Tuesday 12 July 2011

2391 concern about past exams




These notes have been compiled while the 16th edition was in place. They are from the
exam bodies notes and pick up on the areas in which the students sitting the exam are
making the most errors. The introduction of the 17th edition has changed some of the
terms used. Please take these into consideration before the examination.
Use of correct terminology
Correct terminology must be used as detailed in BS 7671 and Guidance Note Three
(GN3), must be used when answering questions . Students out-dated terms, and incorrect
terminology. For example:
the use of “live” instead of phase (phase in the 17th edition is referred to as line conductor)
“Completion Certificate” in place of Electrical Installation Certificate
The use of incorrect terms to describe the Earthing Conductor and Main Equipotential
Bonding Conductors and to identify protective conductors connected to the MET(main
earthing terminal), were typical errors.
The testing of an ‘open loop’ was often used when describing how to establish R1 + R2
which could imply the circuit is incomplete
Students referred to ‘a schedule of tests’ rather than the Schedule of Test Results.
Basic knowledge
Some Students were unable to state the need for an Electrical Installation Certificate and
very few were able to identify who is responsible for comparing test results and why.
Understanding this is a fundamental requirement for someone who is studying in this
subject area.
It appears that Students have forgotten that 1 MΩ is the minimum acceptable value of
insulation resistance for a circuit and appear to have adopted 2 MΩ as the new value.
Students often lost marks by listing the test sequence for each circuit rather
than the functional tests required, for example, operating the switches on a lighting circuit.
Naming documentation
When stating the required documentation to be completed during an initial verification of
new work, Students often omitted the Schedule of Inspections and the Schedule
of Test Results. Wrong terminology was also common with the “Schedule of Items
Inspected” and a “Schedule of Tests” being wrongly used but common alternatives.
This is also true when a Periodic Inspection Report was required. Students were unable to
identify those statutory documents which are Acts and those which are Regulations For
example, the Electricity at Work Regulations (EAWR) is not an ACT it is a regulation.

In the answers to questions relating to documentation, Students often referred to
documents that do not exist. For example, there is no ‘schedule of tests’ or a ‘Periodic
Inspection and test certificate.’
Completing documentation
The ability of Students to complete standard documents continues to be poor. Much of the
information required to be entered on documents was often omitted. It would appear from
the attempts by some students that they were not familiar with these standard forms.
One question required a Schedule of Test Results to be completed for the two new ring
circuits.
Some responses included a lighting circuit while others gave no information relating to the
circuit conductors.
Another error involved entering the maximum values of Zs in column 12. No functional
tests recorded, no indication that the continuity of ring final circuit test had been completed
successfully and the lack of recording the type of supply and values of Ze and PFC were
other common errors.
Describing test procedures
When describing how to carry out a test, students were often confused as to what was
required, were unable to describe a logical approach and rarely used large clear diagrams
to assist with their description, even when the question requested this.
Practice of these skills during their course would greatly improve the quality of their
answers.
A significant number of answers included dangerous procedures and the use of
inappropriate instruments which, if applied, could have resulted in serious injury.
Answers of a dangerous nature result in no marks being awarded, So remember
permission to isolate, inspect no risk to people property or livestock isolate, lock off, verify
isolation and always select and state the name of the correct meter and in some
circumstances the standard the meter/ leads have to follow (GS38).
Students often forget to seek permission to isolate, and indeed many do not even
mention isolation. Other areas often neglected in answers are the use of GS 38 test leads,
placing links if required, actually connecting the test instrument, recording results and
reinstating the circuit on completion. A large majority of Students stated that the test button
on an RCD is the essential test that must precede the testing of an RCD. This is not the
procedure given in Guidance Note 3. This needs to be explained to Students.

