What is the difference between the 2391-50, 2391-51, and 2391-52?

The C&G 2391 qualification comes in three variants: 2391-52 (the current combined qualification covering both Initial Verification and Periodic Inspection and Testing). The 2391-52 replaced the earlier 2391-51, which was itself a combined qualification that replaced the older separate qualifications: the C&G 2394 (Initial Verification) and C&G 2395 (Periodic Inspection and Testing). Most electricians take the 2391-52 as it covers both scopes and is the most widely recognised by employers and competent person schemes. The exams for each variant are similar in format but the questions and practical scenarios differ based on the scope.

How hard is the 2391 compared to the 18th Edition?

The 2391 is generally considered harder than the 18th Edition (C&G 2382) because it requires both theoretical knowledge and practical competence. The written exam is more demanding — instead of multiple-choice questions, you must write detailed short answers with regulation references. The practical assessment adds another dimension: you must physically carry out an inspection and test sequence on a real or simulated installation, record the results on the correct forms, and produce a completed EICR or EIC. Many candidates who comfortably pass the 18th Edition fail the 2391 on their first attempt, particularly the practical assessment. The key differences are: longer, more detailed answers required; need to demonstrate hands-on testing competence; must complete certification paperwork accurately; and the overall pass rate is lower (typically 55 to 65% compared to 65 to 75% for the 2382).

What instruments do I need for the 2391 practical assessment?

For the practical assessment, you typically need a multifunction tester (MFT) that can perform continuity testing, insulation resistance testing, earth fault loop impedance measurement, prospective fault current measurement, and RCD testing. The most commonly used models are the Megger MFT1741 or MFT1835, Fluke 1664FC, Metrel MI3155, or Kewtech KT66DL. You will also need a proving unit or voltage indicator (such as a Fluke T150 or Kewtech KT1780) for safe isolation. Some centres provide instruments; others require you to bring your own. Check with your centre beforehand. Your instruments must be within their calibration date — bring the calibration certificates. You should also bring test leads, probes, and any adaptors you might need. Practise with your own instruments before the exam so you are comfortable with the controls and can operate them quickly.

What does the 2391 practical assessment involve?

The practical assessment requires you to carry out an inspection and test of an electrical installation (real or simulated). You will need to: (1) Carry out a safe isolation procedure before any dead testing. (2) Perform the full test sequence in the correct order: continuity of protective conductors (R1+R2), continuity of ring final circuit conductors, insulation resistance, polarity (if not confirmed by continuity testing), earth fault loop impedance (Zs), prospective fault current (PSCC), and RCD testing (trip time and trip current). (3) Carry out a visual inspection, checking for compliance with BS 7671 — looking for defects such as missing earth labels, incorrect IP ratings, damaged accessories, or non-compliant installations. (4) Record all results on the appropriate test forms (Schedule of Test Results). (5) Complete the certification — either an EIC (for initial verification) or an EICR (for periodic inspection), including observations and the overall assessment. (6) The examiner will also ask you oral questions during or after the assessment to verify your understanding.

How long does it take to complete the 2391 qualification?

Most classroom-based 2391 courses run over 1 to 2 weeks (5 to 10 days), combining theory lessons with practical workshop sessions. Distance learning options typically give you 6 to 12 months to complete, with a practical assessment day booked at a centre. The total study time depends on your starting knowledge: if you already hold the 18th Edition qualification and have practical testing experience, a 1-week intensive course may be sufficient. If you are newer to inspection and testing, a 2-week course with additional self-study is more realistic. You should also allow time for practice — ideally, do some inspection and testing work on real installations (under supervision if you are not yet qualified) before the assessment. Elec-Mate's inspection and testing course lets you study the theory at your own pace, practise with mock exams, and use the EPA simulator to rehearse the practical elements.

Can I retake the 2391 if I fail?

Yes, you can retake either or both components of the 2391 if you fail. If you pass the written exam but fail the practical (or vice versa), you only need to retake the component you failed — you do not need to redo both. The retake fee varies by centre but is typically £100 to £200 per component. Most centres allow retakes within 6 to 12 months of the original attempt. If you fail the practical assessment, ask the examiner for feedback on what you did wrong — they should be able to tell you which areas cost you marks. Common reasons for practical failure include: performing tests out of sequence, recording results inaccurately, failing to carry out safe isolation correctly, missing obvious visual defects, or not completing the certification paperwork fully. Address these specific areas before your retake.

EXAM GUIDE

2391 Exam Tips: How to Pass Inspection & Testing

The C&G 2391 is the qualification every electrician needs for inspection and testing work. It has a written exam and a practical assessment — and the pass rate is lower than the 18th Edition. This guide covers both components, the test sequence you must know, and the mistakes that cost candidates marks.

