Insulation resistance
The 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 . 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.
Where to look it up: BS 7671 Part 6.
Where Insulation resistance fits in the learning path
The Testing & Inspection section covers these units:
- Initial Verification & Dead Testing
- Live Testing
- Inspection & Certification
Curriculum mapping: C&G 2365 Unit 304 / 2391.
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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.
Continuity testing
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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 Continuity testing 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 Polarity entryEICR — Electrical 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 EICR entryDC — Direct Current
Direct current flows in one direction, although its size can vary. A battery supplies DC, while an inverter can convert DC from a battery into AC for suitable loads. DC does not mean low voltage or harmless: direction of flow and voltage level are separate ideas. Insulation resistance instruments use a DC test voltage, but that is not the normal supply voltage of the circuit.
Read the DC entryA definition is a start. Using it in a real question is where it sticks.