The BS 7671 testing sequence: dead tests, live tests and the order that matters

Why the order exists at all

Inspection and testing moves from the safest activity to the least safe. You look before you touch, you test dead before you test live, and you only energise once the dead tests say the installation is sound. Reversing that means putting a supply onto a circuit whose insulation you have not yet proved.

BS 7671 sets the tests out in Part 6. The sequence below follows the order used in the IET Guidance Note 3 and taught on the C&G 2391 route, which is what an assessor will expect to see reflected in your results.

Before anything: safe isolation and the visual inspection

Prove the tester, isolate, lock off, prove dead, prove the tester again. Nothing that follows is defensible if this step was skipped.

The visual inspection then catches most of what an EICR will end up coding. Damage, overheating, missing barriers, unsuitable equipment for the location, absent notices and obvious departures from the current standard are all found by looking, not by measuring.

• · Agree and record the extent and limitations in writing first
• · Check the supply, cut-out, tails, main switch and earthing arrangement
• · Walk the installation room by room against the condition schedule

The dead tests, in order

All four dead tests happen with the installation isolated. Keep them in this order — continuity results feed the polarity check, and insulation resistance is meaningless if the conductors are not continuous in the first place.

• · 1. Continuity of protective conductors — R1+R2 on radials, and r1, rn, r2 on ring finals
• · 2. Continuity of ring final circuit conductors — the three-step method that also proves there are no interconnections
• · 3. Insulation resistance — 500 V DC between live conductors and between live conductors and earth, with sensitive equipment disconnected
• · 4. Polarity — confirmed dead by continuity before it is ever confirmed live

What the insulation resistance figures mean

For a 230/400 V circuit the minimum acceptable value is 1 MΩ at 500 V DC. Anything at or just above that minimum is a warning rather than a pass — a healthy domestic circuit usually reads in the hundreds of megohms.

A reading of, say, 1.4 MΩ across a whole board is almost always the sum of many small leakage paths rather than one fault. Split the board and test circuit by circuit until the low reading isolates itself.

The live tests, in order

Energise only once the dead tests are complete and satisfactory. The live tests confirm that the installation will disconnect fast enough when a fault occurs.

• · 5. Polarity confirmed live at the origin
• · 6. Earth fault loop impedance, Ze at the origin and Zs at the far point of each circuit
• · 7. Prospective fault current — the higher of prospective short-circuit current and prospective earth fault current
• · 8. RCD operating times at the rated residual current and at five times rated current, plus the test button
• · 9. Functional testing of switchgear, interlocks, controls and any AFDDs or SPDs fitted

Reading Zs correctly

Measured Zs must be below the maximum tabulated value for the protective device. The tables in Chapter 41 assume conductors at their operating temperature, so most inspectors compare measured values against 80 % of the tabulated figure, which is the rule-of-thumb correction for a cold measurement.

Disconnection time is 0.4 seconds for final circuits up to 63 A on a TN system, and 5 seconds for distribution circuits. On a TT system the RCD is doing the work, so the loop impedance limit is far more generous but the RCD test result becomes critical.

Where Amendment 4 changed the picture

BS 7671:2018+A4:2026, published on 15 April 2026, brings battery storage under closer scrutiny in Chapter 57, adds inspection schedule fields for surge protective devices and arc fault detection devices, and expects photographic or thermal evidence to be attached where a defect is being evidenced.

For testing itself the sequence is unchanged. What changed is what you record alongside it.

Recording the results

Every measured value goes on the schedule of test results, with the instrument serial numbers and the date. Anything you could not test is a limitation, and limitations agreed after the fact look like excuses.

Use the Certi maximum Zs tool to check each loop reading against the device limit as you go, and the code checker to settle the coding before you leave site.