt

2)Circuit breaker can be reused over again whereas fuse is a one time use

3) Circuit breaker are safer than fuse because its a flip of a switch

4)Circuit breakers do not have exposed live parts where as fuses do

65
Q

Effects of loose termination on a busbar

A

1)The current would not be able to effectively return to supply causing overheating

2) There will be a break or short circuit if connection fails

3)The electrical apparatus can be destroyed

66
Q

How high voltages from t and tec is reduced for supply to residential ?

A

Transmission - To step up the voltages to be transmitted over long distances

Distribution - To stepdown the voltage to be distributed to consumers from substation

67
Q

Relationships between protective device and circuit conductors

A

If there is an overload of current the protective device automatically short circuits stopping the flow of current.

68
Q

Raceway types

A

Conduct or trunking ducting

69
Q

Space factor

A

Space factor is the ratio of the space occupied by the cables to the total space inside the conduit.

70
Q
A

Electrical Definitions (3 decks)

Brainscape helps you reach your goals faster, through stronger study habits.
© 2024 Bold Learning Solutions. Terms and Conditions