Test values
Many Students were unable to identify correct test values, acceptable test results and the
actual test current to be applied for RCD testing.
One question asked for appropriate scales for given tests. Many Students did not
differentiate between the scale values for earth electrode resistance and continuity of
protective conductors (both given as Ohms).
Where scale values are requested the responses should indicate suitable scales, for The
Question above should have been answered with values of 200 Ω and either low ohms or
>2 Ω would be appropriate.
Calculations
Many Students had problems with calculations related to the inspection and testing
process.
Cumulative IR, resistors in parallel calculations
Calculation of R1 andR2 when given values for Zs and Ze.
These were related to the typical calculations which may be required during the verification
of test results. As these are fundamental to the activities of initial verification and periodic
reporting such calculations should be within the capabilities of the Students.
Exam technique
Students should spend one minute on an answer for each possible mark to be awarded.
For example, a three mark question should take approximately three minutes
to complete, although many questions in Section A will take considerably less than this.
Many Students still use paragraph text to describe procedures rather than use bullet
points. The bullet point approach saves Students’ time and will help them to review their
answers for accuracy.
Careful reading of the question is important. Too many answers did not include the
requested information. For example, the answer to one question required a list of the first
four tests, including instruments, to be carried out on a lighting circuit and two ring circuits.
Often no instruments were quoted and in some cases Students merely reproduced the
standard list of tests in its entirety.
Many Students did not answer the questions in Section B of the paper in relation to the
given scenario and this often resulted in the loss of marks. Students must read the
information carefully and use this in conjunction with the information given in the question.
It may be helpful if students were encouraged to highlight key information in the scenario
as they read it, so that they will become more aware of this as they attempt the questions
in this section.

Question 1 required the student to identify the three types of work for which an EIC would
be issued ‘as identified on the Electrical Installation Certificate’. The majority of Students
identified three forms of certification (EIC, MEWC and PIR) not the three types of
installation work identified on the EIC. New installation, Addition to an existing installation
and alteration to an existing installation.
Question 2 required the student to describe the process for testing continuity of ring final
circuits. Very many Students were unable to describe the process of ring circuit continuity
testing. Many failed to carry out both stage 2 and stage 3, were unable to detail what
information was obtained and expected values. Very few provided drawings as requested.
Question 3 required the student to describe the correct procedure for carrying out an
insulation resistance test on car park lighting columns. Students were generally unable to
correctly describe the testing process with the isolation of columns and testing distribution
cables and then connecting P&N and testing between P&N to E for the columns. Few
Students were able to provide reasons for the use of larger cables than those required to
meet the current carrying requirements.
Question 4 required Students to identify the tests which would need to be carried out
during a one hour period, the only time when the whole installation could be isolated. Most
Students reproduced the sequence of test without any consideration for the situation.
Indeed most Students, judging by their responses, would carry out the complete periodic
inspection and test of the visitor centre in one hour.
Question 5
a) required Students to provide diagrams of the MET (main earthing terminal) with all
associated protective conductors
In the response many Students did not correctly identify all the items which required main
equipotential bonding conductors and failed to correctly identify those conductors which
they did show.
b) a fully labelled earth fault loop path for the 1st car park light.
In the responses to b) many failed to show the correct system. Of those who did produce a
TT system many failed to correctly identify the relevant component parts, earthing
conductor, general mass of earth, MET, R1 and R2 etc.
Question 6 required Students to list, in the correct sequence, the first three tests to be
carried out on a newly installed lighting circuit. Many Students were unable to do so. The
correct titles were not given, the wrong order was stated and including a ring final circuit
continuity test in the sequence were typical errors.

Question 7 requested the identification of three special locations as identified in Part 6 of
BS 7671 in the 16th edition part 7 in the 17th edition , in addition to bathrooms, shower
rooms, saunas and swimming pools. A surprising number of Students were unable to give
three suitable answers. Many gave inappropriate installations identified in Part P of the
Building Regulations while others named installations at random such as petrol stations.
Question 8 required the student to state why the rule of thumb is applied when assessing
the earth loop impedance test result of a circuit. Many Students were unable to offer a
suitable explanation, often stating that it was easier than using more detailed calculations
or “because of temperature”.
Question 9 gave three insulation resistance test results and the student was requested to
identify the circuit condition revealed. Surprisingly, some students stated that 0.00 MΩ
indicated an open circuit.
Question 10 required Students to determine whether measured values of earth loop
impedance for a number of circuits were acceptable. Many answers applied the “rule of
thumb” to the measured values and not to those given in BS 7671. Details of the
necessary calculations were often omitted even though the question requested Students to
show all calculations.
Question 11 of the paper required the student to describe the correct procedure for
carrying out an insulation resistance test on a lighting circuit. Many Students did not state
the instrument to be used, the test voltage and the acceptable test value. Often key
procedural information was not included, operation of two-way switches and disconnection
of loads being typical examples.
Question 12 required the student to describe the process for testing external earth loop
impedance. Some answers stated that it was a live test and then stated the phase (now
line conductor) and cpc were to be connected together. Other answers included the
removal of the earthing conductor while all circuits were energised. Many did not specify
the use of leads to GS 38 and the disconnected earthing conductor was often not
reconnected.
Question 13 required the student to describe the correct procedure for carrying out an
RCD test. Once again guidance was given in the question to help Students include all
relevant details. Often Students did not state the exact test current values, even though
this was clearly requested.
Question 14 asked ‘who is responsible…’ Students saw the word ‘responsible’ and started
referring to the ‘duty holder’ or ‘competent person’. Although the person should be
competent and may well be the duty holder, the student was expected to identify that it
was the person carrying out the inspection.

