Periodic inspection of existing domestic and similar installations

 

  • Q1. Where can I find general guidance on the use of Classification Codes for domestic electrical installation condition reports?

    General guidance on the use of Classification Codes is available in Issue 3 of the Electrical Safety Council’s Best Practice Guide No 4, which may be viewed or downloaded free of charge by clicking here

  • Q2. During periodic inspections of domestic electrical installations, I often find that cables that are concealed in walls at a depth of less than 50 mm have no additional protection by means of an RCD, as is now required for installations complying with the 17th Edition. What Classification Code should I give?

    Although existing installations need to be assessed against the requirements of the 17th Edition, this does not necessarily mean that they require upgrading, unless a departure from the latest requirements constitutes an immediate or potential danger. However, it would usually be appropriate to recommend improvement by giving the observation a Classification Code C3.

    Regulation number(s)

    • Introduction to BS 7671: 2008 incorporating Amendment 1

  • Q3. Where can I find the limiting values of measured earth fault loop impedance for BS 3871 circuit breakers?

    Click here!

  • Q4. What Classification Code should be given if it is found that there is no supplementary bonding in a bathroom having extraneous- or exposed-conductive-parts, and the conditions given in Regulation 701.415.2 for its omission are not met?

    Classification Code C2. Where the presence of supplementary bonding cannot be confirmed by inspection, it may be verified by a continuity test (< 0.05 Ω)

  • Q5. Is it necessary to verify voltage drop during a periodic inspection?

    Verification of voltage drop is not normally required unless there is considered to be a voltage drop problem.

    Regulation number(s)

    • 621.2

  • Q6. What should be recommended if, during a periodic inspection, the safety of an installation forming part of a TT system is found to be relying on a voltage-operated earth-leakage circuit-breaker (VOELCB) for fault protection?

    If a VOELCB on a TT system fails to operate when tested with an instrument or integral test button, this would warrant a Classification Code C2 (potentially dangerous).

    But, subject to the VOELCB being proved to operate correctly, continued reliance on it for fault protection (protection against indirect contact) would normally warrant a Classification Code C3 (improvement recommended).

    However, if the VOELCB relies on a water pipe not permitted by Regulation 542.2.4 to be a means of earthing, this should attract a Classification Code C2 (potentially dangerous). 

  • Q7. What should I recommend in electrical installation condition report if I find that an existing installation still relies for fault protection on a voltage-operated earth-leakage circuit-breaker?

    If the device fails to trip when the integral test button is operated, the device should be replaced with RCD protection as a matter of urgency (Classification Code C2).

    If the device trips on operation of the test button, it may remain in service but improvement should be recommended (Classification Code C3).

    However, the user should be given clear instructions to test the device at quarterly intervals by means of the integral test button.

    The user should also be advised that the voltage-operated device should be replaced with RCD protection at the earliest opportunity to enhance the safety of the installation.

  • Q8. In an existing domestic installation, are 16 mm2 single-core pvc/pvc meter tails (having a current-carrying capacity of 87 A clipped direct) adequate if the rating of the distributor’s cut-out fuse is 100 A?

    This size of tails may be adequate provided the maximum demand of the installation, taking into account the load characteristics (diversity and load profile), does not exceed the current-carrying capacity of the tails, and also provided that the requirements of Regulation 434.5.2 for protection of the tails against fault current are met.

    As a practical tip, the current-carrying capacity of the meter tails is likely to be adequate if they have been in service for several years and there are no signs of thermal damage at the terminations or to the cable sheath or insulation.

    Regulation number(s)

    • 311.1
    • 433.3.1(ii)
    • 434.5.2

  • Q9. In an existing domestic installation, is a 10 mm2 or 6 mm2 earthing conductor adequate if the rating of the distributor’s cut-out fuse is 100 A?

    This size of earthing conductor will be adequate if the requirements of Regulation 543.1.3 (adiabatic equation) are met.

    However, if the supply is PME, the earthing conductor is usually required to be at least 10 mm2

    Regulation number(s)

    • 543.1.3
    • 542.3.1
    • 544.1.1

  • Q10. What is the recommended sequence for testing RCDs?

