Ring Final Circuit

Step 1 — end-to-end readings

With both legs of the ring disconnected from the board, measure each conductor end to end: line (r1), neutral (rn) and circuit protective conductor (r2).

On a ring wired in the same cable throughout, r1 and rn run in identical conductors over an identical route, so they should read within a few percent of one another. This calculator flags a difference of more than 5%, which usually means a broken ring, an interconnection, or a spur mistaken for part of the ring. The CPC is normally a reduced size, so r2 is expected to be higher — typically about 1.67× r1 for a 2.5/1.5 mm² twin-and-earth ring.

Step 2 — cross-connect and measure

Cross-connect line of one leg to neutral of the other, and vice versa, then measure between line and neutral at each socket. Every reading should be substantially the same, at about (r1 + rn) / 4.

Step 3 — line to CPC

Repeat the cross-connection with line and CPC. The reading at each socket should again be substantially the same, and equal to (r1 + r2) / 4 — the figure this calculator gives you. That value is the circuit's R1+R2, and it is what you record on the Schedule of Test Results.

A reading noticeably higher than expected at one socket points to a spur; readings that climb and fall as you move round the ring point to a ring that is not actually continuous.