City & Guilds 2391-51 cheat sheet

BS 7671 (IET Wiring Regulations) is non-statutory, but enforcement bodies and courts accept compliance as evidence of reasonable practicability under the Electricity at Work Regulations 1989.

Electricity at Work Regulations 1989: Reg 4 (systems and protective equipment), Reg 12 (isolation), Reg 13 (work on dead equipment), Reg 14 (live working), Reg 16 (competence).

Health and Safety at Work etc. Act 1974 places duties on employers and self-employed persons to ensure safety so far as is reasonably practicable, including contractors on site.

Part P of the Building Regulations 2010 applies to fixed electrical installations in dwellings in England and Wales; notifiable work requires building control notification.

IET Guidance Note 3 gives the recognised practical guidance on inspection and testing to BS 7671 Part 6 (Chapters 61 to 64).

HSE GS38 specifies test probe and lead requirements: maximum 4 mm exposed tip, finger guards, fused leads and adequate voltage category rating.

The Electricity Safety, Quality and Continuity Regulations 2002 govern the supply and distribution network, not the consumer's installation.

The Electrical Safety Standards in the Private Rented Sector (England) Regulations 2020 require a five-yearly EICR by a competent person, with remedial action within 28 days.

Non-statutory documents (BS 7671, guidance notes, codes of practice) create no legal duty by themselves; duties arise from statute and statutory instruments.

Safe isolation sequence: identify the circuit and all sources, isolate, lock off and retain the key, post a warning notice, prove dead with an approved two-pole detector, then re-prove the detector.

The voltage detector must be proved on a known live source or proving unit before and after testing the isolated conductors.

Non-contact voltage sticks and single-pole testers are not acceptable for proving dead; only an approved two-pole device to GS38 is used.

Parallel supplies must be isolated: standby generators, UPS, PV inverters, dual supplies, control circuits and signal circuits.

EAWR Reg 13: equipment made dead must be isolated, secured against reconnection where practicable, and proven dead at the point of work.

Live working is permitted only where it is unreasonable to work dead and suitable precautions, including a written risk assessment, are taken under EAWR Reg 14.

EAWR Reg 16 makes competence a legal requirement; work must be supervised where the person is not competent to carry it out unaided.

Test leads to GS38 are fused, fitted with finger guards, have 4 mm maximum exposed tips, and are inspected for damage before every use.

Collect previous EICRs, EICs, schedules of test results, drawings and records of alterations before attending site.

Agree the extent, limitations and sampling approach with the client in writing before the inspection starts.

Sampling may be used on existing installations, but the sample must be increased where defects or non-compliance are found.

Record every limitation on the report: inaccessible areas, circuits not sampled, equipment not energised, buried cables not inspected.

Confirm the earthing system (TN-S, TN-C-S, TT), nominal voltage, supply capacity and any special locations before testing.

Check that test instruments have a valid calibration certificate and correct category rating, and prove leads and battery condition.

Plan shutdowns, permits to work, access arrangements and safe isolation with the duty holder before energised testing.

Identify special installations and locations (bathrooms, swimming pools, agriculture, fire alarm and emergency lighting systems) requiring specific inspection.

Check the origin: intake condition, meter, main switch or isolator, distributor's earthing facility and presence of a main protective bonding conductor.

Verify main protective bonding to metallic services (water, gas, oil, structural steel) is present, correctly sized to Table 54.8 and securely clamped.

Check distribution boards: enclosure condition, IP rating, unused open knockouts, barriers and shrouds, labelling and circuit chart accuracy.

Look for heat damage: discoloured insulation, blackened or melted terminations, burnt smells and arcing marks at connections.

Check cables for sheath damage, correct support, mechanical protection, routing within safe zones and fire barrier penetration.

Check accessories for cracks, missing screws, correct IP rating, bathroom zoning compliance, damaged sockets and signs of overheating.

Check protective device rating against cable capacity (Ib <= In <= Iz) and correct device type for the earthing arrangement and disconnection time.

Confirm RCD protection where required and notices such as the RCD test notice, SPD notice and danger or dual supply labels.

