City & Guilds 2391-51 flashcards

32 cards. Read the term and the definition here. The deck at the top of this page is optional.

BS 7671 legal status

BS 7671 is the national wiring standard; it is non-statutory, but compliance is commonly accepted as evidence that statutory duties under the Electricity at Work Regulations have been met.

EAWR Regulation 14

Prohibits work on or near live conductors unless it is unreasonable for the equipment to be dead and suitable precautions, including a written risk assessment, have been taken.

Part P Building Regulations

Applies to electrical installations in dwellings in England and Wales; certain work is notifiable to building control and the work must comply with Part P requirements.

GS38 test lead requirements

Test probes to GS38 have no more than 4 mm exposed metal tip, finger guards, fused leads and adequate voltage category rating, protecting the user during live testing.

Prove dead procedure

Identify and isolate the circuit, lock off, prove the voltage detector on a known source, test the conductors, then re-prove the detector to confirm it still works.

Lock off and warning notice

The isolation device is padlocked with the key retained by the person working, and a warning notice is fixed so others cannot inadvertently restore the supply.

Two-pole voltage detector

An approved two-pole device to GS38 is used to prove conductors dead; non-contact or single-pole voltage indicators are not acceptable for proving dead.

Competence under EAWR

Regulation 16 requires that no person works on electrical systems unless competent to do so, or is supervised by someone who is competent, preventing unsafe working.

Sampling in periodic inspection

Periodic inspection may examine a sample of the installation where justified; the sample is increased if defects are found and the approach is recorded as a limitation.

Recording limitations

Items not inspected or tested, such as inaccessible areas or circuits omitted from the sample, must be listed on the condition report so the reader knows the extent covered.

Previous documentation review

Prior certificates, schedules of test results, drawings and records of alterations are reviewed before a periodic inspection to plan sampling and identify changes.

Agreeing extent with client

Before starting, the client and inspector agree in writing which parts of the installation and which circuits are covered, and what limitations apply.

Main protective bonding size

The main protective bonding conductor size is determined from the supply neutral conductor size using BS 7671 Table 54.8, typically 10 mm2 for a 25 mm2 neutral.

Safe zones for buried cables

Cables buried in walls must run within defined safe zones, typically within 150 mm of a corner or ceiling or aligned with an accessory, otherwise extra protection is required.

Signs of heat damage

Discoloured or brittle insulation, melted plastic, blackened terminals and a burning smell indicate overheating from loose connections or overload and require investigation.

Consumer unit enclosure checks

The enclosure should be sound, correctly IP rated for its location, with no unused open knockouts, intact barriers and a legible and accurate circuit chart.

EIC versus EICR

An Electrical Installation Certificate is issued after initial verification of new work; an Electrical Installation Condition Report records the condition of an existing installation after periodic inspection.

Initial verification coverage

Initial verification covers the whole new installation or alteration, comparing it with the design, and requires full inspection and testing without any sampling.

Purpose of periodic inspection

Periodic inspection determines whether an existing installation is safe for continued use, identifying deterioration, damage, defects and non-compliance with the current standard.

Domestic EICR interval

Guidance suggests a maximum of ten years between periodic inspections for a domestic installation, or at a change of occupancy or change of use.

Ring final continuity readings

End-to-end resistances r1, rn and r2 are measured; r1 should equal rn, and r2 is approximately 1.67 times r1 for 2.5 mm2 line and 1.5 mm2 CPC.

Ring final R1+R2 value

After cross-connecting line and neutral at the board, the expected R1+R2 at each socket is (r1+r2)/4, with readings increasing towards the mid-point of the ring.

Insulation resistance minimum

For circuits up to 500 V the test is at 500 V DC and the minimum acceptable insulation resistance is 1 Mohm; SELV and PELV require 250 V DC and 0.5 Mohm.

Main bonding continuity value

Continuity of main protective bonding is measured between the main earthing terminal and the bonding clamp, with a typical acceptable result of 0.05 ohm or less.

External earth loop impedance

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

Zs 0.8 rule

Measured Zs should not exceed 0.8 times the tabulated maximum Zs, because tabulated values apply at 20 degrees C while conductors run hotter in service.

RCD five-times tripping time

A general non-delay RCD should trip within 40 ms when tested at five times its rated residual operating current, and the test is repeated on both half-cycles.

Prospective fault current measurement

Prospective short-circuit current between line and neutral and prospective earth fault current between line and earth are both measured at the origin, and the higher is recorded.

C1 classification code

C1 means danger is present, there is a risk of injury, and immediate remedial action is required, usually involving isolation of the affected circuit or installation.

C2 classification code

C2 means a potentially dangerous condition exists and urgent remedial action is required; a report containing any C2 observation cannot be recorded as satisfactory.

C3 classification code

C3 means improvement is recommended; the condition is not dangerous but would benefit from improvement, and no immediate action is required.

FI classification code

FI means further investigation is required because a defect or departure is suspected but cannot be confirmed without additional access, testing or dismantling.