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CORK INSTITUTE OF TECHNOLOGY
INSTITIÚID TEICNEOLAÍOCHTA CHORCAÍ
Semester 2 Examinations 2011/
Module Title: Electrical Installation Practice
Module Code: ELEC
School: Mechanical, Electrical & Process Engineering
Programme Title: Bachelor of Engineering in Electrical Engineering – Year 1 Bachelor of Engineering (Hons) in Electrical Power Systems – Year 1
Programme Code: EELEC_7_Y EEPSY_8_Y
External Examiner(s): Ms Mary Desmond, Mr Colm Murray Internal Examiner(s): Mr Donal Neally
Instructions: Answer SIX questions. All questions carry equal marks.
Duration: 2 hours
Sitting: Summer 2012
Requirements for this examination: ET101 – ETCI Rules
Note to Candidates: Please check the Programme Title and the Module Title to ensure that you have received the correct examination. If in doubt please contact an Invigilator.
Q1. (a) Explain why the conductor shape of large CSA multicore power cables may not necessarily be circular. Illustrate your answer with suitable examples. (6 marks) (b) State the insulation colours of a modern 5 core S.W.A. power cable, indicating what each core is to be used as. (5 marks) (c) Describe the construction of a common steel wire armoured power cable. (6 marks)
Q2. (a) Describe an industrial type overhead bus-bar wiring system. (6 marks) (b) What is the purpose of an expansion joint when fitted to the bus-bar systems? (3 marks) (c) What is the main advantage of supplying power to the bus-bar mid-way in the bus-bar run, relative to supplying the power to one end only of the bus-bar system? (4 marks) (d) Explain why it is required to install circuit-breakers or fuse/switches at every take-off point in an overhead bus-bar system. (4 marks)
Q3. (a) Part of a new installation comprises of a steel trunking to contain the following PVC insulated copper wires:- 72 X 1.5mm^2 30 X 2.5mm^2 9 X 4mm^2 6 X 6mm^2 Determine the minimum acceptable trunking size. (12 marks) (b) A 20mm conduit run is 5m long and contains 2 bends. Determine the maximum number of 2.5mm^2 PVC/CU wires which can be enclosed in this conduit in order to comply with the ETCI rules. (5 marks) Q4. (a) Sketch and describe an NYM-J type cable. (6 marks) (b) What type of gland should be used when terminating the above type of cable? (4 marks) (c) Distinguish between NYM-J and NYM-O versions of this type of cable. (4 marks) (d) State ONE example where NYM-J is frequently used for the fixed wiring of an installation. (3 marks)
Q5. (a) State TWO types of armouring that are used in the manufacturing of power cables. (8 marks) (b) An armoured PVC- insulated multi-core cable with copper conductors is fixed to a wall. It has a voltage drop of 15mV per ampere per meter and the cross sectional area of the cable conductors is 2.5mm^2. Calculate the voltage-drop in a 25 meter run of this cable when it carries a current of 20 amps. (9 marks)
