BS 7671 Section by Section: A Revision Breakdown for the 18th Edition Exam

BS 7671:2018+A3:2024 runs to over 700 pages across 8 Parts and 17 Appendices. If you’re preparing for the City & Guilds 2382-22 exam, you don’t have time to give every page equal attention — and you shouldn’t try to. The question weighting is uneven, and understanding where the marks are concentrated is one of the most effective things you can do before you start revising.

 

This guide breaks down every part of BS 7671, tells you what each one covers, how heavily it’s tested, and what to prioritise within it. Think of it as your revision map — so you spend your study hours where they’ll earn you the most marks.

 

If you haven’t already, read our overview of how to pass the 18th Edition exam first time for general exam strategy. This guide goes deeper into the regulations themselves.

The Big Picture — How the Marks Are Spread

Before diving into each part, here’s the approximate question distribution across the 60-question paper:

 

Part	Topic	Questions	% of Exam	Priority
1	Scope & Fundamental Principles	4	7%	Medium
2	Definitions	2	3%	High (underpins everything)
3	General Characteristics	6	10%	Medium–High
4	Protection for Safety	15	25%	Critical
5	Selection & Erection	14	23%	Critical
6	Inspection & Testing	4	7%	Medium–High
7	Special Installations	7	12%	High
8	Prosumers & Appendices	8	13%	Medium–High
	Total	60	100%

 

Key point: Parts 4 and 5 together account for 29 questions — 48% of the paper. Add Parts 3 and 7 and you’re at 42 questions (70%). Your revision time should reflect this weighting.

 

Now let’s look at each part in detail.

 

Part 1 — Scope, Object and Fundamental Principles

Approximate questions: 4 (7%)

 

Part 1 defines what BS 7671 applies to and what it excludes. It’s short, but it sets the foundation for everything that follows.

 

Key Area	What to Know
Scope (Chapter 11)	BS 7671 applies to installations operating at up to 1000V AC. It excludes lightning protection systems, mines and quarries, and equipment on board ships
Exclusions	Know what’s specifically excluded — questions often test the boundaries
Fundamental principles (Chapter 13)	Every installation must be designed, erected, and verified so that it provides protection against electric shock, fire, burns, and overcurrent
Responsibility	The designer, installer, and inspector/tester each carry specific responsibilities

 

Exam tip: Part 1 questions are usually straightforward — they test whether you know the scope and limitations of the regulations. Read this part once carefully and you should pick up the marks without difficulty.

 

Part 2 — Definitions

Approximate questions: 2 (3%)

 

Only 2 direct questions, but Part 2 is far more important than its weighting suggests. Every technical term used across the remaining 6 Parts is defined here. Misunderstand a definition and you’ll cascade into wrong answers on questions about protection, cable selection, and testing.

 

Definitions You Must Know Cold

 

Term	What It Means	Why It Matters
Basic protection	Prevents contact with live parts in normal conditions	Insulation, barriers, enclosures
Fault protection	Ensures disconnection under fault conditions	CPCs, RCDs, overcurrent devices
Exposed-conductive-part	Metal part of equipment, not normally live, that may become live under fault	Drives earthing and bonding requirements
Extraneous-conductive-part	Conductive part not forming part of the installation, liable to introduce a potential	Metal water pipes, structural steelwork
TN-S, TN-C-S, TT	The three earthing systems	Determines RCD requirements, disconnection times, and Zs limits
SELV, PELV, FELV	Extra-low voltage classifications	Each has different earthing and protection requirements

 

Remember: The distinction between exposed-conductive-parts and extraneous-conductive-parts drives bonding requirements throughout Parts 4 and 5. If you confuse these two, you’ll get bonding questions wrong. See our guide on earthing and bonding explained for a detailed breakdown.

 

Part 3 — Assessment of General Characteristics

Approximate questions: 6 (10%)

 

Part 3 covers what you need to know about the supply before you design the installation. It’s the assessment stage — gathering the characteristics of the incoming supply and the conditions in which the installation will operate.

