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RMIT University – School of Engineering/ Electrical and Biomedical Engineering EEET2384/ 2385- Introduction to Electrical Building Design Sample Mid Semester Test

45 minutes

Name:…………………………………………

Student ID:…………….………..…..

Question 1: Short-Answer Questions 1. Briefly explain characteristics of two equipment classes outlined in AS3000. (2 Marks)

2. State three disadvantages of Fuses over MCBs. (3 Marks)

3. Briefly explain the characteristics of three types of MCBs. (3 Marks)

4. List two advantages of LED globes over incandescent globes. (2 Marks)

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Question 2: Maximum Demand and Voltage Drop Calculations An apartment unit comprises dining, kitchen, 2 bedrooms, bathroom, with the following load specification: a) 3 off lighting points per major room, 2 off per bathroom b) 4 m lighting track in dining room c) 2 off double power points in each major room, 1 per bathroom d) 2 off exhaust fans (bathroom plus kitchen) e) Electric cooking range comprising 2500 W hotplates and 4000 W oven f) 4000 W reverse cycle air conditioning unit g) 2500 W washing machine Assume Single-phase supply for the apartment. 1.

Calculate the Maximum Demand for the Entire Installation. (8 Marks) Load Name

Load Group

Workings

Maximum Demand (A)

1 2 3 4 5 Maximum Demand 2.

Identify the circuit specification (circuit load, load types, cable size and protective device rating) for the above loads and complete the Table 2. (14 Marks) Table 2: Circuit Specification for the Apartment Unit Load Group

Circuit Name

Maximum Demand (A)

Cable Size (mm2)

Protective Device Rating (A)

1

2 3 4

5 6 7

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3. If the 4000 W reverse cycle air-condition unit and 2500 W washing machine located at 12 m and 8 m respectively from the main switchboard calculate the voltage drop for each circuit. (4 Marks)

Question 3: Protection Coordination 1.

A schematic of a three-phase 415 V/50 Hz electrical installation is shown in Fig. 1. Assume all loads are balanced three-phase loads.

▪ Lighting load: Comprised of florescent light globes operating at 0.85 pf and instantaneous starting current is 4 times the normal steadystate current. ▪ Motor load: Motor efficiency is 95% and operating at 0.80 pf, starting current is 9 times the steady-state current and it will last for 10 seconds. 10 kW Lighting Load

20 kW Motor

Calculate the following: (i) Steady-state current for each load. (4 Marks)

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(ii) If the fuses are to be employed for each load as the protection mechanism chose appropriate rating for the fuses for each load? (3 marks)

(iii) What should be the rating of the fuse located at point A. (3 marks)

2. Determine the maximum route length for a circuit which has Type C circuit breaker rated at 20 A. Assume Active and Earth conductors are sized at 2.5 mm2. (4 marks)

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Useful Formulas V = (L x I x VC) /1000 d

%Vd

= (100/Vo) X (L X I X VC) /1000

I2 t = K2 S2

IB < IN < IZ

I2 < 1.45IZ IB < IN < 0.9IZ

Zs = Zext + Zint Zs = Uo/Ia

Zint = 0.8 Uo / Ia

Lmax 

0.8U 0 S phS pe I a  ( S ph  S pe )

S  ( I 2t / K 2 )

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Fuse Characteristic Curves

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NOTES TO TABLE C1: a

b

c

d

See Clause 2.2.2 for where the maximum demand for consumers mains, and submains, and final subcircuits, respectively, may be determined by assessment, measurement or limitation. For multiphase connections, divide the number of living units by the number of supply phases, e.g. 16 units on a three-phase supply, 16/3 = 6 units on the heaviest loaded phase (Column 4). Where only a portion of the number of units in a multiple domestic electrical installation is equipped with permanently connected or fixed appliances, such as electric cooking ranges or space heating equipment, the number of appliances in each category is divided over the number of phases, and the maximum demand determined as shown in Example 3 of Paragraph C2.3.2. Lighting track systems shall be regarded as two points per metre of track.

e

A socket-outlet installed more than 2.3 m above a floor for the connection of a luminaire may be included as a lighting point in load group A(i). An appliance rated at not more than 150 W, which is permanently connected, or connected by means of a socket-outlet installed more than 2.3 m above a floor, may be included as a lighting point in load group A(i). f In the calculation of the connected load, the following ratings shall be assigned to lighting: (i) Incandescent lamps 60 W or the actual wattage of the lamp to be installed, whichever is the greater, except that if the design of the luminaire associated with the lampholder permits only lamps of less than 60 W to be inserted in any lampholder, the connected load of that lampholder shall be the wattage of the highest rated lamp that may be accommodated. For multi-lamp luminaires, the load for each lampholder shall be assessed on the above basis. (ii) Fluorescent and other discharge lamps Full connected load, i.e. the actual current consumed by the lighting arrangement, including the losses of auxiliary equipment, such as ballasts and capacitors. (iii) Lighting tracks (230 V) 0.5 A/m per phase of track or the actual connected load, whichever is the greater. g Floodlighting, swimming pool lighting, tennis court lighting and the like. h For the purpose of determining maximum demand, a multiple combination socket-outlet shall be regarded as the same number of points as the number of integral socket-outlets in the combination. i Each item of permanently connected electrical equipment not exceeding 10 A may be included in load group B(i) as an additional point. j Where an electrical installation contains 15 A or 20 A socket-outlets covered by load group B(ii) or B(iii), the base loading of load group B is increased by 10 A or 15 A respectively. If both 15 A and 20 A socket-outlets are installed, the increase is 15 A. k Where an electrical installation includes an air-conditioning system for use in hot weather and a heating system for use in cool weather, only the system that has the greater load shall be taken into account. l Instantaneous water heaters including ‘quick recovery’ heaters having element ratings greater than 100 W/L. m Storage-type water heaters, including ‘quick recovery’ heaters not referred to in footnote l. n This load group is not applicable to socket-outlets installed in communal areas but connected to the individual living units. Such socket-outlets should be included in load group B.

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