R1+R2 Continuity Testing
Testing & Inspection · C&G 2365 Unit 304 / 2391 · Full course section in Plus
Continuity of protective conductors is the first dead test, and the usual method links the line conductor to the at the board, then measures between line and cpc at each point on the circuit. The reading at each point is for that point — the loop the fault would take through the circuit's own conductors.
The instrument is a low- ohmmeter, and the leads must be nulled first: a couple of tenths of an ohm of test lead looks exactly like a slightly loose termination once you are reading fractions of an ohm. The wander-lead method is the alternative where linking at the board is impractical, at the cost of a long lead whose own resistance you must account for.
The number matters twice. It confirms the protective conductor is continuous, and it feeds the calculation: Zs equals plus . A reading that drifts, or that is far lower than the cable length suggests, usually means a parallel path through metalwork rather than a good connection.
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Common questions
- Can I try R1+R2 Continuity Testing free on this page?
- This guide is free to read, but there is no public quiz specifically for this topic on this page. Browse public practice samples for other subjects, or create an account for the learning path. The full course section requires Plus.
- Where does R1+R2 Continuity Testing sit in the City & Guilds scheme?
- maps to C&G 2365 Unit 304 / 2391. On TradeTraining it lives in the Testing & Inspection section as bite-size lessons with practice questions.
- What does R1+R2 actually stand for?
- R1 is the of the circuit's line conductor and R2 the resistance of its protective conductor. Measured together, they give the resistance of the path a line-to-earth fault would take within the circuit itself.
- Why do you null the test leads first?
- Because you are measuring in fractions of an ohm and the leads themselves have . Without nulling, every reading is inflated by the leads and a healthy circuit can look like a poor one.
Explore key terms
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R1+R2
The combined resistance of a circuit's line conductor (R1) and its circuit protective conductor (R2), measured end-to-end during dead testing. It proves the protective conductor is continuous, and added to Ze it predicts the circuit's earth fault loop impedance before the supply is ever switched on.
Read the full R1+R2 glossary entryCPCCircuit Protective Conductor
The earth wire of a circuit. It links the metal parts of the equipment the circuit feeds back to the main earthing terminal. Normally it carries no current; if a fault makes that metalwork live, it carries the fault current so the fuse or breaker switches off. In UK wiring it is green and yellow, or bare inside twin-and-earth cable, with green-and-yellow sleeving wherever it is exposed.
Read the full CPC glossary entryContinuity 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 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 entry