Section A-
1. What is the maximum number of main switches permitted in a domestic installation?
a) There is no limit
b) 4
c) 2
d) 1
2. Prospective fault current is:
a) the current that will flow when a fault occurs
b) the maximum current that can flow when a fault occurs
c) the hypothetical current that could flow when a fault occurs
d) the minimum fault current that can flow when a fault occurs
3. The tripping current rating of the circuit barker must always
a) Be greater than the cable current rating but less than the load current rating
b) Be greater than the cable current rating and the load current rating
c) Be less than the cable current rating but the load current rating
d) Be less than the cable current rating but greater than the load current rating
4. The nominal tripping current for a circuit breaker is :
a) Equal to the current setting of the circuit breaker
b) 15 times the current setting of the circuit breaker
c) 1.45 times the current setting of the circuit breaker
d) 1.5 times the current setting of the circuit breaker
5. The term "discrimination", when applied to protective devices means:
a) The device closet to the fault will operate first.
b) the device closet to the fault on the load side of the fault will operate first.
c) the device closet to the fault on the supply side of the fault will operate first
d) the smallest current rated device will operate first.
Section B-
Q1. If a circuit breaker is used as an emergency controlling device what factors must it have?
Q2. What is the maximum length a power circuit can be in a domestic installation supplied though a 20A type C circuit breaker so that it needs fault loop impedance requirements?
Q3. How are screw in fuses to be connected?
Q4. AS/NZS 3000 nominates 3 major causes of under voltage. What are they?
Section C-
Q1. A 230V domestic clothes dryer takes 4 hrs to dry a full load of clothes on the highest heat setting. The dryer 9A from the supply on the highest setting and is normally used week nights from 8pm. Using the table below, how much will it cost to the nearest cent to try this load of clothes?
Q2. What are three examples of circuits that do not require overcurrent protection due to the opening of the circuit causing greater danger that the over current?
Q3. Is it necessary to install RCD protection on an endsting circuit where a angle 10A socket outlet is replaced with a double 10 A socket if the existing circuit does not have RCD protection?
Q4. How are the terminals of switchboard equipments to be marked?
Q5. When selecting the circuit rating if an RCD what requirements must be met?
Q6. Which of the following provides fault current protections?
a) HRC fuse
b) BCD
C) Switch
Q7. The thermal component if a thermal magnetic circuit breaker operates by
a) Installation tripping in short circuit
b) Thermal ERP
c) having a by metal strip
d) a proportional responsive curve
Q8. Under voltage can be caused by
a) A break in the MEM.
b) High impedance in the supply conductors
c) Increasing the of the consumers mains
d) Lending lights on overnight
Q9. Under voltage protections is commonly used on?
a) domestic installation
b) safely service
c) Industrial lighting
d) Motor circuits
Q10. The normal operating current for an ACD in general and specialized use are:
a) 100 mA and 30 mA respectively
b) 30 mA and 10mA respectively
c) 100mA and 10mA respectively
d) 10mA and 30mA respectively
Q11. The consumer's mains, to a single phase installation are 35 mm2 copper conductors. Determine the size of the main carting conductors
a) 6 mm2
b) 10mm2
c) 25 mm2
d) 35 mm2
Q12. In reference to an electrical installation the term ‘MEN' stands for
a) Multiple Earthed Neutral
b) Main Earthed Negative
c) Multiple Earthed Negative
d) Main Earthed Negative
Q13. The fault loop impedance is generally considered to be:
a) Equal to the determined impedance of the active and neutral cables
b) Equal to the measured resistance of the active and neutral cables
c) Equal to the determined impedance of the active and earth cables
d) Equal to the measured resistance of the active and neutral cables
Q14. When deterring the maximum length of the circuit to satisfy the requirement for fault loop impedance the supply voltage is
a) 50 % of the nominal value
b) 60 % of the nominal value
c) 80 % of the nominal value
d) 100 % of the nominal value
Q15. What is the maximum value of touch voltage allowed
a) 50 V ac
b) 120v ac
s) 10mA
d) 230V ac
Q16. Indirect contact can best be described when:
a) The covers are removed from a switchboard and the uninsulated busbars are short circulated
b) Bare conductors are accidentally short circuited
c) A child puts a knife in a socket outlet
d) The exposed conductive parts become live due to a breakdown of insulation within.
Q17. Accordance to AS3000 what are the limits of arms reach
Q18. Why it is necessary that every electrical installation shall be divided into multiple circuits?
Q19. Provide the minimum size of Equipotential bonding conductors for the following situations:
a) Metallic water piping _________
b) Metallic-fire sprinkler, gas or flammable liquid pipes _________
c) Metallic cable sheaths and wiring enclosures in contact with pipes containing flammable liquids or gases _________
d) Metallic parts of swimming and spa pools _________
e) Telecommunications earthing systems _________
f) Metallic enclosures and supports associated with unprotected consumer's mains _________
Section D -
Q1. Determine the maximum value of the fault loop impedance for a 230 V circuit that is protected by 20 A type ‘C' Circuit breaker.
Q2. A cable has a current carrying capacity of 20 Amps when protected by a 20 Amp circuit breaker. Determine the current carrying capacity for this same cable it protected by a HRC fuse.
Q3. If the maximum demand of a sub-main was determined to be 155 A, Use table 2 and the fault levels indicated below to select a suitable protective device for the sub-main.
Fault level at point of supply: 30kA
Fault level at main switchboard : 24 kA
Fault level at switchboard : 18 kA
Designation of selected device :
Q4. Determine the current value required for a 80 amp HRC fuse to operate in .4 seconds.
Q5. A 32amp fuse is subjected to an overload of 80a, determine time it takes to operate.
Drawing graphical question
Q show the required to
Q6. A 40A type ‘C' CB is subjected to an overload of 80A. Using the appropriate curve in figure 2, determine the time range it will take to operate.
Q7. What factors will be considered when determining the sustainability of switchboard?
Q8. The Co-ordination between conductors and protectors devices requires that two conditions must be satisfied for the operating characteristics of a device protecting a conductor against overload. They are?
Q9. As for low voltage for the supply to be legal the nominated value must not drop lower than what value, when load is applied to the circuit?
Q10. AS/NZS 3000 nominates 4-major causes of over voltage. What are they?
Q11. What us requirements shall be taken into account when deciding the location of a switchboard?
Q12. According to ASNZS 3000 an overcurrent device and overcurrent protection define is there to ensure against what?
Q13. Where consumers mains are not protected on the supply side by short circuit protective devices, the MEN link shall have a cross sectional area not less than that of the?
Q14. What are the requirements of fixed electrical equipment that could attain surface temperatures that would cause a fire hazard to adjacent materials?
Q15. A block of 3 units has 3 meter, 1 per unit and an meter for lighting. How many main switches will be located on the switchboard?
a) 1
b) 5
c) 4
d) 3
Q16. The voltage drop is an voltage extra low voltage installation shall not exceed what %
a) 8
b) 9
c) 5
d) 10
Q17. Which of the following considerations is not necessary in determining the number and type of circuit within an electrical installation?
a) Load on the various circuits
b) location of the points or load
c) Exposure to external installation
d) Seasonal and daily variation of demand
Q18. The switch used isolate a 12.5 kw range (cook top) that is connected to two phase and neutral would have as a minimum:
a) One pole
b) Two poles
c) Three poles
d) Four poles
Assignment Files -
https://www.dropbox.com/s/9jxr97umomcahn1/Assignment.rar?dl=0