Questions

Question 1

List two methods of charging secondary cells

Answer 1

•Trickle charging
•Constant current
•Constant voltage
•float charging

Question 2

Describe 2 quarterly test requirements of a self contained em system

Answer 2

•Functional test (3 hour system) 3 hour test
•visually check emergency luminaires and exit signs

Question 3

Describe a combined sustained emergency lamp

Answer 3

Contains at least 2 lamps one of which is energised from the normal light supply, other lamp is supplied by em supply, light is intended to be alight at all times

Question 4

Compare sox lamp with high pressure mercury MBF

Answer 4

Sox- colour rendering very poor
Efficacy up to 200 lm/w
Run up time 8-12 mins

MBF
Colour rendering fair produces bluish white colour
Efficacy 35/55 Lumen per watt
Run up time 4-5 mins

Question 5

Four precautions when connecting aluminium cables to copper busbar

Answer 5

•use bi-metallic lugs (UI-CU) compression lugs
•keep connections clean
•keep the connection dry
Ensure busbar is not live

Question 6

Flexible motors are used on electric motors, state function and how motor is aligned

Answer 6

•Function is to mechanically connect a motor to a load
•alignment can be done by using a straight edge or steel rule, motor base can be adjusted by placing packing pieces under the motor

Question 7

Describe the construction of STP cable used in cat6

Answer 7

•has 4 twisted pairs of insulated copper
•each pair is twisted together
•overall twist between pairs
•metallic sheet/foil wrapped around all pairs
•overall outer sheath/jacket

Question 8

Compare copper to aluminium under mechanism properties

Answer 8

Aluminium
•cheaper in cost/ less in demand
•Three times lighter in weight/ easier to handle
•61% less conductive as copper 16mm copper same as 25mm alum

Copper
More expensive
Higher current carrying capacity
Better conductivity rate than aluminium

Question 9

Describe what the electrolytic effect between copper and aluminium

Answer 9

If an electrically conductive liquid such as condensation reaches an aluminium and copper connection an electrochemical reaction occurs and causes contact element formation

Question 10

Explain HBC fuse

Answer 10

The high breaking capacity fuse can deal safely with very high fault currents, often used in industrial circuits with high fault currents

Question 11

List four advantages of XLPE over PVC

Answer 11

•XLPE has a higher running temp 90 degrees vs PVC 70 degree
•XLPE much tougher construction
•XLPE is oil and solvent resistant PVC isn’t
•XLPE used as insulation for power distribution larger power cables

Question 12

Describe construction of a UTP cable

Answer 12

•four twisted pairs
•enclosed in a protective plastic cover
•each set of twisted pairs are twisted altogether
•all twisted pairs are enclosed in a foil wrapping

Question 13

Linear vs switch mode power supply

Answer 13

A linear power supply steps down the AC voltage first then converts it into DC while the switch mode converts AC to DC and then uses a step down transformer to obtain the desired voltage

Question 14

Linear power supply uses

Answer 14

•Ups system
•intruder alarm panel power supply
•high freq power supply

Question 15

Switch mode power supply uses

Answer 15

•mobile phone chargers
•led light controllers

Question 16

State four devices used to protect motors from overload

Answer 16

•MCB
•Thermal overload
•Thermistor relay
•Fuse

Question 17

Star tropology

Answer 17

Each data point is wired with a singular dedicated cable back to a central hub eg RJ45 points wired back to switch panel

Question 18

Bus tropology

Answer 18

Cable is in a loop in and out arrangement for each device (DALI system 2 cores looped between fittings)

Question 19

State one advantage a three-phase bridge rectifier has compared to a single phase one

Answer 19

Improved output voltage as the ripple output voltage is reduced considerably compared to to a single phase, this reduces the capacitive filtering required to reduce the ripple voltage

Question 20

State one application for three phase rectifier

Answer 20

•Commercial electric car charging stations
•large uninterrupted power supplies

Question 21

Name two methods of coupling motor to load

Answer 21

•Solid coupling
•Flexible coupling

Question 22

State one advantage a double cage induction motor has over a single cage motor

Answer 22

•improved starting torque
•improved running efficiency

Question 23

Self contained emergency lighting

Answer 23

Includes a lamp battery, charger and detecting device for detecting the presence of normal supply, all contained in one unit must be within one metre from the luminaire
Advantages:
•Low cost install doesn’t require fire cable
•each unit works independently
•no maintenance apart from periodic functional tests

Question 24

Escape lighting

Answer 24

•clearly identify the escape routes
•provide illumination along routes towards exits
•ensure fire alarm call points and fire equipment is clearly visible

Question 25

Central battery system

Answer 25

Central battery in a well ventilated battery room, own battery charger, control system, requires fire tuff cables

Question 26

Combined and sustained

Answer 26

Atleast 2 lamps one is energised from normal supply and other from emergency supply, one lamp intended to light at all times

Question 27

Non maintained

Answer 27

Emergency light lamp are in operation only when the supply to the normal lighting fails

Question 28

When do you have maximum torque

Answer 28

When the resistance and reactance in the rotor is equal