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Pre-Employment Electrician Theory > Conductors 030104b > Flashcards

Conductors 030104b Flashcards

1
Q

What is soft-drawn copper for?

A

Soft-drawn copper is durable, pliable and easy to work with. Used for most insulated conductors within a building.

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2
Q

What are medium and hard-drawn copper used for?

A

Used for aerial distributions as well as high voltage distribution and switchgear.

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3
Q

What are some copper applications?

A

Conductors for buildings and plants.
Busbars for splitters, motor control centres (MCCs) and panelboards.
Windings for motors, relays, contactors and transformers.

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4
Q

What is aluminum mainly used for and why?

A

Used for outdoor overhead service conductors as well as underground due to the lower cost and light weight.
Also used for transformer windings and busways.

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5
Q

What is steel wire mainly used for?

A

Used to reinforce aluminum wire since aluminum has a low tensile strength.
Is in the centre of aluminum high voltage cable and called aluminum conductor steel-reinforced (ACSR).

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6
Q

What kind of conductor is used sometimes as a coating for busbars in splitters, switchgear and panelboards?

A

Silver and Tin.

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7
Q

What is used for high-quality audio speaker cables?

A

Silver coated conductors since they are the least resistive of the metal conductors.

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8
Q

What is used to plate terminations?

A

Gold and Silver.

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9
Q

Which type of conductor may have a rectangular or a circular cross-section?

A

Solid conductors.

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9
Q

Which conductor may have a rectangular or a circular cross-section?

A

Solid conductors.

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10
Q

What are rectangular conductors used for?

A

Busbars in splitters, circuit breaker panels and blade type switch contacts in large switches.

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11
Q

What are circular conductors used for?

A

Often covered with electrical insulation and used for pulling into raceways and conduits.

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12
Q

How many strands are normally in a stranded conductor?

A

Can consist of 7, 19, 37, 61, 91 or 127 strands.

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13
Q

Which stranded cable is more flexible?

A

Generally the more strands the more flexible the cable will be.

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14
Q

What are finer stranded cables used for?

A

High vibration areas like motors or generators or where moving equipment is involved like overhead cranes.

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15
Q

What makes a good conductor vs a poor conductor?

A

The more free electrons per cubic cm.

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16
Q

What metal is the best conductor?

A

Silver.

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17
Q

What is tungsten used for?

A

Filaments in incandescent lamps.

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18
Q

What is nichrome used for?

A

Electric heater elements.

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19
Q

What are some examples of insulating materials?

A

Glass, rubber, mica, plastics, oil, paper, cotton, silk and air.

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20
Q

What factors matter when selecting an insulating material?

A

Ambient temperature
Voltage level of the installation.
Physical protection requirements.

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21
Q

What does dielectric strength refer to?

A

The insulating strength of a material.

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22
Q

Can all insulators become conductive?

A

Yes. If enough energy or strong enough voltage is applied to an insulator it can force it to conduct.

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23
Q

What is the dielectric strength of a material measured in?

A

volts-per-millimetre.

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24
Q

What has the lowest dielectric strength?

A

Air at 3 kV/mm

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25
Q

What has the highest dielectric strength?

A

Mica at 160 kV/mm

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26
Q

What are two examples of a semiconductor?

A

Silicon and germanium.

27
Q

What is Silicon and germanium used for?

A

Used for the manufacture of solid-state electronic devices.

28
Q

What do silicon rectifiers do?

A

Used to change alternating current to pulses of direct current. Will allow the the rectifier to act as a insulator or conductor depending on the direction of the applied voltage.

29
Q

What factors can affect the resistance of a conductor?

A

M.A.L.T.
Material Type
Area(Cross-sectional)
Length of the conductor
Temperature of the material.

30
Q

Is resistance higher or lower in a longer cable?

A

The longer the cable the higher the resistance. The resistance of a conductor is directly proportional to the length.

31
Q

How is the area of a conductor proportional to resistance?

A

The larger the cable diameter the lower the resistance. The cross-sectional area of a conductor is inversely proportional to the resistance.

32
Q

How does the material affect resistance?

A

The higher amount of free electrons of a material type the lower the resistance.

