UNIT REVISION

City & Guilds 2357 Unit 399: Electrotechnical occupational competence (ELT OC1) — Complete Revision Guide

A structured revision walkthrough of every topic in City & Guilds 2357 Unit 399 (Electrotechnical occupational competence (ELT OC1)). Use it as a personal study checklist — work through each topic, tick off the points you can confidently explain or calculate, and use the linked Elec-Mate tools to practice the calculation-led parts. Designed for apprentices working through an NVQ pathway with on-the-job portfolio evidence.

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12 min readUpdated 2026-05-18Andrew 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.

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Key Takeaways

  • 1City & Guilds 2357 Unit 399 — Electrotechnical occupational competence (ELT OC1) — is a core component of the Level 3 NVQ Diploma in Installing Electrotechnical Systems and Equipment.
  • 2This unit is typically delivered to apprentices working through an NVQ pathway with on-the-job portfolio evidence and covers 8 main topic areas.
  • 3Across the 8 topics there are 29 specific points you should be able to explain, demonstrate or calculate before the end-of-unit assessment.
  • 4Common assessment formats include online multiple-choice exams, written short-answer papers, and practical workshop tasks observed by your tutor.
  • 5Use the structured topic list below as a personal checklist — work through each point and confirm you can explain it without referring to your notes.
  • 6The Elec-Mate apprentice tier includes mock exams, flashcards, and revision notes mapped to this unit. Use the tools to test yourself between college blocks and on-site days.
01 · Unit Revision

Topic 1: How to interpret specifications, drawings and diagrams

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • Interpret specifications and technical data for the installation of: • protective earthing systems • a ring final circuit • a general lighting circuit • a control system for a three-phase motor • a central heating/sustainable energy system • a safety service circuit • a data cabling system • a three-phase socket-outlet. Unit 399 Electrotechnical occupational competence (ELT OC1).
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02 · Unit Revision

Topic 2: How to undertake risk assessments

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • Review safe working practices.
  • Undertake a risk assessment.
  • Complete risk assessment documentation in accordance with organisational procedures. 214 City & Guilds Level 3 Diplomas in Electrotechnical Technology (2357) Unit 399 Electrotechnical occupational competence (ELT OC1).
03 · Unit Revision

Topic 3: How to carry out the safe isolation of electrical circuits and complete electrical installations

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • Locate correct means of isolation.
  • Follow correct procedures for the isolation of electrical circuit(s) and complete electrical installations.
  • Isolate circuit (s) in correct sequence.
  • Select correct test and measuring instruments.
  • Correctly test for the presence of an electrical supply. Unit 399 Electrotechnical occupational competence (ELT OC1).
04 · Unit Revision

Topic 4: How to plan and prepare to install, terminate and connect wiring systems

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • In accordance with an installation specification select the correct cables, accessories, equipment, components and protective devices for the installation of: • protective earthing systems • a ring final circuit • a general lighting circuit • the control of a three-phase motor • a central heating/sustainable energy system • a safety service circuit • a data cabling system • a three-phase socket-outlet. 216 City & Guilds Level 3 Diplomas in Electrotechnical Technology (2357) Unit 399 Electrotechnical occupational competence (ELT OC1).
05 · Unit Revision

Topic 5: How to complete the installation, termination and connection of wiring systems in accordance with industry requirements

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • In accordance with an installation specification install, terminate and connect cables, accessories, equipment, components and protective devices for the installation of: • protective earthing systems • a ring final circuit • a general lighting circuit • the control of a three-phase motor • a central heating/sustainable energy system • a safety service circuit • a data cabling system • a three-phase socket-outlet. Unit 399 Electrotechnical occupational competence (ELT OC1).

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06 · Unit Revision

Topic 6: How to complete the visual inspection, initial verification and certification of an electrical installation

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • Comply with correct procedures.
  • Record relevant findings on correct documentation. 218 City & Guilds Level 3 Diplomas in Electrotechnical Technology (2357) Unit 399 Electrotechnical occupational competence (ELT OC1).
07 · Unit Revision

Topic 7: How to complete the testing and certification of an electrical installation in accordance with industry requirements

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • Select and use the correct measuring instruments.
  • Complete the correct documentation in accordance with statutory and non-statutory regulations. Unit 399 Electrotechnical occupational competence (ELT OC1).
  • Confirm instruments function accurately.
  • Measure the continuity of protective conductors.
  • Measure the continuity of ring final circuit conductors.
  • Measure the insulation resistance of the installation and its circuits.
  • Confirm the polarity of the installation’s electrical outlets and components.
  • Determine the installation’s Earth Fault-Loop Impedance (EFLI).
  • Determine the installation’s Prospective Fault Current (PFC).
  • Carry out functional tests on the installation’s equipment and components.
08 · Unit Revision

Topic 8: How to diagnose, and recommend how to rectify, electrical faults in an electrical installation in accordance with industry requirements

In this section you should be confident with the following points. Each one is a specific topic you should be able to explain, demonstrate, or calculate.

