2.2 Non-Statutory Documents

What Makes a Document Non-Statutory?

A non-statutory document is a standard, guidance note, or code of practice that has not been enacted as law. There is no criminal penalty for non-compliance in itself. However, non-statutory documents are critically important because compliance with them is a common way to demonstrate compliance with statutory duties. In court, following a recognised standard such as BS 7671 can be used as evidence that the duty holder acted reasonably and met their obligations under the Electricity at Work Regulations 1989.

For the 2391-52 inspector, non-statutory documents are the day-to-day working references — the documents you carry on site, consult during inspection, and verify installations against. Three of them (BS 7671, GN3, and the On-Site Guide) are permitted in the exam room, reflecting the open-book nature of the 2391-52 assessment.

The Key Non-Statutory Documents

BS 7671:2018+A4:2026 — IET Wiring Regulations (18th Edition, Amendment 4)

BS 7671 is the UK national standard for the design, selection, erection, and verification of electrical installations. Despite being called "Regulations," it is a non-statutory standard published jointly by the IET (Institution of Engineering and Technology) and BSI (British Standards Institution).

The current version is BS 7671:2018+A4:2026, published on 15 April 2026 and implementable immediately. The previous version — BS 7671:2018+A2:2022 as amended by A3:2024 — is due to be withdrawn on 15 October 2026, six months after A4 was published. Until that date the two co-exist, which is why you should confirm with your centre which text your paper is written to. This is a critical currency point for the exam: from 15 October 2026 A4:2026 is the only current amendment.

For the inspector, BS 7671 defines:

• The fundamental principles for safety (Part 1) — the basis for all installation requirements
• Definitions (Part 2) — including the classification of external influences (Appendix 5)
• General characteristics (Part 3) — intended use, supply characteristics, and external influences
• Protection for safety (Part 4) — protection against electric shock, thermal effects, overcurrent, and fault currents
• Selection and erection (Part 5) — how equipment is chosen and installed
• Inspection and testing (Part 6) — this is where the inspector's work is defined in the standard, covering initial verification and periodic inspection
• Special installations or locations (Part 7) — additional requirements for specific environments
• Model forms (Appendix 6) — Electrical Installation Certificates (EIC), Minor Electrical Installation Works Certificates (MEIWC), and Electrical Installation Condition Reports (EICR)

IET Guidance Note 3 (GN3) — Inspection & Testing, 10th Edition (2026)

IET Guidance Note 3 (GN3) is the single most important non-statutory document for the 2391-52 exam. It is the practical companion to BS 7671's Part 6, expanding the standard's verification requirements into step-by-step guidance. GN3 provides:

• The sequence of tests for initial verification and periodic inspection — the order in which tests must be carried out for safety and validity
• Detailed test procedures for continuity, insulation resistance, polarity, earth fault loop impedance, prospective fault current, and RCD operation
• The pass/fail criteria for each test, referenced to BS 7671 values
• Guidance on sampling during periodic inspection — how to select circuits and the extent of testing
• Guidance on observation coding — the C1 (danger present), C2 (potentially dangerous), C3 (improvement recommended), and FI (further investigation) codes used on EICRs
• The recommended periods between inspections — frequencies for various installation types

The current edition is the 10th Edition (2026), aligned with BS 7671:2018+A4:2026. Its ISBN is 9781837240487. GN3 is permitted in the exam room and is the document whose content is most directly tested in the 2391-52 assessment.

IET On-Site Guide (OSG)

The IET On-Site Guide (OSG) is a simplified, pocket-sized reference derived from BS 7671. It provides:

• Tabulated values for cable sizing, current-carrying capacity, and voltage drop in common scenarios
• Simplified calculation methods for earth fault loop impedance and disconnection times
• Ready-to-use guidance for typical domestic and small commercial installations
• Permitted in the exam alongside BS 7671 and GN3

The OSG is not a substitute for BS 7671 where complex or unusual installations are involved, but it is an invaluable quick reference for routine work.

HSE Guidance Note GS38 — Electrical Test Equipment for Electricians

HSE Guidance Note GS38 is published by the Health and Safety Executive (HSE) and specifies requirements for test instruments and leads used in electrical testing. It covers:

• Test lead construction — insulated, shrouded, and rated for the voltage and current encountered
• Probe design — finger guards to prevent the user's fingers from slipping onto live parts
• Fuse requirements in test leads where necessary to protect against fault currents
• Instrument category (CAT) ratings appropriate to the measurement environment
• Exposed metal at the probe tip kept to the minimum needed to make contact, and current-limiting resistors or fuses in the leads

GS38 is a safety document, not a wiring document. The inspector must ensure all test instruments comply with GS38 before use — non-compliant leads or probes can cause injury or death during testing. GS38 is not listed as an exam-permitted document (it is not needed in the exam room), but knowledge of its requirements is examinable.

Other IET Guidance Notes

The IET publishes a suite of guidance notes supporting BS 7671. Those less central to 2391-52 include:

• GN1 — Selection and Erection of Equipment
• GN7 — Special Locations (e.g., bathrooms, swimming pools, saunas, medical locations)
• GN8 — Earthing & Bonding

These are referenced where the installation being inspected falls within their scope.

Why GN3 Is the Most Important Document for the 2391-52

The 2391-52 exam tests the inspector's knowledge of how to inspect and test electrical installations. GN3 is the document that translates BS 7671's requirements into practical, step-by-step procedures. While BS 7671 tells you what must be verified, GN3 tells you how to verify it — the instrument settings, test connections, sequence, and pass criteria. GN3 should be the most heavily referenced document during exam preparation.

Non-Statutory Documents Comparison Table