Electrical testing under BS 7671:2018 follows a fixed sequence set out in Chapter 64 and IET Guidance Note 3: dead tests first (continuity, ring final continuity, insulation resistance, polarity), then live tests (earth fault loop impedance, prospective fault current, RCD and AFDD operation), with earth electrode testing added on TT systems. Each test has its own pass criterion: insulation resistance at least 1.0 MΩ at 500 V DC, a 30 mA RCD tripping within 300 ms, Zs within the Chapter 41 maxima. This page indexes every testing guide on Certio with what each test proves, its typical limit and where to read the method.
- Dead tests are done with the supply isolated and locked off; live tests need the supply on. Never reverse the order.
- Every result goes on the schedule of test results, which is what a scheme assessor reads first.
- Limits come from BS 7671 (Chapter 41 for Zs, Table 64 for insulation resistance) and BS EN 61008/61009 for RCD trip times.
- A multifunction tester (MFT) does all of these tests; keep it calibrated and check it against a reference before use.
- Every reading should be compared against its limit on site, not back at the office.
Which test proves what?
| Test | What it proves | Typical limit or expectation | Guide |
|---|---|---|---|
| Continuity of protective conductors (R1+R2) | Every exposed-conductive-part has a continuous CPC back to the MET | Value consistent with cable length and CSA; used to predict Zs | Continuity Testing: R1+R2 Method, Wander Lead and Values |
| Ring final circuit continuity (r1, rn, r2) | Ring is complete with no interconnections or breaks | End-to-end readings; r2 about 1.67 times r1 for 2.5/1.5 mm² cable; cross-connected readings substantially equal at each socket | Ring Final Circuit Testing: r1, rn, r2 and R1+R2 Explained |
| Insulation resistance | No breakdown between live conductors and earth or between live conductors | At least 1.0 MΩ at 500 V DC for circuits up to 500 V (BS 7671 Table 64) | Insulation Resistance Testing Guide: Voltages, Minimums, Method |
| Polarity | Line, neutral and CPC land on the correct terminals; single-pole devices in the line conductor | Correct at every point tested | Polarity Testing Explained: Checks, Methods and EICR Codes |
| Main protective bonding | Extraneous-conductive-parts are bonded to the MET | Conductor sized to Regulation 544.1 and continuous | What is main protective bonding? Explained |
| External loop impedance (Ze) | Supply earth path is adequate | Typically up to 0.35 Ω TN-C-S, 0.8 Ω TN-S, 21 Ω TT (ENA typical maxima) | What is Ze? External earth fault loop impedance |
| Earth fault loop impedance (Zs) | Protective device will disconnect within the required time | Not more than the Chapter 41 maximum for the device, commonly checked at 80% of the tabulated figure | Earth Fault Loop Impedance Testing: Ze, Zs and Ipf Explained and Maximum Zs Values BS 7671: Tables, 80% Rule and Ze |
| Prospective fault current (Ipf) | Protective devices can safely interrupt the fault | Must not exceed the breaking capacity of any device | What is prospective fault current (PFC)? Explained |
| RCD operation | RCD disconnects at its rated residual current | 300 ms at 1x for general RCDs; 40 ms at 5x | RCD Testing Explained: Types, Test Currents and Trip Times |
| AFDD functional test | Arc fault detection device operates via its test button | Device trips on test; manufacturer's instructions | What is an AFDD? Arc fault detection devices explained |
| Earth electrode resistance (RA) | TT electrode provides an adequate earth | RA x IΔn not more than 50 V; in practice 200 Ω or less recommended for stability | Earth Electrode Testing for TT Systems: Methods and Limits |
| Three-phase checks | Phase rotation, balance and per-phase loop values | Correct rotation; Zs per phase within limits | Three-Phase Testing Basics for Domestic Electricians |
What are the dead tests and why do they come first?
Dead tests are carried out with the installation isolated, proved dead and locked off, so that a cable fault is found before the circuit is energised. Continuity of protective conductors (/guides/continuity-testing-r1-r2-method) confirms every exposed metal part has an earth path; the R1+R2 value also predicts the Zs you should see later. Ring final circuits get the three-step test in Ring Final Circuit Testing: r1, rn, r2 and R1+R2 Explained, which catches interconnections and broken legs.
