Ring Final Circuit Testing
Testing & Inspection · C&G 2365 Unit 304 / 2391 · Premium section
Step one measures each leg end to end with the ring opened at the board: r1 for the line conductors, rn for the neutrals, r2 for the protective conductors. On a standard ring in 2.5 mm² with a 1.5 mm² cpc, r2 comes out around one and two-thirds times r1, because the smaller cpc has the higher resistance per metre.
Step two cross-connects line to neutral and reads at every socket. On a healthy ring, every socket reads about a quarter of r1 plus rn, and — this is the tell — reads substantially the same at every one of them. Step three repeats the cross-connect between line and cpc; those readings are the circuit's , and the highest of them belongs to the electrically most distant point.
The fault patterns are readable. A reading that climbs the further round you go says the ring is broken and you are measuring along a radial. One socket much higher than its neighbours says a spur. Readings that make no sense at all usually mean an interconnection — two rings crossed somewhere in the loft.
Common questions
- Is there a free Ring Final Circuit Testing quiz?
- Testing sits in the Testing & Inspection section, which is part of TradeTraining Premium — but the app is free to start, sample questions are open to everyone, and the free sections cover the fundamentals first.
- Where does Ring Final Circuit Testing sit in the City & Guilds scheme?
- Testing maps to C&G 2365 Unit 304 / 2391. On TradeTraining it lives in the Testing & Inspection section as bite-size lessons with practice questions.
- Why should every socket read the same in step two?
- Because on a continuous ring each socket sits at the junction of two paths whose resistances add to the same total wherever you stand. Substantially equal readings are the proof the ring is closed; a rising set of readings means it is not.
- What does it mean if r2 is about 1.67 times r1?
- It is what you expect on a ring wired in 2.5 mm² with a 1.5 mm² protective conductor: the cpc has a smaller cross-section, so more resistance per metre, in roughly that ratio. A very different ratio suggests a different cable or a wiring fault.