33
Q

What happens to most materials when the temperature is increased?

A

Resistance will also increase.

34
Q

What does temperature coefficient refer to?

A

The amount of increase in resistance for each degree change in temperature.

35
Q

What is a positive temperature coefficient?

A

When resistance of a material increases when the temperature increases.

36
Q

What is the temperature coefficient for copper and aluminum?

A

0.0039

37
Q

What approximate temperature is needed for some materials to become superconducting and have no resistance?

A

-271℃

38
Q

What does each type of material have?

A

A resistivity value which is measured in ohm-metre (Ω*m). This is the resistance in ohms of a cube of material 1m by 1m by 1m.

39
Q

What is resistivity expressed at for the electrical trade?

A

20℃

40
Q

What is the resistivity of copper and aluminum at 20℃?

A

Copper is 1.72 x 10⁻⁸
Aluminum is 2.83 x 10⁻⁸

41
Q

How many gauges of wire are there in the American Wire Gauge system(AWG)?

A

40

42
Q

What is the largest and smallest wire size in the AWG system?

A

36 AWG is the smallest.
4/0 is the largest.

43
Q

What wire sizes are listed in the CE code?

A

No. 14 AWG to 4/0 AWG.

44
Q

What are wires smaller than 14 AWG used for?

A

Mainly appliance and control wiring.

45
Q

What does the wire size number represent?

A

The amount of times the wire was pulled through a die.

46
Q

What can you use to determine a wire size?

A

AWG gauge tool which is 36 AWG to 0 AWG.
Calipers.
Micrometer.

47
Q

What is the formula to solve for area of a circular conductor?

A

π x r²
π is constant
r is radius in mm. (diameter divided by two.)

48
Q

What does cmill stand for?

A

Circular mil

49
Q

What are wires larger than the AWG system described by?

A

Thousand circular mils (kcmil) K stands for kilo. CE code has 250 kcmil to 2000 kcmil.

50
Q

What is a mil?

A

One one thousandths of an inch (1/1000)

51
Q

How much does the resistance and area change every 3 gauge sizes up or down?

A

The area and resistance is approximately doubled or halved every 3 gauge sizes. If area is doubled resistance is halved.

52
Q

How do you determine the approximate area and value of in between AWG wire sizes?

A

Multiply or divide the gauge size by a factor of 1.26. Multiply if going up a wire size and divide if going down for area and reverse for resistance.

53
Q

What is the percentage change in area for each gauge size change in the AWG wire table?

A

26%

54
Q

How small can a single fibre optic cable be?

A

A fraction of a millimetre in diameter.

55
Q

How much more information can a fibre optic cable handle over copper?

A

Hundreds of times more bits of information per mm² of area.

56
Q

Due to fibre optics sending signals as light waves, what are they immune to?

A

Immune to electromagnetic interference and do not generate electrical noise(interference) of their own.

57
Q

Why are fibre optic systems safe to use in an explosive environment?

A

Due to using light signals there are no grounding or voltage problems.

58
Q

What does a fibre optic cable consist of?

A

A number of hair-like glass or plastic optical fibres. Each fibre is individually covered with a cladding material and is isolated from other fibres.

59
Q

What does the cladding material do for the fibre optic cable?

A

Causes the light to reflect inwards towards the core, which prevents the escape of light and signal strength.

60
Q

What safety measures must be taken when handling fibre optic cables?

A

Avoid touching the ends of the fibre to ensure no damage or contamination to the fibres.
Ends may shatter, causing small fragments to be transferred to the skin or eyes.
Never look into the end of a connected cable because the intense light could damage the retina.

61
Q

What are the four common ways fibre cables can be damaged?

A

Crushing
Excessive Tensile Stress
Excessive Bending
Contamination

62
Q

How can crushing occur?

A

When trenches are not carefully backfilled.

63
Q

How can excessive tensile stress be avoided?

A

Use tension fuses which are links that break if the cable is pulled to hard.

64
Q

What is the common amount to leave at an enclosure for proper termination of fibre optic cables?

A

5 Metres.

Pre-Employment Electrician Theory (8 decks)

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