Question 15 asked Students for the reason why periodic inspections and tests are carried
out in accordance with BS 7671. Few Students stated that it was to determine if the
installation was safe to stay in service. Most decided the question was asking for a list of
reasons or circumstances such as ’the time is due’ or ‘insurance purposes.’
Question 16 required the Students to provide information regarding GS 38 and clearly
stated ‘in addition to items relating to leads and probes.’ Students saw GS 38 in the
question and answered with ‘4mm or fused probes etc.’ Students did not answer the
question asked of them.
Question 17 had the word ‘polarity’ in it. Many Students used ‘ES lamp holders’ and the
like as answers. The question was not asking for examples but the reasons for a polarity
test.
Question 18 asked for a list of tests required, including the instrument and instrument
range in each case. A large majority of Students did not include the ranges required,
resulting in valuable marks being dropped.
Question 19 required Students to identify the instrument and unit of measurement used
when carrying out a test of continuity of protective conductors which many Students
correctly identified.
A large number of Students were unable to state why the particular instrument was used
as required. Typical common errors were that the instrument did not produce a high
voltage, so no risk of shock, or that the instrument would not damage equipment.
Question 20 required Students to state, using the correct terminology, three protective
conductors connected to the main earthing terminal. A large number of Students used
incorrect terminology and common errors included supplementary bonding, lightning
conductors, main earth bonding and earthing to services.
Question 21 related to the reasons for the ring final circuit continuity test. Many Students
were unable to identify the reasons for the test and so were unable to demonstrate their
understanding of the need for the process. A large number of Students identified the
recording of R1 + R2 and/or Polarity neither of which are the reason for the test but are
actually obtained as a consequence of the test.
Question 22 - Very few Students were able to correctly identify the use of the X in the IP
code references, far too many believed that there was no protection offered for the
particular protection item. A surprising number still do not appreciate the significance of the
code in regards to the level of protection is offered.
Question 23 - Many Students were unable to state two methods of confirming compliance
of measured Zs with the requirements of BS 7671. Common responses included,
calculation, measurement, multiply by 0.75 (but not what was multiplied) and enquiry.

Question 24 - Many Students confused prospective fault current with prospective earth
fault current. Consequently their answers were not correct as they would test for pfc and
pscc then record pfc on the certificate.
Question 25 - A large number of Students, in fact far too many, responded that the
measurement of pfc was related to the disconnection time of the device. Too few identified
the relationship to max fault current rating of protective devices.
Question 26 - Many Students incorrectly stated that the inspector was responsible for
determining the period to the first periodic inspection.
Question 27 - Many Students stated that the core of the swa could not be used as a main
equipotential bonding conductor giving reasons such as it was not continuous, not
connected at the MET or not 10mm2. Many of those who identified it as acceptable related
the size of the conductor to the live conductors in the swa, not the incoming supply. For
part d a large number of Students failed to identify the presence of the armour in parallel,
giving parallel paths through main equipotential bonding as the reason. Many Students
incorrectly identified the difference as being due to the temperature between the R1 + R2
test and the Zs test.
Question 28 - A large number of Students were unable to determine the expected overall
insulation resistance of the installation. Many suggested that it would be equal to the circuit
insulation resistance, ie 200MΩ, a number decided that it would be 14 x 200MΩ and
others 0.07MΩ.
Question 29 - The majority of Students forgot to include the R1 + R2 value for the
distribution circuit in their calculation for the lighting circuit Zs.
Question 30 - A number of Students were unable to correctly indicate the system used for
the scenario and so losing a considerable number of marks. Many Students stated that the
pfc would be higher at the new distribution board “because it was further away”. A large
number of Students stated that the Pfc was measured to confirm disconnection time. From
these two typical incorrect responses it would appear that Students were unable to
distinguish between Pfc and earth fault loop impedance.
Question 31 required a suitable test method for the continuity of protective conductors for
the distribution circuit. Despite this being 30m from the main intake position and
terminating in a remote building, a number of Students opted to carry out the test with a
wander lead.
Question 32 was very poorly answered. The procedure for testing ring final circuit
continuity has appeared in one form or another in recent papers. A large number of
Students were unable to correctly describe the process and many indicated a total lack of
understanding of the procedure. Common errors being, only completing one or two parts
of the test, not cross connecting the conductors, failure to establish the expected values
correctly. A number appeared to believe that the end to end test was all that was required.