Insulation resistance is tested at 500 V DC for 230 V and 400 V circuits, with a minimum of 1.0 MΩ under BS 7671 Table 64. Insulation Resistance Testing Guide: Voltages, Minimums, Method explains which conductors to test between, what to disconnect first and how to record a circuit that could not be tested. Polarity (/guides/polarity-testing-explained) confirms switches and fuses are in the line conductor. Main protective bonding is inspected and its continuity confirmed on the same visit; see What is main protective bonding? Explained.
What are the live tests?
Live tests are carried out with the supply restored. Start at the origin with Ze, measured with the main earthing conductor disconnected so that parallel paths do not mask a poor supply earth (/guides/what-is-ze-external-earth-fault-loop-impedance). Prospective fault current is measured at the same point and must not exceed the breaking capacity of any device; see What is prospective fault current (PFC)? Explained.
Zs is then measured at the furthest point of every circuit. What is Zs? Earth fault loop impedance explained defines the term, Earth Fault Loop Impedance Testing: Ze, Zs and Ipf Explained covers the method and the no-trip settings needed on RCD-protected circuits, and Maximum Zs Values BS 7671: Tables, 80% Rule and Ze tabulates the Chapter 41 maxima and the 80% rule of thumb used to correct for conductor temperature. RCDs are tested at rated residual current and at five times rated current; RCD Testing Explained: Types, Test Currents and Trip Times gives the 300 ms and 40 ms limits, and What is an RCD? Types AC, A, F, B and RCBOs explained explains the device types. AFDDs have a functional test only; see What is an AFDD? Arc fault detection devices explained and AFDD Requirements: Regulation 421.1.7 Explained.
What extra tests apply to TT and three-phase installations?
On a TT system the installation's own earth electrode provides the fault path, so its resistance must be measured. Earth Electrode Testing for TT Systems: Methods and Limits explains the three-terminal fall-of-potential method and the loop-tester alternative, and why a reading of 200 Ω or less is recommended for stability even though the arithmetic limit is RA x IΔn not exceeding 50 V. Outbuildings and garden supplies frequently involve a change of earthing system, and Outbuilding and Garden Supply: SWA, TT or PME Earth? covers when to export the PME earth and when to use a local electrode.
Three-phase boards add phase rotation, per-phase Zs readings and prospective fault current between lines; Three-Phase Testing Basics for Domestic Electricians runs through the sequence for a 400 V board. Cable questions that arise during testing, such as whether an undersized cable explains a high Zs, are covered in Cable Sizing and Volt Drop Basics: Ib, In, Iz and Table 4D5 and Cooker Circuit Design and Diversity: Sizing It Right.
Where do the results go?
Every result goes on the schedule of test results, the page of the certificate or report that a scheme assessor reads first. What is a schedule of test results? Explained explains each column, from circuit designation and protective device type to the measured Zs and RCD trip time, and How to fill in a schedule of test results, column by column shows how to complete it, including when to write LIM, N/A or N/V. The same schedule appears on the EIC for new work and the EICR for periodic inspection; EICR vs EIC: What's the Difference? (and Minor Works) explains which document applies. The full step-by-step is at How to Do an EICR Step by Step: Inspector's Workflow.
What instrument do I need?
All of the above is done with a multifunction tester. What is a multifunction tester (MFT)? Explained explains the functions, the BS EN 61557 accuracy requirements and what to check before you rely on a reading. There is no statutory calibration interval, but NICEIC and NAPIT expect evidence of ongoing accuracy, and annual calibration plus a daily check against a reference box is the accepted practice. Record the instrument serial number on the certificate; it is a required field on the BS 7671 model forms.
How Certio helps
Certio produces the EICR, EIC, Minor Works certificate and PAT records on the BS 7671 model forms and turns them into branded PDFs. Photograph the consumer unit and the circuit schedule drafts itself; point the phone camera at a Megger MFT-X1 and the reading goes straight into the schedule of test results, or dictate it while your hands stay on the probes. Suggested observation wording with the regulation reference is there for you to check and confirm. The judgement stays yours; the typing goes. Starter is free for 7 days, then £5 a month.