City & Guilds 2391-51 Exam Flashcards

Q: What qualification does 2391-51 identify?

It is the City & Guilds Level 3 Award in Periodic Inspection and Testing of Electrical Installations. It concerns existing installations and condition reporting, unlike 2391-50 initial verification; 2391-52 combines both pathways.

Q: How is City & Guilds 2391-51 assessed?

Candidates must pass the open-book, invigilated 2391-051 online multiple-choice test and successfully complete the 2391-501 practical assignment. The online test has 40 items, lasts 90 minutes, and has an approximately 75% pass mark that City & Guilds may adjust for reliability.

Q: What is the official 2391-051 test blueprint?

The 40 online questions allocate 5 to Outcome 1 requirements, 2 to Outcome 2 safety management, 7 to Outcome 3 inspection, and 26 to Outcome 4 testing. Outcome 5 practical performance has zero online questions because it is assessed in the mandatory assignment.

Q: How are these 50 flashcards allocated to the official outcomes?

Scaling the 5/2/7/26 blueprint by 1.25 gives 6.25/2.5/8.75/32.5 cards. The whole-card allocation is 6/3/9/32; the tied half-card remainder is assigned to the smaller safety outcome to preserve meaningful coverage.

Q: Which reference materials are permitted for 2391-051?

The current City & Guilds guide permits paper copies of BS 7671, the IET On-Site Guide, and IET Guidance Note 3 for the e-volve online test. Electronic copies are not permitted in externally marked assessments, and publications must comply with the current annotation rules.

Q: Which BS 7671 edition should a candidate use in 2026?

BS 7671:2018+A4:2026 has been published. The IET transition page says the A3:2024 Brown Book remains valid until 15 October 2026, while City & Guilds says assessment tasks will be aligned with Amendment 4 as documentation is updated. Candidates should confirm the edition required by their centre and current assessment documents.

Q: Who should take 2391-51?

It is intended for electricians with a relevant Level 3 Electrotechnical qualification or similar who already have enough knowledge and experience to inspect and test safely. City & Guilds explicitly says it is not suitable for industry newcomers or people with limited electrotechnical experience.

Q: What is the 2391-51 retake waiting period?

City & Guilds does not publish a fixed 2391-51 waiting period or a special rule after three failures in the current public qualification handbook. Candidates must obtain the current component-resit arrangements from their approved centre.

Question 1

What distinguishes periodic inspection from initial verification?

Accepted Answer

Periodic inspection evaluates an existing installation's condition for continued service. Initial verification confirms new work or an alteration before it is placed into service.

Question 2

Why may an existing installation require periodic inspection and testing?

Accepted Answer

To identify deterioration, damage, defects, changes in use, or other conditions that could affect safety, and to judge whether the installation remains suitable for continued service.

Question 3

How do statutory and non-statutory documents differ in periodic inspection?

Accepted Answer

Statutory documents impose legal duties applicable in the relevant UK nation. BS 7671, IET Guidance Note 3, and HSE guidance provide technical or safety guidance used to meet and evidence those duties.

Question 4

What must be agreed before the extent and limitations of a periodic inspection are set?

Accepted Answer

The inspector and the person ordering the work must agree what installation is covered and any justified limitations. The report must record the extent, each limitation, and its reason.

Question 5

What makes a sampling plan defensible during periodic inspection?

Accepted Answer

It is representative, risk-based, agreed, and recorded. If sampled items reveal defects or inconsistent results, the inspector should reconsider and extend the sample as needed.

Question 6

Which records support a complete periodic inspection report?

Accepted Answer

The EICR, Schedule of Inspections, Schedule of Circuit Details, Schedule of Test Results, and guidance for recipients. Entries must accurately reflect the work, limitations, observations, and measured results.

Question 7

What should a safe system of work establish before periodic inspection begins?

Accepted Answer

Hazards, risk controls, isolation arrangements, permits or method statements where required, suitable tools and instruments, PPE, access controls, and how unsafe situations will be reported.

Question 8

Why is a voltage indicator proved both before and after proving dead?

Accepted Answer

The first proof confirms the indicator works before use; the second confirms it did not fail during the check. A dead indication is trustworthy only when the indicator works on both sides of the test.

Question 9

Who can be harmed when safe isolation is omitted?

Accepted Answer

The inspector, workers, occupants, and public can face shock, burns, arc effects, fire, or unexpected operation. Planned isolation must also protect critical systems from harmful supply loss.

Question 10

What is the purpose of the Schedule of Inspections during an EICR?

Accepted Answer

It provides a systematic record of the installation features examined. It shows what was inspected, what was not applicable, and where the report's stated extent or limitations affected coverage.