Question 33 required the student to describe the process for a direct test of the earth loop
impedance for a lighting circuit. Some answers included the removal of the earthing
conductor while all circuits were energised. Many did not specify the use of leads to GS38.
The extent of the answers given for a question part worth 9 marks was generally
inadequate.
Question 34 asked Students why the phase (line) loop + neutral loop value is divided by 4
to obtain the expected value for stage 2 of the ring final circuit continuity test.
Question 35 asked for the significance of measuring the Pfc for an installation. Many
Students related this to disconnection time or establishing an earth path exists. A large
number suggested that a protective device would not operate if its PSCC rating was too
high. Another common error was that the device would not disconnect in time if incorrectly
rated.
Question 36 required the student to describe the correct procedure for carrying out an
insulation resistance test on a lighting circuit. Students were generally unable to correctly
describe the testing process and disconnecting switches and controls without bypassing or
linking out was common. Students appear to believe that electronic equipment is simply
disconnected and not appreciating that the circuit has been broken and therefore not fully
tested. Many Students did not indicate the instrument used or any of the checks that
should be made on the test equipment before use.
Question 37 required Students to provide information on testing of 30mA RCDs. Very few
Students were able to identify the test currents applied, the need for tests at 0º & 180º and
appropriate disconnection times. A common error was stating a 200ms disconnection time
for a BS EN 61008-1 RCD.
Question 38 required the student to identify three competence requirements, given in GN3
for the Inspector. Students identified almost anything but the competence requirements
identified in GN3.
Question 39 required information relating to the ‘nature of the supply’ and most Students
failed to provide the items listed in IEE regs (16th edition) 313-01-01 or IEE regs (17th
edition) 313.1 with the type of earthing arrangement being a common error.
Question 40 asked when the inspection and testing of a new installation would be carried
out. Many Students related their answer to periodic inspection requirements.
Question 41 asked for three items to be inspected during the first fix of a pvc conduit
installation. Many Students missed the reference to the conduit system and gave cable
compliance requirements.

Question 42 - Many Students related their answers to a periodic inspection or an extension
to an existing installation despite the information given in the scenario. Students were
required to identify all the documents that would be issued for this installation and the
majority failed to identify the need for more than one set of schedules for the installation.
Question 43 - Many Students were unable to correctly produce a diagram of the correct
earth fault loop path. Despite the question clearly stating ‘fully labelled’ many failed to label
their attempts. A large number failed to provide a complete path, omitting the supply
requirements some showing the system finishing at an installation electrode. A disturbing
number failed to isolate the pitch supply sockets from the TN-C-S earthing arrangement
connecting an electrode to the MET for the TN-C-S. A number of Students thought that the
fault current flowed to earth and then stopped!
Question 44 - Most Students, but not all, were able to identify whether the readings for
tests two and three were acceptable or not. Very few were able to give any realistic
reasons for the readings obtained. Conductors not connected, which was negated by the
values from test one. Where an incorrect polarity was identified this was often given
between the incorrect conductors or simply stated as ‘incorrect polarity’. In general
Students demonstrated they were aware of what was expected but had no understanding
of why and could not identify problems. This would support a lack of experience for many
Students.
Question 45 - Part c most Students provided a calculation for each circuit and gave this as
their answer. The question relates to the minimum breaking capacity of circuit breakers
fitted in a distribution board at the origin. The prospective fault current was therefore the
Pfc at the distribution board supply, not each circuit. When considered with the responses
to question 45 it is evident that the majority of Students have no understanding of
prospective fault current and its implications for the installation.
Students were unable to demonstrate an understanding of the requirements for the
preparation for inspection and testing, statutory requirements and BS7671.
Students should be advised to use drawings to help illustrate their answers, even where
this is not requested in the question. If it helps the student to clearly describe their answer
and reduce the amount of descriptive narrative required this will benefit the student in both
clarity of the answer and time taken.

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