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Australian Context Gap Training > Maximum Demand and Cable Selection > Flashcards

Maximum Demand and Cable Selection Flashcards

1
Q

According to AS/NZS 3000 what is the maximum allowable voltage drop from Point Of Supply to any point in the installation?

A

5%

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2
Q

What produces voltage drop?

A

Load current and impedance of the circuit conductors

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3
Q

The most significant factor to choosing cables for an installation is _____.

A

Heat

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4
Q

Heat is proportional to the _____ of the _____.

A

Square, Current

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5
Q

Torque is proportional to the _____ of the _____.

A

Square, Voltage

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6
Q

Which part of an induction motor will overheat due to too low of voltage?

A

The stator

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7
Q

Power is proportional to the square of the _____ _____.

A

Supply voltage

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8
Q

Voltage drop for any installation is the sum of each _____ connected circuit cable from Point Of Supply to the Load.

A

Series

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9
Q

What is the maximum voltage drop for a 230V system?

A

11.5 V

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10
Q

What is the maximum voltage drop for a 400V system?

A

20 V

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11
Q

When circuit length and current are known, what is the simplified method to calculation voltage drop according to AS/NZS 3000?

A

Table C8

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12
Q

The size of conductor for each submain phase must be rated to carry what?

A

Maximum demand of the portion it supplies.

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13
Q

When a submain is protected by HRC fuse, what is the derating factor?

A

0.9

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14
Q

Formula for V(c)

A

1000 x V(d) / L x I

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15
Q

Formula for V(d)

A

L x I x V(c) \ 1000

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16
Q

What is a characteristic of XLPE?

A

Will hold it’s shape & and not ‘flow’ under mechanical stress.

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17
Q

Which table in the AS/NZS 3000 is used to calculate maximum demand for a domestic installation?

A

Table C1

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18
Q

Which table in the AS/NZS 3000 is used to calculate maximum demand for a hospital?

A

Table C2

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19
Q

Simplified maximum demand for cooking appliances can be found in _____ of the AS/NZS 3000

A

Table C5

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20
Q

What table would be used to calculate maximum demand for a retail shop?

A

Table C2

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21
Q

Table ___ of the AS/NZS 3000 gives maximum values of earth _____ _____, including up to the _____ of the supply transformer.

A

8.1, fault-loop impedance, secondary

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22
Q

The current-carrying capacity of a conductor is sufficient enough information when selecting a cable - True or False?

A

False. Must also meet max volt drop limits.

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23
Q

What takes into account the normal operating conditions of circuits during which all equipment is not operating simultaneously at full load or for periods exceeding 15 minutes.

A

Diversity factor

24
Q

When calculating maximum demand for a single phase installation, what multiplier is to be used to convert to a 3 phase value?

A

0.866

25
Q

When calculating maximum demand for a single phase installation, what multiplier is to be used to convert from a 3 phase value back to single phase?

A

1.155

26
Q

What are four external influences to consider when selecting electrical equipment for a system?

A

1 - Ambient temperature
2 - Heat sources
3 - Water and humidity
4 - Solid foreign bodies

27
Q

What four factors affect the current-carrying capacity of a cable?

A

1 - Type of conductor
2 - Types of cables
3 - Conditions of installation
4 - External influences

28
Q

What does coordination between conductors and protective devices ensure?

A

Safe Working Limit.

Ensures protective device will operate correctly before damage occurs to equipment and cables in a fault.

29
Q

What is the minimum fault current rating of switch gear at the main switchboard of an electrical installation?

A

6 kA

30
Q

How does a voltage drop calculation differ in the case of a Distributed Load power circuit?

A

The current value used may be 50% of the circuit breaker rating instead of the full circuit demand.

31
Q

Three examples of types of circuit groups in an electrical installation are…

A

1 - Lighting, power
2 - Mechanical services
3 - Safety services

32
Q

In a domestic installation, it should be assumed that unenclosed cables clipped to a ceiling joist will be _____________.

A

Partially surrounded by insulation.

33
Q

A cable suitable to be buried without the protection of an enclosure or other mechanical protection is part of a _____ __ wiring system.

A

Category A

34
Q

SWA cable is classified as a Category __ wiring system except when?

A

A, except when chased into brick with no enclosure.

35
Q

Which table in the AS/NZS 3000 is used to select the minimum depth cover for a Category B wiring system?

A

Table 3.6

36
Q

What table can be used to determine which category wiring system a type of cable will be classified?

A

Table 3.5

37
Q

Maximum route length of a circuit can be calculated using the steps outlined in which part of the AS/NZS 3000?

A

Section B.5

38
Q

Two useful tables to determine maximum route length of circuits are __ and __.

A

B1 and B2

39
Q

When calculating earth fault-loop impedance, use this section of the AS/NZS 3000…

A

Section B4.5

40
Q

What is the mean tripping current of a Type B circuit breaker?

A

4 x rated current

41
Q

What is the mean tripping current of a Type C circuit breaker?

A

7.5 x rated current

42
Q

What is the mean tripping current of a Type D circuit breaker?

A

12.5 x rated current

43
Q

In addition to confirming I(b) < I(n) < I(z), what multipliers are used with I(z) to ensure effective operation of the selected protective device?

A

1.45 for circuit breakers. 1.6 for fuses. Per B3.2.

44
Q

What is the first step using the AS/NZS 3008 when determining cable size for an electrical installation?

A

Limiting temperatures per Table 1.

45
Q

Which tables of the AS/NZS 3008 are used to determine method of installation?

A

Table 3 (1-4)

46
Q

Which tables of the AS/NZS 3008 are used to determine current-carrying capacities of cables?

A

Table 4 - 21

47
Q

Derating factors for circuits is determined using which part of the AS/NZS 3008?

A

Tables 22 - 26

48
Q

The derating factors for underground submains would be determined using which table in the AS/NZS 3008?

A

26 (1 - 2)

49
Q

For different methods of voltage drop calculations, which section of which standard should be referenced?

A

Section 4 of the AS/NZS 3008

50
Q

Which tables in the AS/NZS 3008 are used to determine calculated permissible short-circuit current?

A

Tables 52 and 53

51
Q

When using a circuit breaker or fuse size for cable selection, how must you determine the selection?

A

Apply relevant de-rating factors to the circuit and find the nearest > cable size that meets this calculated rating.

52
Q

When using a calculated current rating to select a cable size, the calculation is the CCC - True or False?

A

False

53
Q

If you have a 32A CB and de-rating factors produce a 48A requirement for CCC, a 45A rated cable will be acceptable since the circuit is only 32A anyway - True or False?

A

False

54
Q

How can you determine max cable length when you know the size and type of circuit breaker and size of cable?

A

Table B1

55
Q

What is %Z?

A

Percentage of primary voltage required for full load secondary current to flow in shorted secondary winding

Australian Context Gap Training (11 decks)

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