 

Chapter	Topic	What to Revise
31	Purposes, supplies, and structure	Single-source vs multi-source supplies, maximum demand
32	External influences	IP rating codes, temperature ranges, environmental conditions
33	Compatibility	Harmonic currents, voltage disturbances
34	Maintainability	Access for inspection, testing, and maintenance
35	Safety services	Supplies for fire alarm circuits and emergency lighting

 

Exam tip: Chapter 32 (external influences) is a common question source. Know what the IP code digits mean — the first digit is protection against solid objects, the second is protection against water. IP44, IPX4, and IPX7 appear throughout Parts 5 and 7.

 

Part 4 — Protection for Safety

Approximate questions: 15 (25%) — the single most heavily tested part

 

This is where the marks are. Part 4 covers the four types of protection and it’s the densest part of the exam. If you’re going to over-prepare on anything, over-prepare on this.

 

Chapter	Topic	Key Content
41	Protection against electric shock	ADS (automatic disconnection of supply), disconnection times, Zs limits, 30 mA RCD requirements
42	Protection against thermal effects	Fire safety, protection against burns
43	Protection against overcurrent	Overload (Ib ≤ In ≤ Iz), fault current, I2 ≤ 1.45 × Iz
44	Protection against voltage disturbances	Overvoltage protection, SPD requirements (updated in Amendment 3)

 

The Numbers You Must Memorise from Part 4

 

Value	What It Means	Regulation
0.4s	Max disconnection time — TN system, final circuits ≤ 32A	411.3.2.2
5s	Max disconnection time — distribution circuits	411.3.2.3
0.2s	Max disconnection time — TT system, final circuits	411.3.2.4
30 mA	Additional protection by RCD	415.1.1
Ib ≤ In ≤ Iz	Overload coordination rule	433.1

 

Key point: Chapter 41 alone can generate 8–10 questions. Know the disconnection times, when RCDs are required for additional protection (Reg. 415.1), and how to use Table 41.3 for maximum Zs values. For a deeper look, see our Part 4 revision guide.

 

Part 5 — Selection and Erection of Equipment

Approximate questions: 14 (23%)

 

Part 5 is the second-highest weighted part and covers the practical side — choosing cables, wiring systems, protective devices, and switchgear.

 

Chapter	Topic	Key Content
51	Common rules	Selection based on voltage, current, frequency, compatibility
52	Wiring systems	Cable installation methods, grouping factors, thermal insulation
53	Switchgear and controlgear	Isolators, switching devices, coordination
54	Earthing and protective conductors	CPC sizing (Table 54.7), main bonding conductor sizes, earthing arrangements
55	Other equipment	Luminaires, high-voltage discharge lighting, generators
56	Safety services	Circuits for fire safety and emergency systems

 

Key Values from Part 5

 

Value	What It Means	Regulation
3% / 5%	Max voltage drop — 3% for lighting circuits, 5% for all others	525
6 mm² Cu	Minimum main protective bonding conductor (TN system, 25 mm² supply)	544.1
Table 54.7	Minimum CPC sizes based on line conductor cross-section	543.1

 

Exam tip: Cable sizing questions often link Part 5 with Part 4 — you need to select a cable that satisfies both overload protection (Part 4) and voltage drop limits (Part 5). Our guide on cable size calculation and protective device rating walks through the full procedure.

 

Part 6 — Inspection and Testing

Approximate questions: 4 (7%)

 

Only 4 questions, but they’re among the most predictable in the exam. The testing sequence from Regulation 612 appears almost every sitting.

 

Key Area	What to Know
Chapter 61	Initial verification must include visual inspection (Reg. 611) followed by testing (Reg. 612)
Chapter 62	Periodic inspection and testing — intervals, condition report coding (C1, C2, C3, FI)
Chapter 63	Certification — EIC for new work, MEIWC for additions/alterations, EICR for periodic inspection

 

The Testing Sequence (Reg. 612)

 

Order	Test	Type
1	Continuity of protective conductors	Dead
2	Continuity of ring final circuit conductors	Dead
3	Insulation resistance (500V DC, min 1.0 MΩ)	Dead
4	SELV and PELV verification	Dead
5	Polarity	Dead
6	Earth electrode resistance	Dead
7	Earth fault loop impedance (Zs)	Live
8	Additional protection — RCD testing	Live
9	Prospective fault current (Ipf)	Live
10	Phase sequence	Live
11	Functional testing	Live
12	Voltage drop	Live

 

Remember: Dead tests always come before live tests — you don’t energise the circuit until you’ve confirmed it’s electrically sound. Learn this sequence in order. It’s near-guaranteed marks.