Record deterioration such as corrosion, water ingress, rodent damage, loose connections and unauthorised DIY alterations as coded observations.

Initial verification applies to new installations and to alterations or additions, and is carried out before the installation is put into service.

Periodic inspection applies to existing installations already in service and determines fitness for continued use.

Initial verification requires full inspection and testing of the work with no sampling; periodic inspection may use sampling with recorded limitations.

Initial verification produces an Electrical Installation Certificate (EIC); periodic inspection produces an Electrical Installation Condition Report (EICR).

The EICR is a report on condition, not a certificate of compliance with the current edition of BS 7671.

Periodic inspection considers age, use, wear, environment, previous records and any change of use or occupancy.

Guidance intervals: domestic about 10 years, rented domestic 5 years, commercial 5 years, industrial 3 years, and at change of occupancy.

The scope agreement defines circuits included and excluded, the sampling level, limitations, and whether remedial work is to be quoted.

Both activities follow the same test sequence, but periodic testing is proportionate to the agreed sample and the available records.

Continuity of circuit protective conductors is measured with a low-resistance ohmmeter with leads nulled, giving R1+R2 for each circuit.

Main protective bonding continuity is measured between the main earthing terminal and the bonding clamp; a value of 0.05 ohm or less is typical evidence of a sound connection.

Ring final circuit: measure r1, rn and r2 end to end; r1 should equal rn and r2/r1 is about 1.67 for 2.5 mm2 line with 1.5 mm2 CPC.

Ring cross-connection: expected R1+R2 at a socket is (r1+r2)/4, while (r1+rn)/4 gives the expected loop reading at each socket.

A ring with a broken conductor or an unintended spur shows socket readings that do not follow the expected progression from the board.

Insulation resistance: 500 V DC with a minimum of 1 Mohm for circuits up to 500 V; 250 V DC and 0.5 Mohm for SELV and PELV.

Test insulation between live conductors and earth, i.e. line and neutral connected together to the protective conductor, to protect connected electronic equipment.

Isolate and disconnect loads, SPDs, dimmers, electronic ballasts and controls before the insulation test, and discharge after testing.

Polarity by dead testing confirms line is connected to the centre pin or line terminal and that all single-pole devices are in the line conductor.

Ze is measured at the origin with the installation isolated, main switch off and main earthing conductor disconnected, using an earth fault loop impedance tester.

Zs is measured at the furthest point of each circuit, or calculated from Ze + R1+R2, and compared with the maximum tabulated value.

Measured Zs should not exceed 0.8 times the tabulated maximum Zs from BS 7671 to allow for conductor operating temperature.

Prospective fault current: measure PSCC (line to neutral) and PEFC (line to earth) at the origin and record the higher of the two.

The recorded prospective fault current must not exceed the short-circuit rating (Icn) of the protective devices installed.

RCD test sequence: half rated current must not trip; rated current within 300 ms; five times rated current within 40 ms for general non-delay RCDs.

Test RCDs on both half-cycles of the waveform and at each outlet protected by the device, particularly 30 mA additional protection.

Functional testing confirms correct operation of isolators, switches, RCD test buttons, timers, indicators and interlocked equipment.

Energised testing requires a risk assessment, insulated tools and PPE, protection from adjacent live parts, and adequate working space and lighting.

The EICR records installation details, extent and limitations, summary of condition, coded observations, schedules of inspection and test results, and the next inspection date.

C1 = danger present, risk of injury, immediate action required, usually isolation of the affected part of the installation.

C2 = potentially dangerous condition, urgent remedial action required.

C3 = improvement recommended; not dangerous but the installation would benefit from improvement.

FI = further investigation required without delay because a suspected defect cannot be confirmed with the access or information available.

No code is recorded for items that comply, are not applicable, or where a limitation was agreed with the client.

The overall assessment is recorded as satisfactory only where no C1 or C2 observations are present.

The next inspection interval is recommended from the installation type, use, environment, condition and duty holder requirements.

Test results are recorded on the schedule of test results with circuit references, and the signed report is issued to the person ordering the work.