Ask the experts

During our recent online Branch Updates, Members submitted a range of questions for our Technical Advisers to tackle. Here is a small selection of the queries we received, along with the answers from our experts…


01 I’ve been asked by several clients and potential clients to carry out remedial works in respect to an Electrical Installation Condition Report (EICR) carried out by another electrician. This always throws up questions and queries on the code attributed.


Firstly, we need to understand that during the inspection process the ‘Inspector’ should use their skills, knowledge and experience as the competent person to decide on the classification code to be used. At the end of the report THEY will be the one signing the report to accept full responsibility for the content and most importantly the accuracy of the report. Yet we still see the classification coding being harshly applied in some instances.

As Technical Advisers, we will always recommend that all inspectors refer to the Guide to EICRs issued by Electrical Safety First. The example of observations found and potential codes has been discussed and agreed by several organisations, including SELECT, so we have an industry-wide template.


As soon as we are back out on the road, we will be carrying handy-sized copies of this, but in the meantime download a copy at bit.ly/ESF_Best_Practice

02 To SPD or not SPD, that is the question: Should installations always be provided with surge protection devices (SPDs)?


Members regularly ask if installations should be provided with SPDs. To answer the question, let’s start with Regulation 443.4, which is on page 101 of BS 7671:2018, and says that protection against transient overvoltages shall be provided where the consequence caused by overvoltage could:

  • Result in serious injury or loss of life to humans, or

  • Result in interruption of public services and/or damage to cultural heritage, or

  • Result in interruption of commercial or industrial activity, or

  • Affect a large number of co-located individuals.

For all other cases a risk assessment according to Regulation 443.5 shall be performed in order to determine if the protection against transient overvoltages is required. This can also be found on page 101 of BS 7671:2018. Here are a few notes about the risk assessment:

  • CRL=fenv/(LpxNg) – there is nowhere on current certification to record this calculation to show you have completed the risk assessment

  • Fenv – an environmental factor selected according to table 443.1, page 103 of BS 7671:2018

  • Lp – the risk assessment length in Km calculated using Lp=2 Lpal + Lpcl + 0.4 LPAH+0.2 LPCH(KM) on page 103 of BS 7671:2018

  • Ng – the lighting ground flash density (flashes per km2 per year) relevant to the power line and connected structure. See figure 44.2, page 102 of BS 7671:2018.

If the risk assessment is not performed, the electrical installation shall be provided with protection against transient overvoltages, except for single dwelling units where the total value of the installation and equipment does not justify such protection. If you’ve been on SELECT’s 218 training course, then these risk assessments will have been covered. Indeed, some Members may remember our own in-house example, where Technical Adviser Darren Sweeney carried out the calculation. Given that he has overhead lines in his back garden which are 20m from the house, you can probably guess the outcome too!

Within this regulation there is also an exception for single dwelling units, which mentions the total value of the installation and the equipment therein not justifying the protection. On this, we always advise caution to those attending if the job to be done is significant, and it may well be an ideal time to install the SPD, e.g. consumer unit upgrade or rewire. Discussion with the client and advising of what an SPD is, does and protects would certainly be advisable.


As the competent and knowledgeable electrician, having some knowledge in this will help. If you attended the SELECT Toolbox Talk in 2017 then you will have had the pleasure of our SPD presentation and may have gained some valuable understanding. If not, then I recommend the BEAMA Guide which can be accessed at bit.ly/BEAMA_SPDs


NOTE: There are proposals to change the wording to these regulations in the draft for public comment (DPC) of Amendment 2:2022 to BS 7671:2018 which includes plans for a discussion between the designer and the installation owner to determine if SPD protection is required or not in dwellings. The outcome following review of DPC comments by JPEL/64 will no doubt be of interest to SELECT Members.

03 To overcome thermal insulation issues, is it permissible to protect a ring final circuit using 2.5mm² cable and a 20A protective device?


Firstly, let’s look at reference methods and follow on to Appendix 4 Table 4D5 (page 409) of BS 7671: 2018. Thermoplastic insulated and sheathed flat cable with protective conductor totally surrounded ref method 101 current carrying capacity is 17A. Then let’s look at Regulation 523.9 (page 143) which also references to Appendix 4 that we have just considered.


A cable should preferably be installed in a location where it is unlikely to be covered in thermal insulation. Where a cable is to be run in a space to which thermal insulation is likely to be applied, it shall, where practicable, be fixed in a position such that it will not be adversely affected by the amount of thermal insulation.

To meet the requirements of Regulation 523.9 requires “where a single cable likely to be totally surrounded by thermally insulating material over a length of 0.5m or more, the current-carrying capacity shall be taken, in the absence of more precise information, as 0.5 times the current carrying capacity for that cable clipped direct to a surface and open (Reference Method C)”, also discusses the derating factor form table 52.2 regarding the cable surrounded by thermal insulation. Where applicable, the nature of the load (e.g. cyclitic) and reference to chapter 31, Maximum demand and diversity, may be taken into account.


For economic and reliable design of an installation within thermal limits and admissible voltage thereof, diversity may be taken into account reference to On-Site Guidance Appendix A and in particular Appendix H standard circuit arrangements for household and similar installations.