 

Part 7 — Special Installations or Locations

Approximate questions: 7 (12%)

 

Part 7 contains individual sections for locations that present increased risk. You can’t learn all of them in depth, but five sections account for the vast majority of questions:

 

Section	Location	Key Requirement
701	Bathrooms	Zone system (0, 1, 2), 30 mA RCD on all circuits, IP ratings per zone
704	Construction sites	110V centre-tapped (55V to earth), 30 mA RCD ≤ 32A, 3-monthly inspection
712	Solar PV	DC side live during daylight, labelling requirements, string isolation
722	EV charging	Dedicated circuit, Type A RCD minimum, continuous duty rating
801/802	Prosumers	Anti-islanding (Reg. 802.4), labelling at all isolation points

 

Important: Part 7 requirements supplement the general rules in Parts 1–6 — they don’t replace them. A bathroom installation must comply with all of Part 4 and Section 701’s additional requirements. Exam questions frequently test whether you understand this relationship.

 

Part 8 — Prosumers Installation

Approximate questions: 3–4 (within the “Part 8 & Appendices” allocation)

 

Part 8 was introduced in Amendment 2 and covers installations where the consumer also generates electricity — solar PV systems, battery storage, wind turbines, or any combination of these. Amendment 3 updated several requirements.

 

Chapter	Topic	Key Content
801	General requirements	Labelling requirements, safety at every point of isolation
802	Sources of supply	Anti-islanding protection, switching and isolation for on-site generators

 

Exam tip: Part 8 is short — about 20 pages. It’s worth reading in full because questions tend to test the specific requirements (anti-islanding, labelling) rather than broad principles. Straightforward marks if you’ve read the text.

 

The Appendices — Your Practical Reference

The Appendices carry roughly 4–5 questions and contain the data tables you’ll use both in the exam and on site. Three are critical:

 

Appendix	Content	When You’ll Use It
3	Adiabatic equation and k values	CPC sizing verification — k = 115 for Cu/PVC is one to memorise
4	Current-carrying capacity tables	Cable selection — rating factors for grouping, ambient temperature, thermal insulation
14	Maximum Zs values	Quick-reference alternative to Table 41.3 — used for verification

 

Tab these in your copy of BS 7671 before the exam. You will need to look up specific values from these appendices under time pressure.

 

Putting It Together — A Priority-Based Revision Order

Based on the mark weighting and the predictability of questions, here’s a suggested revision order:

 

Priority	Part(s)	Reason
1st	Part 4	25% of marks — the single most heavily tested part
2nd	Part 5	23% of marks — cable sizing, voltage drop, CPC sizing
3rd	Part 7	12% of marks — learn the big five special locations
4th	Part 2 + Part 3	Part 2 underpins all other questions; Part 3 carries 10%
5th	Part 6	Testing sequence is near-guaranteed marks
6th	Part 8 + Appendices	Short enough to read in full; predictable questions
7th	Part 1	Important but low question count — one careful read is usually sufficient

 

Key point: This isn’t a suggestion to skip anything. It’s a guide to where your time will have the most impact. If you’re consistently scoring well on Parts 4 and 5 in practice tests, shift your focus to the parts where you’re still dropping marks. For a realistic timeline, see our guide on how long to study for the 18th Edition.

 

Practice and Further Study

Understanding the structure of BS 7671 is only the first step — you need to test yourself under exam conditions. Try our topic-specific quizzes to identify where your weak spots are:

• Part 4 — Protection for Safety quiz
• Part 5 — Selection and Erection of Equipment quiz
• Part 6 — Inspection and Testing quiz
• Part 7 — Special Installations quiz

 

Our app includes 580+ practice questions covering all 8 Parts of BS 7671 with detailed explanations referencing specific regulation numbers, plus full timed mock exams that mirror the real exam’s weighted question distribution — so you practise on the parts that carry the most marks.

 

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