R1+R2 Ring Final Circuit Test: Why Your Values Don't Match

If you’ve ever tested a ring final circuit and found that your R1+R2 readings vary from socket to socket, you’re not alone. It’s one of the most common headaches electricians face during inspection and testing. The good news: there’s usually a perfectly logical explanation.

This guide walks you through the 3-step ring final circuit continuity test, explains what the readings should be, and covers the five most common reasons your values don’t match — so you can diagnose the issue with confidence.

What Is a Ring Final Circuit?

A ring final circuit is a circuit where the line, neutral, and earth conductors each form a loop — starting at the distribution board, running through every socket outlet on the circuit, and returning back to the same terminals at the DB. This means every socket on the ring is fed from two directions, which reduces voltage drop and allows a 32A circuit to serve multiple 13A socket outlets.

Ring circuits are covered under Regulation 314.1 of BS 7671, and testing their continuity is part of the dead tests required under Chapter 61 (Initial Verification).

The 3-Step Ring Final Circuit Test

The continuity test for a ring final circuit is carried out in three steps. The circuit must be isolated and disconnected from the distribution board before you begin.

Step 1: End-to-End Resistance

At the distribution board, measure the resistance of each conductor pair end-to-end:

• r1 = Line to Line (L1 to L2)
• rn = Neutral to Neutral (N1 to N2)
• r2 = Earth to Earth (E1 to E2)

What to expect:

• r1 and rn should be approximately equal — they’re the same gauge of cable running the same route. If they differ significantly, suspect a break or interconnection.
• r2 will typically be higher than r1 — for standard 2.5/1.5mm² twin-and-earth cable, the CPC (earth) is 1.5mm² compared to the 2.5mm² live conductors, giving r2 a value roughly 1.67 times r1.

Worked example: For a 20-metre ring using 2.5/1.5mm² T&E:

• r1 ≈ 0.52 Ω
• rn ≈ 0.52 Ω
• r2 ≈ 0.87 Ω (0.52 × 1.67)

Step 2: Line–Neutral Cross-Connection

Connect the opposite legs of the line and neutral conductors together at the DB:

• Join L1 to N2
• Join N1 to L2

Now measure between Line and Neutral at every socket outlet on the circuit.

Expected reading: The values should be substantially the same at each socket, with a value of approximately (r1 + rn) / 4.

Using our example: (0.52 + 0.52) / 4 = 0.26 Ω

This step confirms the ring is continuous and verifies correct polarity at each socket.

Step 3: Line–Earth Cross-Connection (The Figure-of-8 Test)

Remove the Step 2 connections. Now cross-connect line and earth:

• Join L1 to E2
• Join E1 to L2

Measure between Line and Earth at every socket outlet.

Expected reading: Values should be substantially the same at each socket, with a value of approximately (r1 + r2) / 4.

Using our example: (0.52 + 0.87) / 4 = 0.35 Ω

This is the R1+R2 value for the circuit — the figure that goes on your Electrical Installation Certificate. The cross-connection creates a “figure-of-8” path through the ring, which is why this is sometimes called the figure-of-8 test.

What “Substantially the Same” Actually Means

BS 7671 uses the phrase “substantially the same” rather than giving a precise tolerance. In practice:

• Readings on ring sockets should be within about 0.05 Ω of each other
• A reading that deviates by more than 0.5 Ω from the expected value warrants investigation
• Readings should be roughly symmetrical — if you imagine the ring as a clock, sockets at 12 o’clock (mid-point) should read similarly to each other

Why Your R1+R2 Values Don’t Match

Here are the five most common reasons for unequal readings, ordered from most to least common.

1. Spurs on the Ring

This is by far the most common reason for differing values, and it’s completely normal.

A spur is a branch cable that feeds one or two sockets from a point on the ring. Unlike ring sockets (which are fed from two directions), a spur socket is fed from one direction only. This means current has to travel further, giving a higher resistance reading.

How to identify: If a socket reads higher than the others but the reading is stable and consistent, it’s very likely a spur. Check the wiring at the socket — if there’s only one cable entering the back of the socket (rather than two), it’s on a spur.

Is it a fault? No. This is expected behaviour and doesn’t need fixing.

2. Parallel Paths from Bonding Conductors

If supplementary bonding conductors are connected to metalwork (such as metal conduit, metal back boxes, or pipework) at various points around the ring, they create parallel paths for the test current. This makes the measured R1+R2 value artificially lower than it should be.

Worse, parallel paths can mask a broken CPC — the test might appear to pass even though the earth conductor is not continuous.

How to identify: If some readings are unexpectedly low, suspect parallel paths.

What to do: Where practical, disconnect supplementary bonding before testing. This gives you the true R1+R2 value and ensures you’re actually testing the ring conductor, not the bonding.

3. Loose or High-Resistance Connections

A poor terminal connection at a socket — perhaps a loose screw, corroded contact, or damaged conductor — adds resistance at that point. The socket will show a reading that is higher than expected by more than 0.5 Ω.

How to identify: A single socket with a reading significantly above the expected value, while all other sockets read normally.

What to do: Check the terminal connections at the offending socket. Tighten screws, clean contacts, and re-test. High-resistance joints can cause overheating and are a potential fire hazard.

4. Cross-Connections (Wrong Terminals)

If conductors are in the wrong terminals at a socket — for example, the line and neutral conductors from two different legs of the ring are swapped — you may get no reading at all, or wildly erratic values.

How to identify: A complete open circuit (infinite reading) at a socket during Step 2 or Step 3, or readings that make no sense compared to the rest of the ring.

What to do: Pull the socket out and check that all conductors are in the correct terminals. Correct the wiring and re-test.

5. A Broken Ring

If one leg of the ring conductor is broken (disconnected at some point), the circuit effectively becomes a radial. Readings will increase progressively from the DB toward the break, and then decrease again on the other side.

How to identify: A clear pattern of increasing then decreasing readings as you move around the ring. The Step 1 end-to-end readings may also show an anomaly — for instance, r1 might read open circuit if the break is in the line conductor.

What to do: Locate and repair the break. The point where readings are highest is closest to the break.

Quick Reference: Symptoms and Causes

Symptom	Likely Cause	Action
One or two sockets read higher, rest are consistent	Spur (normal)	Check wiring — single cable = spur
Some sockets read unexpectedly low	Parallel bonding paths	Disconnect bonding, re-test
One socket reads >0.5 Ω above expected	Loose connection	Inspect and tighten terminals
No reading / erratic values at a socket	Cross-connection	Check terminal wiring at socket
Readings increase toward a mid-point	Broken ring	Locate and repair break
r1 and rn differ significantly (Step 1)	Break or interconnection	Investigate before proceeding

Key Takeaways

1. The expected R1+R2 value is (r1 + r2) / 4 — calculate it before testing so you know what to look for.
2. Spur sockets will always read higher — this is normal and not a fault.
3. Disconnect supplementary bonding before testing to avoid false low readings.
4. Any deviation >0.5 Ω warrants investigation — check terminal connections.
5. No reading at a socket usually means a cross-connection — check the wiring at that point.

Practice and Further Study

This topic falls under Part 6: Inspection and Testing of BS 7671. Test your knowledge with our Part 6 practice quiz containing focused questions on testing procedures.

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