Inspection & Testing
Testing & Inspection · C&G 2365 Unit 304 / C&G 2391 · Full course section in Plus
The sequence is the discipline: continuity of protective conductors, ring final continuity, and are proved dead, before earth-fault loop , and RCD operation are checked live. Doing them in order means each test is only performed on a circuit the previous tests have already made safe to test.
Each measurement has a why. catches damaged cables before they leak; catches the switch wired into the neutral; loop proves a fault would actually trip the protection fast enough.
This is the heart of Unit 304 and the 2391 inspection qualification, and our ordering exercises and practice questions train the sequence until it runs itself.
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Original public revision material · A4:2026. For revision only; do not use samples to guide work on site.
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This question has not yet been reviewed by a qualified electrician. It is a community draft: check anything you plan to act on against BS 7671 and your own supervisor before you rely on it. Completing it does not make you competent, certified or registered.
Community draft — not yet reviewedWhat this means
This question has not yet been reviewed by a qualified electrician. It is a community draft: check anything you plan to act on against BS 7671 and your own supervisor before you rely on it. Completing it does not make you competent, certified or registered.
Community draft — not yet reviewedWhat this means
This question has not yet been reviewed by a qualified electrician. It is a community draft: check anything you plan to act on against BS 7671 and your own supervisor before you rely on it. Completing it does not make you competent, certified or registered.
Community draft — not yet reviewedWhat this means
This question has not yet been reviewed by a qualified electrician. It is a community draft: check anything you plan to act on against BS 7671 and your own supervisor before you rely on it. Completing it does not make you competent, certified or registered.
Common questions
- Can I try Inspection & Testing free on this page?
- Yes. The public sample below accepts answers and gives feedback and retries without an account, payment or energy. It is a short revision sample, not the complete course or a full mock paper. The full course section requires Plus.
- Where does Inspection & Testing sit in the City & Guilds scheme?
- Inspection & Testing maps to Unit 304 / C&G 2391. On TradeTraining it lives in the Testing & Inspection section as bite-size lessons with practice questions.
- Why do dead tests come before live tests?
- Because the dead tests prove the installation is safe to energise at all. Continuity, and faults are found while nothing can hurt you; only once those pass does the circuit get power for loop impedance and RCD tests. Reversing the order means energising an unproven installation.
Explore key terms
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Continuity testing
Low-resistance measurement proving that conductors which must be complete actually are. That means protective conductors back to the earthing terminal, bonding conductors to services, and the legs of ring final circuits. Performed dead with a low-ohm meter, it is the first step of the test sequence because everything after it assumes the earth path exists.
Read the full Continuity testing glossary entryInsulation resistance
The resistance between conductors that should be completely separated from each other. It is measured in megohms, line to neutral and each to earth, with a test instrument applying an elevated DC voltage. Healthy insulation reads very high; damaged cables, moisture or pinched conductors show up as a low reading long before they show up as a shock or a fire.
Read the full Insulation resistance glossary entryPolarity
Verification that conductors are connected the right way round throughout an installation. Single-pole switches and protective devices must sit in the line conductor, the centre contact of screw lampholders on line, and socket terminals wired as marked. A polarity fault can leave equipment live when switched off — which is why it is checked dead and confirmed again live.
Read the full Polarity glossary entryZsEarth Fault Loop Impedance
The total opposition to current around the loop a fault current would travel. That loop runs from the supply, along the line conductor to the fault, and back through the protective conductor and the earthing. It is the supply's own part (Ze) plus the circuit's R1 + R2, the resistance of its line and protective conductors. A low Zs lets a big fault current flow, which trips the protective device quickly, so electricians measure it and compare it with the maximum allowed for that device.
Read the full Zs glossary entryZeExternal Earth Fault Loop Impedance
The portion of the earth fault loop that lies outside the installation — the supply transformer winding, the distributor's cables and the earth return path, measured at the origin with the installation's own parallel paths disconnected. Ze depends on the earthing system: a TT installation relying on an electrode in soil sees a far higher value than a TN supply with a metallic return.
Read the full Ze glossary entryEICRElectrical Installation Condition Report
The report produced by a periodic inspection of an existing installation, recording its condition against the current edition of BS 7671. Observations are classified by urgency — C1 for danger present, C2 for potentially dangerous, C3 for improvement recommended, and FI where further investigation is needed — and a C1 or C2 makes the report unsatisfactory.
Read the full EICR glossary entry