Maximum Demand and Cable Selection

Question 1

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

Answer 1

5%

Question 2

What produces voltage drop?

Answer 2

Load current and impedance of the circuit conductors

Question 3

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

Answer 3

Heat

Question 4

Heat is proportional to the _____ of the _____.

Answer 4

Square, Current

Question 5

Torque is proportional to the _____ of the _____.

Answer 5

Square, Voltage

Question 6

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

Answer 6

The stator

Question 7

Power is proportional to the square of the _____ _____.

Answer 7

Supply voltage

Question 8

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

Answer 8

Series

Question 9

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

Answer 9

11.5 V

Question 10

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

Answer 10

20 V

Question 11

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

Answer 11

Table C8

Question 12

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

Answer 12

Maximum demand of the portion it supplies.

Question 13

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

Answer 13

0.9

Question 14

Formula for V(c)

Answer 14

1000 x V(d) / L x I

Question 15

Formula for V(d)

Answer 15

L x I x V(c) \ 1000

Question 16

What is a characteristic of XLPE?

Answer 16

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

Question 17

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

Answer 17

Table C1

Question 18

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

Answer 18

Table C2

Question 19

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

Answer 19

Table C5

Question 20

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

Answer 20

Table C2

Question 21

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

Answer 21

8.1, fault-loop impedance, secondary

Question 22

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

Answer 22

False. Must also meet max volt drop limits.

Question 23

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.

Answer 23

Diversity factor

Question 24

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

Answer 24

0.866

Question 25

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?

Answer 25

1.155

Question 26

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

Answer 26

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

Question 27

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

Answer 27

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

Question 28

What does coordination between conductors and protective devices ensure?

Answer 28

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

Question 29

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

Answer 29

6 kA

Question 30

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

Answer 30

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

Question 31

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

Answer 31

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

Question 32

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

Answer 32

Partially surrounded by insulation.

Question 33

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

Answer 33

Category A

Question 34

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

Answer 34

A, except when chased into brick with no enclosure.

Question 35

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

Answer 35

Table 3.6

Question 36

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

Answer 36

Table 3.5

Question 37

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

Answer 37

Section B.5

Question 38

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

Answer 38

B1 and B2

Question 39

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

Answer 39

Section B4.5

Question 40

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

Answer 40

4 x rated current

Question 41

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

Answer 41

7.5 x rated current

Question 42

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

Answer 42

12.5 x rated current

Question 43

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?

Answer 43

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

Question 44

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

Answer 44

Limiting temperatures per Table 1.

Question 45

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

Answer 45

Table 3 (1-4)

Question 46

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

Answer 46

Table 4 - 21

Question 47

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

Answer 47

Tables 22 - 26

Question 48

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

Answer 48

26 (1 - 2)

Question 49

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

Answer 49

Section 4 of the AS/NZS 3008

Question 50

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

Answer 50

Tables 52 and 53

Question 51

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

Answer 51

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

Question 52

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

Answer 52

False

Question 53

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?

Answer 53

False

Question 54

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

Answer 54

Table B1

Question 55

What is %Z?

Answer 55

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