Electrical Systems Design

Assessment Overview

Candidates must successfully complete one design-based task to achieve this assignment. In addition, candidates must complete the 2365-625 e-volve test.

Task A Design Project

Time Allowed

There are no formal time constraints, although the estimated completion time is approximately 20 hours.

Task Instructions

To achieve this assignment, candidates must complete a 10-question design task.

Candidates may use reference materials, including:

• IET On-Site Guide

• BS 7671

• Internet access

Before attempting questions, candidates must read all task information carefully.

Drawings 5357-A1 to A6 are required. For correct scaling, these drawings must be provided in A3 format. Mark-ups may be completed in A4 if preferred.

All questions must be answered. Responses may be written in the spaces provided or produced electronically on separate titled sheets.

The drawings represent a proposed new hotel extension and pool/café block. Building design information is provided in the specification. Candidates may make reasonable assumptions and must justify them.

Candidate Pre-Assessment Plan

• I am aware of the assessment requirements, criteria, and time allocation.

Assessment Completion Confirmation

The task has been completed to the required standard.

Tutor Feedback

(Space for assessor comments after marking)

Building Specification

Hotel Extension

• Concrete raft foundation with 50 mm screed on ground floor

• First-floor: chipboard on 100 mm timber joists

• Walls: thermolite blocks, uPVC cladding, cavity, inner blockwork and plaster finish

• Partitions: blockwork with plaster finish

• Roof: tiled on timber truss with waterproof membrane

• Ceilings: plasterboard under timber joists

Construction Details

• Reinforced concrete base forming pool and basement floor, tiled throughout

• First floor: precast concrete on steel supports with 50 mm screed, non-slip vinyl

• Basement walls: reinforced concrete with internal uPVC cladding

• Basement ceiling: underside of concrete floor

• Café area: timber frame with uPVC outer cladding, insulation, plasterboard lining

• Café roof: tiled, decorative wooden trusses, plasterboard infills forming open A-frame roof space

• Kitchen area: enclosed plasterboard ceiling at 2.4 m

• Partitions: aluminium-framed plasterboard

Electrical Installation

Supply Arrangement

• Existing hotel uses 400 V three-phase TN-C-S system

• Supply capacity is adequate for the new installation

• New CCU will supply distribution circuits

Measured values:

• Ze = 0.09 Ω

• PFC = 5 kA

For the pool/café block after installation of the new three-phase distribution circuit:

• Zdb = 0.11 Ω

• PFC = 3.7 kA

Fire Alarm

• Specialist installation

• Requires a 13 A un-switched FCU in the pool/café block to supply the repeater panel

HVAC

• Installed by specialists

• No additional considerations required

Design Specification Details

Ambient Temperatures

• Basement pool areas: 40°C

• Café open area: 25°C

• Kitchen/servery: 35°C

Wiring Systems for Lighting & Small Power

• Basement pool areas: PVC surface conduit with 90°C thermosetting single-core non-sheathed cables

• Café open area: PVC surface conduit with 70°C thermoplastic single-core non-sheathed cables

• Kitchen/servery: same as above

Grouping of Circuits

• Basement pool areas: max 2 circuits grouped

• Café open area: max 1 circuit grouped

• Kitchen/servery: max 3 circuits grouped

Thermal Insulation

• None of the wiring systems are affected

Circuit Lengths

• Must be estimated from scaled drawings

• No circuit should exceed ~30 m

Circuit-Specific Requirements

• Dishwasher (16 A, 230 V): 70°C thermoplastic SWA, three-core, clipped direct

• Servery food equipment (16 A, 400 V TP&N): 90°C thermosetting SWA, five-core, clipped direct

• Pool & sauna equipment (32 A, 400 V TP&N): 90°C thermosetting SWA, five-core, clipped direct

• Fridges: two 16 A single-phase circuits, each fridge on labelled sockets, no additional protection

• Summer house: 32 A distribution circuit, three-core 70°C thermoplastic SWA, clipped direct

Design Project Questions

Question 1

Design a fully labelled circuit diagram showing the three-phase 400 V supply from the substation transformer to the EV charging unit.
Show the complete earth fault loop path.
Detailed board/meter layouts not required, but connection points must be indicated.