Start 7-day free trial

Free for 7 days · No charge until day 8 · Cancel anytime · Used by 1,000+ UK electricians

11 min readUpdated 2026-06-10Andrew Moore, Founder of Elec-Mate

Written and reviewed by Andrew Moore, founder of Elec-Mate, against BS 7671:2018+A4:2026, IET Guidance Note 3 and the IET On-Site Guide.

ShareX in W

1,000+

UK electricians

“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”

Daniel Palmer — DP Electrical

Key Takeaways

1The C&G 2391 has two components: a 2-hour written exam (40 short-answer questions) and a practical assessment where you inspect and test a real or simulated installation.
2The correct test sequence is critical — continuity, insulation resistance, polarity, earth fault loop impedance, prospective fault current, then RCD testing. Examiners will fail you for testing out of order.
3Know GN3 (Guidance Note 3: Inspection & Testing) as well as BS 7671 — the practical assessment is based heavily on the GN3 procedures.
4The written exam expects detailed, technical answers with regulation references — one-word answers will not score marks.
5Elec-Mate offers a dedicated inspection and testing course with mock exams, flashcards, and the EPA simulator to prepare you for the practical assessment.

01 · Exam Guide

What Is the C&G 2391 Qualification?

The City & Guilds 2391 (Inspection and Testing of Electrical Installations) is the industry-standard qualification for electricians who carry out inspection, testing, and certification of electrical installations in the UK. It proves you can inspect and test both new installations (initial verification) and existing installations (periodic inspection), and produce the correct certification — EIC, EICR, and Minor Works Certificates.

The 2391 is a requirement for most competent person scheme registrations (NICEIC, NAPIT, ELECSA) and is expected by employers across the trade. Without it, you cannot independently sign off inspection and testing work. It sits alongside the 18th Edition qualification (C&G 2382) — you need both to be considered fully qualified for inspection work.

The qualification is assessed through two components: a written exam and a practical assessment. Both must be passed to achieve the full qualification.

Free download

Get the BS 7671 A4:2026 Cheat Sheet — free

Every key change in the 2026 amendment on one page. AFDDs, TN-C-S protection, new schedule columns, model forms. Pinned on your van dash.

Every regulation change summarised
New model forms (EIC + MEIWC)
Free PDF — no subscription

02 · Exam Guide

Written Exam Format and What to Expect

The 2391 written exam is significantly different from the 18th Edition multiple-choice exam. Here is what you are facing:

40 short-answer questions in 2 hours. These are not multiple-choice — you must write out your answers in full sentences with technical detail and regulation references.
Open-book — you can bring BS 7671 and GN3 (Guidance Note 3: Inspection & Testing). Both can be tabbed. This is different from the 2382 exam where only BS 7671 is permitted.
Pass mark: 60%. With 40 questions, you need to score at least 24 correct answers. Each question may carry different marks depending on complexity.
Regulation references are expected. An answer of "you need RCD protection" will score fewer marks than "Regulation 411.3.3 requires additional protection by an RCD with a rated residual operating current not exceeding 30mA."

The written exam covers: the purpose and scope of inspection and testing; the difference between initial verification and periodic inspection; the correct test sequence and why the order matters; interpretation of test results; classification of observations (C1, C2, C3, FI); completion of certification paperwork; and the legal framework including the Electricity at Work Regulations 1989 and the Health and Safety at Work Act 1974.

03 · Exam Guide

Practical Assessment: What You Must Demonstrate

The practical assessment is where many candidates struggle. You are given a real or simulated electrical installation and must carry out a complete inspection and test. The examiner watches you work and assesses your competence against specific criteria.

Safe Isolation

You must demonstrate the safe isolation procedure correctly: prove dead using a voltage indicator, lock off, prove the voltage indicator still works. Failing to do this correctly can result in an automatic fail — it is a safety-critical procedure.

Visual Inspection

Carry out a thorough visual inspection of the installation. Check for: correct labelling, presence of safety notices, condition of accessories, adequacy of connections, correct IP ratings, cable condition, and compliance with BS 7671. The examiner expects you to identify deliberate defects placed in the installation.

Testing Sequence

Perform all tests in the correct order (see next section). Record every result accurately on the Schedule of Test Results. The examiner will check that you are using instruments correctly, connecting probes to the right terminals, and reading results accurately.

Certification

Complete the full certification paperwork — EIC or EICR as appropriate. This includes the schedule of test results, the schedule of inspections, observations with correct classification codes, and the overall assessment (Satisfactory or Unsatisfactory). Missing fields or incorrect classification codes will cost marks.