Question 11

How may human senses support inspection without creating a new hazard?

Accepted Answer

Sight identifies damage and poor workmanship; smell or hearing may reveal overheating or arcing. Any closer examination or touch must be justified and performed only under safe conditions, normally after isolation.

Question 12

What do the two characteristic numerals in an IP code describe?

Accepted Answer

The first numeral describes protection against access to hazardous parts and solid objects. The second describes protection against water. An X means that characteristic was not specified or tested.

Question 13

What does EICR classification code C1 mean?

Accepted Answer

Danger is present. There is an immediate safety risk, so the inspector should advise that immediate remedial action is required and take appropriate action under the agreed safety procedure.

Question 14

What does EICR classification code C2 mean?

Accepted Answer

The condition is potentially dangerous. It is not necessarily causing danger at that instant, but urgent remedial action is required because a foreseeable event or fault could create danger.

Question 15

What does EICR classification code C3 mean?

Accepted Answer

Improvement is recommended. The observed condition is not classified as dangerous or potentially dangerous, but improving it would enhance safety or bring protection closer to the current standard.

Question 16

When is the EICR code FI appropriate?

Accepted Answer

When further investigation is required without delay to determine whether danger or potential danger exists. FI is not a substitute for completing an inspection that can reasonably be completed now.

Question 17

Which observation codes make the overall EICR assessment Unsatisfactory?

Accepted Answer

Any C1, C2, or FI observation results in an Unsatisfactory overall assessment. C3 alone does not make the report Unsatisfactory.

Question 18

Does departure from the newest BS 7671 edition automatically justify an EICR code?

Accepted Answer

No. An older installation is not automatically unsafe because requirements changed. The inspector classifies the present safety risk and records relevant observations rather than coding edition age alone.

Question 19

Why does City & Guilds state that periodic inspection has no recommended fixed test sequence?

Accepted Answer

The installation is already in service, and its condition, records, extent, limitations, connected equipment, and risks vary. The inspector selects a safe, logical sequence appropriate to the actual installation.

Question 20

When may a usual test be omitted or adapted during periodic inspection?

Accepted Answer

Only when existing information, installation conditions, safety, or risk justifies the decision. The inspector must still obtain sufficient evidence and record any resulting limitation or adapted method.

Question 21

Why must test instruments be maintained, calibrated, and checked before use?

Accepted Answer

To confirm they are safe, suitable, and capable of producing dependable measurements. A calibration label alone does not replace inspection, functional checks, and lead checks before and after use where appropriate.

Question 22

What is the safety purpose of GS38-compliant test leads and probes?

Accepted Answer

They reduce shock, arcing, and short-circuit risk through suitable insulation, finger barriers, minimal exposed conductive tips, and appropriate protective features such as fused leads where required.

Question 23

What does continuity testing of a protective conductor establish?

Accepted Answer

That the protective path is electrically continuous and has a resistance consistent with its length, material, and cross-sectional area, supporting fault-current flow and protective-device operation.

Question 24

What is the first purpose of end-to-end continuity tests on a ring final circuit?

Accepted Answer

To confirm that each ring conductor forms a complete loop. Unexpectedly high, low, or unequal readings may indicate a break, interconnection, poor joint, or conductor-size inconsistency requiring investigation.

Question 25

Why are cross-connected measurements taken around a ring final circuit?

Accepted Answer

They help verify polarity and continuity at each point and expose irregularities. Readings should follow a plausible pattern; a single convenient value is not enough if the pattern suggests a spur, bridge, or fault.

Question 26

What is insulation-resistance testing intended to reveal?

Accepted Answer

It checks whether insulation adequately separates live conductors from each other and from Earth. Low readings may indicate deterioration, moisture, damage, contamination, or connected equipment affecting the test.

Question 27

How should insulation-resistance testing be adapted for vulnerable connected equipment?

Accepted Answer

Disconnect vulnerable equipment where practicable. If a non-SELV/PELV circuit up to 500 V is tested at the permitted reduced 250 V DC, its minimum remains 1 megohm. Record the method and limitation.

Question 28

What common BS 7671 insulation-resistance values should be distinguished?

Accepted Answer

SELV and PELV circuits are generally tested at 250 V DC with a 0.5 megohm minimum. Circuits up to and including 500 V, other than SELV or PELV, are generally tested at 500 V DC with a 1 megohm minimum.

Question 29

What does a polarity test verify on an existing installation?

Accepted Answer

That line, neutral, and protective conductors are connected in the intended positions, and that single-pole devices such as switches and protective devices are connected in the line conductor where required.

Question 30

During periodic testing, what relationship is an earth-electrode measurement intended to quantify?

