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Ring final circuits, step 2: the figure of eight, line to neutralWhy divide by four?

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8Take the neutral of one leg and join it to the line of the other leg, and the line of the first leg to the neutral of the other. That cross-connection is the figure of eight.

Then test at every socket on the ring, using a socket outlet adapter — no probes or clips needed, the leads plug straight in.

✋Every switch must be on. You need a closed circuit all the way round. A switched-off socket gives you an open-circuit reading and the tester's error symbol, and people waste a lot of time on it.

What you should expect

Expected R1 + Rn = (r1 + rn) ÷ 4

With those readings:
(0.01 + 0.52) ÷ 4 = 0.13 Ω
Why divide by four? With the figure of eight made up, the ring becomes one loop of resistance r1 + rn. Wherever you plug in, you are measuring two halves of that loop in parallel: each half is (r1 + rn) ÷ 2, and two equal halves in parallel give half of that again — (r1 + rn) ÷ 4. It's the parallel resistance rule doing the work.

Do you record it?

✋No. There is no R1 + Rn column on the schedule of test results. If you're a stickler you could note the highest value in the remarks column — and recording everything is good self-protection as well as good practice — but it is not required.
The readings at each socket should be substantially the same. A socket on a spur will read slightly higher, because of the extra length of cable out to it.

GN3 · 2.6.6 · p.63 · ring final continuity, step 2 ★

consumer unit L of one leg to N of the other test at EVERY socket on the ring R₁ + Rₙ = (r₁ + rₙ) ÷ 4 (0.01 + 0.52) ÷ 4 = 0.13 Ω ✋ Every switch on the ring must be ON — one switched-off socket reads open circuit and wastes ten minutes.
Cross-connect line and neutral at the board, then plug a socket adapter into every outlet. Readings should be substantially the same all the way round.

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