Free C&G 2391 mock exam — 300-question bank

Sit a free 2391 Inspection & Testing mock exam now: 30 random questions from a 300-question bank, 90-minute timer. Covers initial verification, periodic inspection, EICR coding, RCD testing, GN3 procedures. No sign-up.

Start the 2391 mock exam →

04 · Exam Guide

Common Pitfalls That Cost Candidates Marks

Examiners report the same mistakes appearing year after year. Avoid these and you will be ahead of most candidates:

Testing out of sequence. The test sequence exists for safety and accuracy reasons. If you perform earth fault loop impedance before insulation resistance testing, you could be testing a circuit with a fault and get inaccurate results — or worse, create a dangerous condition. The examiner will fail you for this.
Skipping safe isolation or doing it incorrectly. Forgetting to prove the voltage indicator works after proving dead, or not locking off, are common mistakes. Some candidates prove dead at the consumer unit but not at the point of work.
Not recording results accurately. Writing "pass" instead of the actual measured value. The Schedule of Test Results requires numerical values — for example, "0.32 ohms" for R1+R2, not "pass." The examiner needs to see that you actually measured and recorded the result.
Incorrect observation codes. Classifying a C2 (Potentially Dangerous) defect as C3 (Improvement Recommended) or vice versa. Know the definitions: C1 = immediate danger, C2 = not immediately dangerous but could become so, C3 = does not comply with current standard but not dangerous.
Incomplete certification. Leaving sections of the EIC or EICR blank. Every field must be completed — if a field does not apply, write "N/A" rather than leaving it empty. Missing signatures, dates, or the next inspection date are common omissions.

Practise with unlimited mock exams

AI-generated mocks, instant marking, and explanations on every question — targeted at your weakest topics. From £6.99/mo.

Start practising free

05 · Exam Guide

The Test Sequence You Must Know

The correct test sequence for the 2391 is set out in GN3 (Guidance Note 3: Inspection & Testing) and referenced in Part 6 of BS 7671. You must perform tests in this order because each test depends on the results of the previous one:

Continuity of protective conductors (R1+R2) — confirms the earth path is continuous. If this fails, there is no point testing earth fault loop impedance later.
Continuity of ring final circuit conductors — confirms the ring is complete and not broken or cross-connected. Measures R1, Rn, and R2 for each ring.
Insulation resistance — tests for breakdown between live conductors and earth. Must be done with the supply isolated (dead test). Minimum acceptable value: 1 megohm at 500V DC for most circuits.
Polarity — confirms line, neutral, and earth are connected correctly at every point. Often confirmed as part of the R1+R2 continuity test.
Earth fault loop impedance (Zs) — measures the impedance of the earth fault path. The measured value must be less than the maximum permitted Zs from the tables in Appendix 3 of BS 7671 (after applying the 0.8 correction factor).
Prospective fault current (PSCC/PEFC) — measures the maximum current that would flow under fault conditions. The protective device must be capable of breaking this current.
RCD testing — tests the trip time at rated current (should trip within 300ms for general-purpose RCDs, 40ms at 5x rated current for additional protection RCDs) and the trip current (should not trip at 50% of rated current).

For periodic inspection, you may also need to carry out additional tests such as earth electrode resistance testing (for TT systems) and functional testing of switchgear and controls. The key principle is: dead tests first (with the supply off), then live tests (with the supply on), in the order listed above.

06 · Exam Guide

Preparation Strategy for Both Components

Passing the 2391 requires preparation for both the written exam and the practical assessment. Here is how to approach each:

Written Exam Preparation

Study both BS 7671 and GN3. The written exam draws heavily from both. GN3 covers the practical aspects of inspection and testing — test methods, instrument requirements, and result interpretation.
Practise writing detailed answers. Unlike the 2382 multiple-choice exam, the 2391 expects full technical answers. Practise writing answers to past questions, including regulation references.
Use flashcards for key regulations. Elec-Mate's flashcards tool covers the regulations most commonly tested in the 2391 written exam. Spaced repetition helps you recall regulation numbers under exam pressure.

Practical Assessment Preparation

Practise on real installations. If possible, carry out inspection and testing on real installations under supervision. The more you practise the physical process of connecting instruments and recording results, the more confident you will be on assessment day.
Memorise the test sequence. You should be able to recite the test sequence in your sleep. Practise it until it is automatic — on assessment day, nerves can make you forget things you normally know.
Practise filling in certification. Complete blank EIC and EICR forms multiple times. Know which fields go where, what format the results should be in, and how to classify observations correctly.

