BS 7671 sets the installation requirements. The On-Site Guide gives practical guidance for installations within its scope. Guidance Note 3 develops inspection and testing. Choose the book for the task, then check that its edition matches the standard or assessment you are using.
These books work together, but they answer different questions. A learner choosing their first reference book needs a different starting point from an electrician preparing inspection records. Use the comparison below to decide what you need to look up.
Which book answers your question?
Start with the job you need the reference to do. The shorter book can be useful when its assumptions fit; the full requirement remains in BS 7671.
| Reference | Use it for | Check before relying on it |
|---|---|---|
| BS 7671 | Finding the requirement, its scope, definitions and exceptions. | Use the amendment specified for your work or assessment. Read the surrounding clauses and referenced material. |
| On-Site Guide | Practical guidance for common installation arrangements within its stated scope. | Check the installation and any table assumptions. It does not cover every design situation. |
| Guidance Note 3 | Understanding inspection, testing and recording results. | Use it alongside BS 7671 and the relevant equipment instructions. |
What the On-Site Guide covers
The IET describes the On-Site Guide as guidance for competent installers dealing with installations up to 100 A, three-phase. That headline limit does not mean every installation below it fits every example or table in the book.
Before using a tabulated arrangement, identify what it assumes about the installation. A convenient value is useful only when the actual circuit meets those conditions. If your situation falls outside the guidance, return to the relevant BS 7671 requirements and the design information for the job.
Try this as a desk exercise: a cable-selection example used one installation method, but the cable is now grouped with other circuits. Identify which assumptions have changed, then check the applicable current-carrying-capacity information and correction factors before recalculating. Explain why the earlier cable size needs checking again in the changed conditions.
When Guidance Note 3 is the useful next book
Guidance Note 3 focuses on inspection and testing of electrical installations. It is particularly relevant when your study or work involves verification, test results and the records that support them.
A productive reading session starts with one question: what does this inspection or test establish? Follow it through to the method, the result you need to record and the requirement against which the result is assessed. Keep those pieces together in your revision notes.
For example, if a practice explanation mentions earth fault loop impedance, separate the measured value from the limit you are comparing it with. Identify the conditions attached to that limit before deciding whether the comparison is valid. Looking up a number without its conditions leaves the reasoning unfinished.
Match the editions before buying or revising
The Amendment 4 set is BS 7671:2018+A4:2026, the On-Site Guide 9th edition and Guidance Note 3 10th edition. Check the full designation or edition number on the title page when buying a used copy.
The IET gives 15 October 2026 as the withdrawal date for the previous BS 7671:2018+A2:2022+A3:2024 version. That transition for the standard does not decide which book your booked examination uses: the qualification version does.
Check the publisher’s errata as well as the edition. Keep corrections with your study materials, and ask your assessment centre how any permitted correction should be handled in the examination copy.
Which book can you use in the 2382-26 exam?
For City & Guilds 2382-26, the permitted reference is BS 7671:2018+A4:2026. The On-Site Guide and Guidance Note 3 are not additional permitted books for that assessment. Use the paper reference; electronic copies are not permitted in externally marked examinations.
Practise finding answers in the same permitted book you will use on the day. If you always search a digital copy during revision, include sessions with the paper contents, index and cross-references so the change of format does not consume your exam time.
A sensible order for your next study session
You do not need to read all three books from front to back before a useful revision session. Pick one task and follow it through.
- Preparing for 2382: confirm your qualification version, obtain its permitted BS 7671 edition and practise locating requirements in it.
- Studying a common installation arrangement: read the On-Site Guide’s scope and assumptions, then follow its references back to BS 7671.
- Preparing for inspection and testing: use Guidance Note 3 to connect the purpose of a check, its method and its record; confirm the applicable requirement in BS 7671.
- Reviewing a mistake: write down whether the gap was finding the reference, understanding a condition or interpreting the question. Choose the next exercise to address that gap.
Quick answers
Does the On-Site Guide replace BS 7671?
No. It helps apply BS 7671 within its stated scope. You still need the standard for the full requirements and for situations outside the guide’s assumptions.
Do I need Guidance Note 3 just for the 18th Edition exam?
It can support wider inspection and testing study, but BS 7671 is the permitted reference for City & Guilds 2382-26. Build your exam preparation around that book.
Can I use an older book because its cover says 18th Edition?
Check the full amendment designation. Several versions are called the 18th Edition, and the name alone does not show that the book matches your assessment.