Accepted Answer

It assesses the resistance of the electrode system to the general mass of Earth. The method must account for parallel paths and test conditions so the result represents the electrode arrangement being evaluated.

Question 31

What is external earth fault loop impedance, Ze?

Accepted Answer

The earth fault loop impedance external to the consumer's installation, measured or otherwise determined at the origin with the installation side arranged safely for the selected method.

Question 32

What is earth fault loop impedance, Zs, for a final circuit?

Accepted Answer

The total impedance of the earth fault loop for that circuit. It includes the external loop and the circuit line and protective conductor paths, often expressed conceptually as Ze plus R1 plus R2.

Question 33

Why is prospective fault current established at relevant points?

Accepted Answer

To verify that protective and switching equipment has adequate breaking or withstand capacity. The relevant value reflects the greater applicable prospective short-circuit or earth fault current at that point.

Question 34

What does a phase-sequence test establish?

Accepted Answer

It confirms the order of phases in a multiphase system. Correct sequence matters for equipment such as motors and for consistency when circuits, boards, or supplies are connected or altered.

Question 35

What does operating an RCD's integral test button prove?

Accepted Answer

It provides a functional check that the device can mechanically operate from its internal test circuit. It does not measure actual trip time or replace instrument testing required by the current inspection specification.

Question 36

Why should an inspector avoid applying one memorised trip time to every RCD?

Accepted Answer

Permitted performance depends on the device type, rated residual current, time-delay characteristics, product standard, test method, and purpose. Results must be checked against the current requirement for that device.

Question 37

What is the purpose of functional testing during periodic inspection?

Accepted Answer

To confirm that switchgear, controls, interlocks, protective devices, and related equipment operate as intended where their operation affects safety. It complements visual inspection and electrical measurement.

Question 38

How can voltage drop be assessed using measured conductor resistance?

Accepted Answer

Use the complete current-path resistance, correct it for operating temperature, and multiply by design current. Conceptually, Vd = Ib x corrected path resistance.

Question 39

How does conductor temperature affect resistance-based test interpretation?

Accepted Answer

Metallic conductor resistance rises with temperature. Correct a cool-circuit reading before comparing it with an operating-temperature limit, and record the assumptions used.

Question 40

How can parallel conductive paths mislead continuity or loop measurements?

Accepted Answer

They can lower the measured resistance and mask a broken or poor intended conductor. Inspect the arrangement, isolate parallel paths where safe and necessary, or use another method to interpret the result correctly.

Question 41

Why are test leads nulled or compensated before low-resistance testing?

Accepted Answer

Lead resistance can be significant compared with the conductor under test. Compensation removes or accounts for that contribution so the recorded value represents the installation rather than the leads.

Question 42

How can connected loads affect periodic test results?

Accepted Answer

Loads and electronic equipment can create parallel paths, leakage, stored energy, or damage risk. Identify connected equipment, isolate it where required, and select a safe test method.

Question 43

What instrument characteristics must match the proposed electrical test?

Accepted Answer

Instrument type, measurement range, display resolution, output voltage or current, safety category, lead condition, and protective features must suit the circuit, expected value, and test environment.

Question 44

What makes verification of a test result stronger than checking one limit?

Accepted Answer

Compare it with current requirements, circuit data, related measurements, reliable previous records, instrument uncertainty, and site conditions. Investigate inconsistent evidence.

Question 45

Does every test result outside a current design value automatically receive the same EICR code?

Accepted Answer

No. The inspector determines the safety significance from the installation, protective measures, measurement quality, and foreseeable faults. The code communicates risk, not just numerical nonconformity.

Question 46

What question is answered by verifying a circuit's Zs result?

Accepted Answer

Whether the earth fault loop is sufficiently low for the selected protective measure and device to achieve the required fault protection, including disconnection performance under the applicable conditions.

Question 47

What must insulation testing confirm for an electrically separated circuit?

Accepted Answer

That the separated circuit remains insulated from Earth and from other circuits as required for the protective measure. Connected equipment and intentional components must be considered before choosing the method.

Question 48

What principle governs live testing during periodic inspection?

Accepted Answer

Use live testing only where it is necessary to obtain the required evidence and can be performed with suitable precautions by a competent person. Plan the method to minimise exposure and avoid unnecessary live work.

Question 49

Why should numerical results be entered on the EICR schedules instead of only a tick or 'pass'?

Accepted Answer

Actual values show what was measured, support compliance checks and classification, allow later review or trend comparison, and make clear which circuits and devices were tested.

Question 50

What must happen before an installation is returned to service after testing?

Accepted Answer

Remove temporary links and instruments, reconnect equipment correctly, replace covers and barriers, confirm safe operating condition, perform appropriate functional checks, and report any unresolved unsafe condition.

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