12.1 The Practical Assignment & Establishing a Safe System of Work
Key Takeaways
- Learning outcome 5 carries none of the 60 multiple-choice questions but is the whole of the 2391-502 practical assignment, which must be passed to achieve the award
- AC5.1 requires you to establish a safe system of work appropriate to the installation: risk assessment, permission to work, the right instruments, and control of others on site
- AC5.2 requires safe isolation in accordance with HSE guidance - identify, obtain permission, prove the indicator, isolate, secure with a unique lock and caution notice, prove dead, re-prove the indicator
- Proving dead means testing between every combination of conductors, not just line to neutral: on three-phase that is ten separate checks
- Assessors fail candidates for procedural errors far more often than for wrong readings - an unproved voltage indicator or an unsecured isolation ends the assessment
Where the Practical Sits in the Qualification
The test specification gives learning outcome 5 zero questions out of the 60 in the multiple-choice paper. It would be a serious mistake to read that as "LO5 does not matter". LO5 is "Perform inspection and testing of electrical installations" — it is assessed by the 2391-502 practical assignment, and the City & Guilds handbook is clear that candidates must successfully complete one practical assignment and one online multiple choice test. Both.
The assignment is carried out at an approved centre on a real or purpose-built installation. In outline it requires you to:
- establish a safe system of work and carry out a safe isolation (AC5.1, AC5.2);
- carry out an inspection in accordance with BS 7671 and IET Guidance Note 3, and complete a schedule of inspections (AC5.3, AC5.4);
- carry out the tests in accordance with BS 7671 and GN3 (AC5.5);
- verify the results for compliance or classification (AC5.6);
- complete the documentation — an Electrical Installation Certificate, an Electrical Installation Condition Report, schedules of inspections, schedules of test results, and a Minor Electrical Installation Works Certificate as required (AC5.7).
There is also a short-answer written paper within the assignment pack — commonly four questions, open book. It is part of the 2391-502 assignment, not a separate third assessment. Your centre will confirm the timings, which City & Guilds does not publish in the qualification handbook.
The single most useful preparation: rehearse the whole sequence on a rig, against the clock, including filling in the paperwork. Candidates rarely fail on technical knowledge. They fail on procedure, on time, and on incomplete documentation.
AC5.1 — Establishing a Safe System of Work
A safe system of work is everything you put in place before you touch the installation. The assessor is watching for it from the moment you walk in.
1. Assess the risk
Identify the hazards this specific installation presents: shock and burn from live parts, arc flash at the origin where prospective fault current is highest, stored energy in capacitors, working at height, confined access, and the consequences of switching something off. Under the Management of Health and Safety at Work Regulations 1999 this assessment is a legal requirement, not a formality.
2. Obtain permission
Confirm who owns the installation, who may authorise the supply to be interrupted, and what must stay energised. On a live site this may mean a permit to work. Never isolate a supply you have not been authorised to isolate — the consequences of stopping the wrong system can be far worse than the electrical risk you were managing.
3. Establish the extent and limitations
Agree what you will inspect and test, and what you will not. This is both a safety control and a reporting requirement (see section 3.4).
4. Select and check the equipment
- Instruments appropriate to each test, within calibration, with the serial numbers noted for the schedule.
- Leads and probes complying with HSE GS38 — fused, shrouded, finger-guarded, minimal exposed tip.
- An approved two-pole voltage indicator and a proving unit. Not a multimeter.
- A lock-off kit with a unique key and caution notices.
- Appropriate PPE for the work and the location.
5. Control the area and the people in it
Barriers or signs where live parts will be exposed, and communication with anyone who might restore a supply or use the equipment. Then, when you have finished, restore everything you altered and confirm the installation is left in its intended operating state.
AC5.2 — Safe Isolation, Step by Step
This is the procedure the assessor is most likely to stop you on, and it is the procedure that most often appears in the written paper. It follows HSE guidance (HSG85, Electricity at Work: Safe Working Practices, with GS38 for the instruments) and gives effect to EAWR Regulation 13.
| Step | Action | Why it matters |
|---|---|---|
| 1 | Identify the circuit or equipment to be isolated, using the circuit chart, labelling and your own tracing | Isolating the wrong circuit leaves you working live and may shut down something critical |
| 2 | Obtain permission to isolate from the duty holder or responsible person | Legal and practical authority to interrupt the supply |
| 3 | Select an approved voltage indicator to GS38 and prove it on a known live source or a proving unit | An indicator that is already faulty will show dead on a live conductor |
| 4 | Isolate at the correct point — main switch, circuit-breaker, or by withdrawing the fuse | The point of isolation must be secure and must actually break the supply to the point of work |
| 5 | Secure the isolation: lock off with a device having a unique key held by you, and fit a caution notice | Prevents anybody else restoring the supply while you are working |
| 6 | Prove dead at the point of work, testing every combination of conductors | The isolation may not be complete — back-feeds, borrowed neutrals and second supplies are real |
| 7 | Re-prove the voltage indicator on the known source or proving unit | Confirms the indicator did not fail between steps 3 and 6, which would have made step 6 meaningless |
| 8 | Begin work | Only now |
Steps 3 and 7 together are the prove–test–prove sequence. Omitting either is an automatic fail, because without both the dead reading proves nothing.
Proving dead: the combinations
Candidates lose marks here by testing line to neutral and stopping.
Single-phase — 3 checks:
- Line to Neutral
- Line to Earth
- Neutral to Earth
Three-phase — 10 checks:
- L1–L2, L1–L3, L2–L3 (three line-to-line)
- L1–N, L2–N, L3–N (three line-to-neutral)
- L1–E, L2–E, L3–E (three line-to-earth)
- N–E (neutral to earth)
The neutral-to-earth check is the one most often skipped and one of the more important: a voltage between neutral and earth indicates a borrowed neutral, a broken neutral, or a supply that is still connected somewhere you have not found.
Why safe isolation is done at all
It protects the inspector from shock, burn and arc flash; it protects other people on site from equipment starting unexpectedly; and it protects the installation and its loads from damage caused by testing an energised circuit. EAWR Regulation 14 permits live working only where it is unreasonable to work dead, it is reasonable to work live in all the circumstances, and suitable precautions are taken. The live tests in this qualification — loop impedance, prospective fault current, RCD operation — are the recognised exceptions, because they cannot be performed any other way.
A candidate proves their voltage indicator on a proving unit, isolates and locks off the circuit, proves dead at the point of work, and begins the dead tests. What essential step has been omitted?
How many separate conductor combinations must be checked when proving dead on a three-phase and neutral supply?