2391-52 Inspection and Testing: exam guide and revision tips

The qualification brings together what used to be two separate awards: initial verification of new installations (the old 2391-50) and periodic inspection and testing of existing ones (the old 2391-51). Passing the combined 2391-52 shows you can do both.

• Safe isolation of circuits and installations before any work or testing.
• The inspection sequence: what to look at before any instrument comes out.
• The correct order of dead tests and live tests, and why the order matters.
• Completing certification: the Electrical Installation Certificate (EIC) for new work and the Electrical Installation Condition Report (EICR) for existing installations.
• Reading results against the limits in BS 7671 and IET Guidance Note 3 (GN3).

The 2391-52 is assessed in two parts: a written or online knowledge test and a practical assignment where you inspect and test a real installation under observation. You need to pass both. The knowledge test is where most candidates need the most practice, because it covers the whole of BS 7671 and GN3 rather than just the tests themselves.

Check the exact format, duration and pass requirements with your training centre, as these are set by City & Guilds and can change between qualification versions.

The knowledge test expects you to know each test, its purpose and its place in the sequence:

• Continuity of protective conductors, including main and supplementary bonding.
• Continuity of ring final circuit conductors (the end-to-end readings and what they tell you).
• Insulation resistance: test voltages from Table 64 and the minimum acceptable values.
• Site-applied insulation and protection by separation.
• Polarity, checked dead before the supply is connected.
• Earth fault loop impedance, both measured and calculated from Ze and R1 + R2.
• Prospective fault current at the origin and at relevant points in the installation.
• RCD operation: test currents, trip times and the additional protection requirements.
• Verification of phase sequence and functional testing of switches, isolators and assemblies.

For each one, know the instrument setting, the expected result and what a fail looks like. Questions often describe a reading and ask what you would do next.

The knowledge test is open book: you may take BS 7671 (the current amendment of the IET Wiring Regulations) and IET Guidance Note 3 into the exam. Mark the key tables before the day, especially the insulation resistance test voltages, maximum earth fault loop impedance values and RCD trip times. Finding a value quickly is a skill in itself.

• Learn the test sequence as a single ordered list. Many questions are really asking "which test comes next?".
• Practise reading GN3, not just BS 7671. The expected test methods and example forms live there.
• Know the difference between an EIC and an EICR, when each is used, and what the observation codes (C1, C2, C3, FI) mean on a condition report.
• Work through timed mock questions so the wording of the real exam feels familiar.
• For the practical, rehearse safe isolation until it is automatic: prove dead, lock off, prove the tester.

The fastest way to find your weak spots is a timed mock under exam conditions. FreeMocks has practice questions for inspection and testing topics, each with a full workout explaining the answer.