Question 2

Select suitable luminaires for all pool/café block areas except sauna, considering:

• energy efficiency

• environmental influences

• aesthetics

On the drawings, mark positions of socket-outlets and FCUs for:

• kettle

• TV

• phone/laptop charging

• 700 W air handling unit

• towel rail

• Mark luminaire positions with identification symbols and a key.
• Show circuit arrangements ensuring a fault in one room does not affect another.
• Mark any additional distribution boards required.
• Show lighting circuit arrangements and switching for the pool/café block.
• Assign each circuit a unique identifier.
• Complete drawing legends using recognised symbols.

Question 3

Select a suitable range of circuit protective devices based on:

• prospective short-circuit currents

• additional protection requirements

• special location requirements

Question 4

For every final circuit in the pool/café block, determine:

• design current

• protective device rating and type

• installation method reference

• rating factors

• minimum CSA for current capacity & voltage drop

• actual voltage drop

• maximum permissible disconnection time (BS 7671)

• earth fault loop impedance

• maximum Zs (BS 7671)

Question 5

For one fridge circuit, determine the minimum CPC size using:

• ADS requirements

• Adiabatic equation (Regulation 543.1.3, BS 7671)

Question 6

Determine the maximum demand for the pool/café block:

1. Before diversity

2. After applying diversity

Question 7

Explain, with a diagram, how electrical separation at a shaver point provides protection against electric shock.

Question 8

List:

• Five typical extraneous conductive parts

• Five typical exposed conductive parts
  within the complex.

Question 9

Complete details relating to earthing and bonding:

• Types of conductors

• Where they occur in this installation

• Minimum permissible CSA values

Question 10

Describe isolation and switching types, including:

• isolation for maintenance

• switching for mechanical maintenance

• functional switching

• further BS 7671 requirements

Assignment Feedback Section

Includes:

• Pass/Fail for each question

• Resubmission outcomes

• Assessor comments

• IQA sampling space

Brief summary of assessment requirements

• Core deliverables:

  • Fully labelled single-line/circuit diagrams (including EV charging TT earthing and earth-fault loop path).

  • Luminaires selection and locations; socket/FCU placement; circuit zoning and unique IDs; distribution board layout and legend.

  • Selection of protective devices (based on prospective short-circuit current and special location needs).

  • Detailed circuit calculations for every final circuit (Ib, In, method reference, rating factors, CSA for current and voltage-drop, actual V-drop, Zs and max Zs, disconnection times).

  • CPC sizing (adiabatic equation) for a fridge circuit.

  • Maximum demand calculations (before and after diversity).

  • Explanation/diagram of electrical separation for a shaver point.

  • Lists and specifications for earthing/bonding, extraneous/exposed conductive parts, isolation and switching requirements.

• Standards & safety: All design choices must reference BS 7671 and manufacturers’ data, justify assumptions, and demonstrate safe, code-compliant practice.

• Assessment outcomes: Each question is marked Pass/Fail; resubmission plan and assessor feedback recorded.

How the Academic Mentor guided the student

1. Clarify brief & plan workflow

   • Reviewed the full task, permitted references, and drawings. Broke the project into manageable subtasks mapped to the 10 questions and set milestones to finish detailed calculations, diagram work and selections within the estimated 20-hour timeframe.

2. Site & drawing familiarisation

   • Walked through drawings 5357-A1–A6 with the student, explained scale use (A3), how to estimate circuit lengths, and noted structural/material information (concrete raft, timber joists, precast floors) that affect cable routing and containment.