    Preferably, RCDs should be tested in the sequence of: x1 IΔn, x5 IΔn (if required for additional protection), followed by x0.5 IΔn and then finally the test button trip.

    However, some automated test instruments test in the sequence of: x0.5 IΔn followed by the x1 IΔn test and then the x5 IΔn test (if required for additional protection).

    In any case, the test button should be operated last in the test sequence.

  • Q11. What is the procedure for periodic inspection and testing when an electrical installation is not energised to enable the necessary live testing to be undertaken?

    Live testing is an essential part of establishing whether an installation is in a satisfactory condition for continued service, which is the purpose of a periodic inspection.

    It will be necessary for the live testing to be completed, and therefore for the supply to be available, before an Electrical Installation Condition Report can be issued.

  • Q12. Are the relevant tests of Regulations 612.2 to 612.13, for example continuity of protective conductors and earth fault loop impedance, applicable to parts of systems such as room and cylinder thermostats, motorized valves and programmers?

    Yes. Automatic Disconnection of Supply (ADS) is a commonly-used protective measure against electric shock in such systems. The continuity of protective conductors to each point should be confirmed. The value of R2 or (R1 + R2) may be used to estimate the maximum earth fault loop impedance of each control circuit for verification purposes. Insulation resistance tests should also be carried out, precautions having been taken to avoid damage to any electronic components. The results should be recorded on a schedule of test results.

    Regulation number(s)

    • 411.3.1.1
    • 411.3.2
    • 612.9

  • Q13. Is it acceptable to calculate (R1+R2) values when carrying out periodic inspections, using measured loop impedance values?

    No. In any event, it is not essential to measure (R1 + R2) values for a Condition Report.

  • Q14. Is it acceptable to carry out dead tests on individual circuits within an energised distribution board when carrying out a periodic inspection?

    No, as it involves avoidable live working (unless the construction of the distribution board provides a suitable form of separation. See the BEAMA Guide to Forms of Separation).

  • Q15. When carrying out a periodic inspection, is it acceptable to use a wander lead to carry out protective conductor continuity testing to exposed-conductive-parts (such as metallic accessory plates) with the installation still energized?

    Yes, provided that the continuity test instrument, test leads and probes are in good condition (to avoid the risk of electric shock). This test method should not be used inside enclosures containing live parts that are energized (to avoid the risk of touching a live part with the wander lead probe).

  • Q16. How should the extent of inspection and testing (sampling rate) be determined for a periodic inspection?

    The level of sampling to be applied must be agreed in advance with the person ordering the work. Guidance on sampling can be found in IET Guidance Note 3.

  • Q17. When undertaking a periodic inspection on a domestic electrical installation having more than one consumer unit, do I need to complete a separate Condition Report for each part of the installation?

    Not necessarily. It depends on whether all the required information for each part of the installation can be recorded on one Condition Report.

  • Q18: When undertaking a periodic inspection on a domestic installation, it is found that, since the wiring was installed, it has been covered by thermal insulation. What, if anything, should be recorded in the Condition Report?

    In many cases, the covering of cables in thermal insulation, whilst not recommended, does not result in overheating sufficient to damage or degrade the cable insulation or connected accessories, so would not need to be recorded in the Condition Report.

    However, if the inspector has reasonable doubt about the adequacy of the cable rating in relation to the nature of the load (for example there are signs of overheating), such that there is potential danger, a Classification Code C2 (potentially dangerous) would be appropriate.

    Regulation number(s)

    • 523.9

  • Q19. On the new Electrical Installation Condition Report, the first few lines of the inspection (1.1 – 1.6 & 3.1) is the verification of the distributor’s/supply intake equipment. What should I recommend if that equipment is in a dangerous or potentially dangerous condition?

    Where inadequacies in distributor’s equipment are observed, the contractor should recommend that the person ordering the report requests the distributor or meter operator, as appropriate, to carry out remedial work as necessary to remove the danger or potential danger.

    Distributors and meter operators have an obligation under the ESQCR to maintain their equipment, so far as is reasonably practicable, to prevent danger.