The installed current carrying capacity (Iz) calculated must not be less than 20A for a ring circuit using 2.5mm2. Regulation 433.1.204 also states that the load current in any part of the circuit is unlikely to exceed for long periods the current carrying capacity (Iz) of the cable.


A sensible approach when it comes to ring final circuits reference can also be made to Appendix 15 (page 505) which has useful information and guidance.


For background information, ring final circuits were developed in Britain in 1927, in the 9th Edition of the wiring regulations. Use was intended for light loads only, e.g. vacuuming etc. Regulation 433.2.1 (page 89), Position of devices for protection against overload footnote, states: “A reduction in current-carrying capacity may be due to a change in cross-sectional area, method of installation, type of cable or conductor, or in environmental conditions.”


So, in answer to the initial question, it WOULD be acceptable to protect a ring final circuit using 2.5mm2 cable protected by a 20A overcurrent protective device. However, the designer of the installation must take into account the load connected to the socket outlets, the method of cable installation and switch-on surges when using reduced current overcurrent protective devices.


A similar answer to the above is given below, and is what electrical industry bodies including SELECT agreed under the auspices of Electrical Safety First’s Wiring Regulations Advisory Group (WRAG):


Q1.9: To overcome thermal insulation issues, is it permissible to protect a ring final circuit using 2.5 mm² cable using a 20A protective device? Yes, if the effective current carrying capacity of the cable is at least 12.5A (20A × 20/32), so as to effectively have the same ‘deemed to comply status’ as Regulation 433.1.204 gives to 30A and 32A ring final circuits. Regulation number(s): 433.1.204. See more at bit.ly/QAthermal.

04 I’ve seen that the 5th Edition of the IET’s Code of Practice for in-service inspection and testing of electrical equipment is now available after being released in 2020. What changes have occurred in this new publication?

This was previously covered in detail in the December 2020/January 2021 issue of CABLEtalk. In a nutshell, the main changes are:

  • The terms ‘portable’ and ‘moveable’ have been removed

  • Table 7.1 has been removed, with more emphasis placed on risk assessments for determining the frequency of inspection and testing of electrical equipment

  • New terminology is used in product safety standards with new classifications of ES1, ES2 and ES3 introduced to replace SELV, ELV and LV.


Members requiring any further information should contact the Technical team.

05 During electric vehicle (EV) charger installs, we’re required to fill out an Electrical Installation Certificate via SELECTcerts as per BS 7671. However, we currently have to list and append all inspections separately, using a printed and scanned-in version of the model form Annex B on page 113 of the latest Code of Practice (Electric Vehicle Charging Equipment Installation – 4th Edition). Is there any way of incorporating this into SELECTcerts?

Electric vehicle charging is classed as a ‘Special Location’ and thus on the inspection schedule supplied with the BS 7671:2018 Electrical Installation Certificate, section 11 will require to be ticked as this installation work falls under Section 722. A model checklist for this scope of works is given in the Code of Practice for Electric Vehicle Charging Equipment Installation, 4th Edition, which is available from SELECT. In Annex B, C and D, model checklists are given for domestic, commercial and on-street installations. SELECT will look into the feasibility and prospective demand for having these available in a SELECT format and possibly on SELECTcerts in the future.

06 With regard to Amendment 2 of BS 7671, can SELECT provide any information on expected changes or things we should be aware of?


Amendment 2 of BS 7671:2018 is due for publication on 28 March 2022. This follows Amendment 1 on section 722, electric vehicle charging, which was issued on 1 February 2020 and came into effect on 31 July 2020.

Following a draft for public consultation of Amendment 2, some 1,365 comments were received regarding its publication. These are currently being reviewed by the four JPEL/64 sub-committees and are due for completion in April 2021.

The areas that received the most comments were:

  • Regulation 421.1.7 AFDDs – it is proposed that AFDDs shall be mandated for socket outlet circuits in certain types of installations, namely higher risk residential buildings (HRRB), houses in multiple occupation (HMO), purpose-built student accommodation and residential homes. For all other premises, the use of AFDDs is recommended for socket outlet circuits.

  • Regulation 411.3.3 RCD risk assessment – it is proposed that the option to omit RCD additional protection for socket outlets in certain locations is retained where a suitably documented risk assessment has been undertaken.

  • Regulation 542.1.2.202 foundation earthing – there are proposed changes relating to the requirements for foundation earthing.

  • Regulation 411.3.1.2 protective equipotential bonding – there are proposed changes to help clarify whether metallic or non-metallic pipework requires bonding and whether when required a suitable resistance test can be used to determine if the part is an extraneous conductive part.

  • Other proposed changes – there are proposed changes to the model forms in Appendix 6 regarding the schedule of inspection, the circuit chart and the schedule of test results.

  • Section 443 and 534 regarding Surge Protection Devices (SPDs)

  • The Addition of Part 8 Functional Requirements - including chapter 82 Prosumers Low Voltage Electrical Installations.

At this point, all comments are still under review and no changes have yet been approved for Amendment 2.


SELECT will update Members with any further changes.

Technical Helpline


Got a technical question? Our team of experienced electrical professionals are on hand to advise on every issue. 0131 445 9218

You can also email technicalhelp@select.org.uk

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