June 2018 Flashcards
State three documents that should be available to a site electrician during the construction phase
of an electrical installation.
Risk assessment
Method Statement
Design specification
Site plan / building plan
Manufacturer’s instructions / Data sheets
State three types of inductive transformer.
solation / separation
Laminated core
Toroidal
Autotransformer (will accept auto)
Explain why pumped storage electricity generation is used, in preference to traditional fuel sources,
to provide supply flexibility when demand fluctuates.
To include reference to traditional fuel sources
(coal/gas/nuclear etc.) that are slow to start and stop
the generation process (1 mark) whereas water
turbines (1 mark) can be put on and off line rapidly
(1 mark).
Explain why all Live conductors of the same A.C. circuit must enter a steel-cased consumer unit
through one single hole.
As the magnetic fields induced by
each conductor are offset by the opposing fields. If
they are not, then eddy currents induced will create
a heating effect and vibration.
State three gases or metallic vapours commonly used in discharge lamps.
Hydrogen
Helium
Mercury
Sodium
Magnesium
Explain why star-delta motor control equipment is used in preference to direct-on-line
Star configuration reduces the line current during
start-up (1 mark) then delta configuration increases
the torque whilst running (1 mark), whereas directon-line both start and run in delta (1 mark).
Explain the drawbacks of BS 3036 fuses.
Poor fusing factor and cables need to be de-rated (1
mark), as they may over-heat (1 mark)
Fuse wire can be easily replaced with the wrong
size or type (1 mark), which may lead to overheating of the cable, potentially resulting in a fire
and/ or damage to cable (1 mark).
Carriers have poor prospective fault carrying
properties (1 mark) which may explode under fault
conditions (1 mark)
State three factors, given in BS 7671, to be taken into account when calculating the maximum
demand of an installation.
Location of points of power demand
Loads to be expected
Variation of demand (time of consumption)
Special conditions e.g. harmonics
A new passive infra-red occupancy sensor has been installed to control the lighting in a hotel
corridor.
Describe the process of carrying out functional testing of these sensors
Sensors to be adjusted to test settings (1 mark),
they must activate the appropriate lights when
people move in appropriate locations(s) (1 mark)
and must be correctly adjusted for time and light
level (1 mark)
Describe three practical measures that can be taken to ensure the safety of other people, when
carrying out inspection and testing.
Inform people of dangers
Post signs for awareness
Barrier off areas to make people aware/ restrict
access
Provide adequate lighting for safe access/ egress
Ensure lifts unoccupied (before isolation)
Explain why a newly installed gas central heating boiler must be disconnected from a circuit before
an insulation resistance test can be carried out.
Insulation resistance tests require a voltage to be
applied to the circuit (1 mark) which may, if the
boiler is left connected, produce false readings (1
mark) and/ or damage sensitive electronic
components (1 mark).
State three hazardous materials that may require specialist disposal when undertaking fault
rectification work.
Mercury (or items containing e.g. fluorescent lamps)
CFC’s (or items containing e.g. fridges)
Asbestos
Oil
Identify three pieces of verbal information an electrician should seek from a user when undertaking
diagnosis of an intermittent electrical fault.
How long has the fault been occurring
How long does the fault last for
Symptoms of fault
How often does the fault occur
State the upper voltage limits for Extra-Low Voltage.
50 V ac (1 mark)
120 V dc (1 mark)
Explain the effect of running a cable through 200 mm of thermal insulation
The thermal insulation will reduce the ability of the
cable to dissipate heat (1 mark) which will reduce
the current carrying capacity (or damage cable if not
reduced)(1 mark). The correction factor to be
applied to take account of the reduced current
carrying capacity, Ci, is 0.63 (1 mark)