Study for the 2391 with Elec-Mate

Elec-Mate's inspection and testing course covers every topic on the 2391 syllabus. Flashcards for regulation recall, mock exams for the written paper…

Try it free for 7 days

07 · Exam Guide

Exam Day Tips

On the day of your 2391 exam, small details can make the difference between pass and fail. Here is what to remember:

Written exam: Allocate your time across all 40 questions. Do not spend too long on any single question. If you are stuck, move on and come back. Write clearly and include regulation references wherever possible — even a partial answer with the correct regulation number can score marks.
Practical assessment: Talk the examiner through what you are doing and why. If you explain "I am now carrying out insulation resistance testing at 500 volts DC between line and earth, because I need to confirm there is no breakdown of insulation before I energise the circuit," the examiner knows you understand the process — even if your instrument technique is not perfect.
Bring everything you need: BS 7671 (tabbed), GN3 (tabbed), photo ID, instruments (calibrated), test leads, proving unit, PPE, pen, and spare pen. Arrive 15 minutes early.
Stay calm during the practical. Being watched by an examiner is stressful. Take a breath, work methodically through the test sequence, and do not rush. A steady, confident approach scores better than a frantic one.

Frequently Asked Questions About the 2391 Exam

What electricians say

Verified reviews from the UK App Store.

One App for Everything!

Elec-Mate is my go to app for business and electrical work. It's feature rich without feeling cluttered. A true all in one app for quotes, certs, calculations, RAMS, EICRs, and more. I use it every day without fail, and it makes my workflow much smoother since I'm not jumping between apps anymore. The price-to-feature ratio is excellent. Any issues I've had, the developer responds within the hour and usually fixes them the same day. 100% recommend.

Fantastic app for electricians

I've used the app and the web based version for a while now and it's well worth the investment. If you're an apprentice or experienced Spark give it a go, you won't be disappointed.

Absolutely amazing

I've been using Elec-Mate for a while now, and honestly, it's one of the best apps I've ever downloaded. Every aspect of it feels thoughtfully designed, from the clean and intuitive interface to the powerful features that make everything so easy to manage. It's clear that a lot of care and attention went into building this app, and it shows in every detail.

Trusted by electricians across the UK

Real feedback from real sparks

“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”

Daniel Palmer

Sole Trader · DP Electrical

“I've won two contracts this month because I could turn quotes around same-day with the AI cost engineer.”

Nathan Perry

Electrician · NP Electrical Services

“The study centre got me through my AM2. Mock exams and flashcards are brilliant.”

Jake Pizey

3rd Year Apprentice · Apprentice

7-Day Free Trial — Cancel Anytime, No Hassle

Prepare for the 2391 with Elec-Mate

Structured inspection and testing course, flashcards, timed mock exams, and EPA simulator. 46+ training courses covering every electrical qualification. 7-day free trial, cancel anytime.

“Replaced three separate apps with Elec-Mate. Certs, quotes, and scheduling all in one place.”

Daniel Palmer, DP Electrical

From £6.99/mo after trial — less than a coffee a week

or download the app

7 days free, then from £6.99/moCancel in one tap — no calls, no hassleiOS, Android & WebBS 7671 compliant

2391 Exam Tips: How to Pass Inspection & Testing

Key Takeaways

What Is the C&G 2391 Qualification?

Get the BS 7671 A4:2026 Cheat Sheet — free

Written Exam Format and What to Expect

Practical Assessment: What You Must Demonstrate

Safe Isolation

Visual Inspection

Testing Sequence

Certification

Free C&G 2391 mock exam — 300-question bank

Common Pitfalls That Cost Candidates Marks

Practise with unlimited mock exams

The Test Sequence You Must Know

Preparation Strategy for Both Components

Written Exam Preparation

Practical Assessment Preparation

Study for the 2391 with Elec-Mate

Exam Day Tips

Frequently Asked Questions About the 2391 Exam

What is the difference between the 2391-50, 2391-51, and 2391-52?

How hard is the 2391 compared to the 18th Edition?

What instruments do I need for the 2391 practical assessment?

What does the 2391 practical assessment involve?

How long does it take to complete the 2391 qualification?

Can I retake the 2391 if I fail?

Continue reading

18th Edition Exam Tips

Testing Sequence Guide

Insulation Resistance Testing

Study Tips for Electricians

How to Fill In an EICR

Inspection & Testing Course

What electricians say

One App for Everything!

Fantastic app for electricians

Absolutely amazing

Trusted by electricians across the UK

Prepare for the 2391 with Elec-Mate