3. Supply & earthing strategy (Q1)

   • Taught how to interpret the existing 400 V TN-C-S supply and the rationale for a TT arrangement for EV charging. Coached the student on drawing a clear, fully labelled supply diagram from transformer to unit showing live conductors, protective devices, earth electrode, PME/TT interfaces and the total earth-fault loop path.

4. Lighting, power layout and equipment selection (Q2)

   • Guided luminaire selection using manufacturers’ catalogues focusing on energy efficiency, IP/IK ratings for ambient conditions (40 °C in pool basements), and aesthetics. Helped place socket-outlets, FCUs and special supply points (air handling unit, towel rail, fridges) on the drawings, assign unique circuit IDs and locate additional distribution boards to isolate rooms.

5. Protective device selection (Q3)

   • Demonstrated step-by-step selection of MCBS/RCDs/MCCBs using prospective short-circuit data (PFC, Zdb) and additional protection requirements (e.g., RCD sensitivity in wet areas). Student practised using manufacturer spec sheets to justify device ratings.

6. Circuit design calculations (Q4 & Q5)

   • Provided worked examples for: calculating design current (Ib), choosing In, applying installation method references and grouping/ambient factors, selecting conductor CSA for Iz and voltage-drop limits, computing actual V-drop and verifying Zs and disconnection time against BS 7671. For the fridge CPC, guided the adiabatic calculation and ADS checks for earth-fault protection.

7. Maximum demand and diversity (Q6)

   • Explained methods for summing circuit demands, applying agreed diversity factors and deriving load after diversity. Student completed demand tables and cross-checked result plausibility.

8. Shock protection and separation (Q7)

   • Coached creation of a clear diagram and explanation showing electrical separation for a shaver point (functional insulation, isolated supply, or SELV/mains separation) and how this meets protective measures in BS 7671.

9. Earthing, bonding, isolation and conductive parts (Q8–Q10)

   • Identified typical extraneous/exposed conductive parts for the complex, matched bonding requirements and minimum CSA values per BS 7671, and explained isolation/functional switching types and maintenance isolation protocols.

10. Integration, documentation & QA

    • Helped the student assemble final drawings with legends and symbol keys, compile manufacturer data sheets, annotate assumptions and justifications, perform a final consistency check (IDs, cable routes, voltage-drop, protection coordination), and prepare a clean submission bundle.

11. Rehearsal & assessor readiness

    • Reviewed expected assessor queries, ensured traceability of all calculations to standards and datasheets, and prepared a short cover note explaining any reasonable assumptions.

Outcome achieved and learning objectives covered

Outcome:

• Student produced a complete, standards-referenced design submission: scaled and annotated drawings (circuit layouts, luminaire and socket positions, distribution board locations), single-line diagrams including EV TT earthing path, manufacturer selections for luminaires and protective devices, full circuit calculation set (Ib, In, Iz, CSA, voltage-drop, Zs checks), CPC adiabatic calculation for a fridge circuit, maximum demand with diversity, and written explanations/diagrams for shock protection, earthing/bonding and isolation strategy. Submission was coherent, justified, and ready for assessor marking; the student also completed the 2365-625 e-volve test.

Key learning objectives demonstrated:

• Application of standards: Correct use of BS 7671 principles for design, protective device selection, disconnection times and earthing/bonding requirements.

• Technical design skills: Generation of compliant single-line and circuit diagrams, circuit zoning that isolates faults to single rooms, and logical distribution board placement.

• Electrical calculations: Accurate determination of design currents, cable sizing for current and voltage-drop, earth-fault loop impedance checks, CPC sizing via adiabatic equation, and maximum demand/demand-after-diversity computation.

• Product selection & justification: Use of manufacturers’ data to select luminaires and protective devices based on environment, thermal constraints and short-circuit ratings.

• Risk awareness & safety: Consideration of ambient temperatures, special locations (wet areas), RCD/application of additional protection, and safe isolation procedures for maintenance.

• Professional documentation & reasoning: Clear labelling, legends, documented assumptions, referenced standards and datasheets all demonstrating professional design practice suitable for client handover and assessment.

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