  • Undertake an assessment of risk accordingly.
  • Carry out safe isolation in the correct sequence as appropriate to fault diagnosis procedures.
  • Select and use correctly, fit for purpose tools, equipment and instruments.
  • Carry out relevant checks and preparations.
  • Locate faults from given information.
  • State how the identified faults can be rectified. 220 City & Guilds Level 3 Diplomas in Electrotechnical Technology (2357) Unit 399 Electrotechnical occupational competence (ELT OC1) Notes for guidance To undertake this unit, learners must provide auditable formal evidence that they have the relevant electrotechnical knowledge, understanding, experience and skills at the appropriate level that enables them to carry out the assessment activities effectively and safely as prescribed for each learning outcome. This unit must only be assessed in a National Electrotechnical Training (NET) approved centre. All criteria set by NET must be met full and continuously for each assessment. NET, rather than City & Guilds, should be contacted regarding any queries regarding the delivery and/or assessment for this unit (2357-399). As with all assessments, the candidate’s result for this unit must be submitted to City & Guilds on the Walled Garden to allow for certification. Appendix 1 Relationships to other qualifications Links to other qualifications and frameworks These qualifications will be contained within the SummitSkills Apprenticeship framework. Please visit SummitSkills website www.summitskills.org.uk for more details. candidates to progress onto upon completion of these qualifications. Please see the Progression Opportunities (section 1.2 of this handbook) for more details. These qualifications have connections to the following within the electrical suite offered by City & Guilds: • 2382 • 2391 2382 Requirements for Electrical Installations 17th Edition (BS7671: 2008 (2015)) To gain certification for Level 3 Award in the Requirements for Electrical Installations BS7671: 2008 (2015), candidates must have achieved the assessment 5357-006 and have been certificated against either 2357-13, 2357-44, 2357-46 or 2357-91. Centres can then register candidates onto the 2382-73 and claim the certification module 2382-902 which will generate this certificate. 18th Edition (BS7671: 2018) To gain certification for Level 3 Award in the Requirements for Electrical Installations BS 7671:2018, candidates must have achieved the assessment 2357-018 (BS7671 2018) and 2357-705 or 2357-725 and have been certificated 2357-13, 2357-44, 2357-46 or 2357-91. Centres can then register candidates onto the 2382-78 and claim the certification module 2382-918 which will generate this certificate. 18th Edition Amendment 2 (BS7671: 2018 (2022)) To gain certification for City & Guilds Level 3 Award in the Requirements for Electrical Installations BS 7671:2018 (2022), candidates must have achieved the assessment 2357-022 (BS7671 2018 (2022)) and 2357-705 or 2357-725 and have been certificated against 2357- 13, 2357-44, 2357-46 or 2357-91. Centres can then register candidates onto the 2382-82 and claim the certification module 2382-922 which will generate this certificate. 222 City & Guilds Level 3 Diplomas in Electrotechnical Technology (2357) 2391 Electrical Inspection and Testing To gain certification for Level 3 Award in Initial Verification of Electrical Installations, candidates must have achieved the assessments 2357-107 and 2357-607 and have been certificated against 2357-13, 2357-34, 2357-35 or 2357-91. Centres can then register candidates onto 2391-71 and claim the certification module 2391- 901 which will generate this certificate. Literacy, language, numeracy and ICT skills development These qualifications includes opportunities to develop and practise many of the skills and techniques required for success in the following qualifications: • Functional Skills (England) – see www.cityandguilds.com/functionalskills • Essential Skills (Northern Ireland) – see www.cityandguilds.com/essentialskillsni • Essential Skills Wales – see www.cityandguilds.com/esw Appendix 2 Sources of general information The following documents contain essential information for centres delivering City & Guilds qualifications. They should be referred to in conjunction with this handbook. To download the documents and to find other useful documents, go to the Centre Document Library on www.cityandguilds.com or click on the links below: Quality Assurance Standards: Centre Handbook This document is for all approved centres and provides guidance to support their delivery of our qualifications. It includes information on • Centre quality assurance criteria and monitoring activities • Administration and assessment systems • Centre-facing support teams at City & Guilds / ILM • Centre quality assurance roles and responsibilities. The Centre Handbook should be used to ensure compliance with the terms and conditions of the Centre Contract. Quality Assurance Standards: Centre Assessment This document sets out the minimum common quality assurance requirements for our regulated and non-regulated qualifications that feature centre assessed components. Specific guidance will also be included in relevant qualification handbooks and/or assessment documentation. It incorporates our expectations for centre internal quality assurance and the external quality assurance methods we use to ensure that assessment standards are met and upheld. It also details the.
09 · Unit Revision

Study This Unit with Elec-Mate

Elec-Mate’s apprentice tier turns this unit checklist into an active study plan. You get mock exam questions, flashcards, and revision notes mapped to this unit, plus working calculators for every calculation-led topic. Most apprentices use the app between college blocks and on the train to site — short bursts of revision compound across the year.

For apprentices

The Elec-Mate apprentice tier includes mock exams, flashcards, and revision notes for City & Guilds 2357 Unit 399 plus every other unit in your qualification. 7-day free trial — see your progress on the tutor dashboard.

A Five-Step Revision Plan for This Unit

A repeatable approach that works for City & Guilds 2357 Unit 399 and every other unit in your qualification.

1

Read through every topic point once

Start at Topic 1 and read every bullet point. Don’t try to memorise — just get familiar with the scope. Note any topic that feels unfamiliar so you can come back to it.

2

Map each topic to its calculator or guide

For calculation-led topics, open the relevant Elec-Mate calculator and try one worked example. For theory-led topics, find the matching section in BS 7671 or the IET On-Site Guide.

3

Work through Elec-Mate mock exam questions

The Elec-Mate apprentice tier includes mock questions mapped to this unit. Aim for 80%+ on a clean run before the real exam.

4

Get hands-on time on the bench

For practical units (inspection and testing, installation), ask your tutor for additional workshop access. The bench is where the points click.

5

Self-explain each topic to a peer

If you can explain a topic in your own words to another apprentice and they understand it, you know it. This is the single highest-leverage revision tactic.

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