UNIT REVISION

City & Guilds 2365-03 Unit 305: Electrical Systems Design — Complete Revision Guide

A structured revision walkthrough of every topic in City & Guilds 2365-03 Unit 305 (Electrical Systems Design). 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 2nd to 4th-year apprentices.

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18 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 2365-03 Unit 305 — Electrical Systems Design — is a core component of the Level 3 Diploma in Electrical Installations.
  • 2This unit is typically delivered to 2nd to 4th-year apprentices and covers 8 main topic areas.
  • 3Across the 8 topics there are 46 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 prepare for the installation of 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.

  • Describe how to plan and implement work allocations, duties of operatives, and coordination with other services and personnel.
  • Identify relevant sources of information which will inform electrical work.
  • Describe the actions required to ensure that electrical work sites are correctly prepared in terms of Health and Safety.
  • State why it is important to check for any pre-existing damage to customer/client property.
  • Explain how to check for any pre-existing damage to customer/client property including equipment, components, building decor and floor finishes.
  • State the actions that should be taken if pre-existing damage to customer/client property is identified.
  • Specify methods for protecting the fabric and structure of the property before and during electrical work.
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02 · Unit Revision

Topic 2: The applications of 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.

  • Explain the constructional features, applications, advantages and limitations of electrical cables.
  • Explain the characteristics of containment, support and wiring systems used in electrical installations.
  • Determine the size of conduit and trunking as appropriate to the size and number of cables.
  • Describe the factors which affect the selection of wiring systems, associated equipment and enclosures.
  • Assess and select suitable wiring systems and equipment appropriate to the situation and use.
03 · Unit Revision

Topic 3: The practices and procedures for carrying out electrical work

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.

  • State the procedures for selecting and safely using appropriate hand tools, power tools and adhesives.
  • State the procedures for selecting and safely using equipment for measuring and marking out.
  • State the criteria for selecting and safely using tools and equipment for fixing and installing wiring systems.
  • State the criteria for selecting and safely using fixing devices for wiring systems.
  • Assess and specify the installation methods to ensure wiring systems are securely fixed, mechanical integrity is maintained, and no damage has occurred.
  • Specify methods and techniques for restoring the building fabric.
04 · Unit Revision

Topic 4: The characteristics and applications of supply systems and consumer equipment

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.

  • Explain the characteristics and applications of earthing arrangements.
  • Explain the characteristics and applications of supply systems.
  • Specify the arrangements for electrical installations regarding isolation and switching, overcurrent protection, and earth fault protection.
05 · Unit Revision

Topic 5: Earthing and protection

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.

  • Explain the purpose of earthing and protective conductors.
  • Identify extraneous and exposed conductive parts.
  • Describe the requirements and measures for protection against electric shock.
  • State the maximum disconnection time for different types of circuit.
  • Explain the earth fault loop path and earth fault loop impedance.
  • Specify requirements and applications of functional earthing.
  • Select suitably sized protective conductors in accordance with BS 7671.

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06 · Unit Revision

Topic 6: Protection against overcurrent

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.

  • Identify types of and reasons for overcurrent.
  • Explain the operating principles, applications and limitations of protective devices.
  • Identify fault current capacities of devices.
  • Outline the need for discrimination between protective devices.
07 · Unit Revision

Topic 7: Electrical systems and circuits

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.

  • Describe the characteristics of standard electrical circuits.
  • Outline the key characteristics and applications of particular electrical systems and circuits.
08 · Unit Revision

Topic 8: The electrical design procedure

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.

  • State the purpose of diversity factors.
  • Verify if the disconnection times have been achieved.
  • Evaluate thermal constraints.
  • Interpret the requirements of sources of information in the design of an installation.
  • Select suitable current using equipment giving consideration to energy efficiency and sustainability.
  • Determine the maximum demand of an installation after the application of diversity.
  • Determine the design current.
  • Select a suitably rated protective device.
  • Establish the installation method reference.
  • Determine appropriate rating factors.
  • Determine the minimum cross-sectional area of live conductors taking into consideration current carrying capacity and voltage drop.
  • Establish if the voltage drop is acceptable.
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 2365-03 Unit 305 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 2365-03 Unit 305 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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