This webinar was arranged by the IET's Electrician EngTech programme in association with Wiring Matters. Electrician EngTech helps electricians gain recognition of their professional competence.
Your questions answered
Would the use of a non-BASEC approved cable be a departure? i.e. SY/YY cable?
Not necessarily. Provided a SY/CY/YY cable is used:
- where it may not be appropriate to use a cable to a recognised standard
- where its strength and capability are not exceeded (examples include: the steel or copper braid in SY and CY cables are not intended to afford mechanical protection, and may not necessarily meet the requirements for a protective conductor for a buried cable; sheaths may not be suitable for use outdoors unless they are UV stabilized; some sheath and insulation materials used for SY/CY/YY are not always suitable for long-term exposure to moisture, such as submersion, etc.)
- where the correct type of cable is selected for the function (some SY/CY/YY cables are intended for auxiliary circuits only, and are not intended to be used for power circuits).
Then the Designer, or person selecting the cable, may use such products, where they are confirmed to provide at least the same degree of safety as that afforded by compliance with the Regulations, in accordance with Regulation 511.2. The use is to be recorded on the appropriate certification, and documentation confirming the safety attached.
Guidance specifically on non-standard cables, including SY/CY/YY types, is provided in Section 7.9 of the IET's On-Site Guide.
VDE cables have less insulation than SWA or similar. But are there no similar cables able to be used in installations such as swing arms? (Without using tri-rated cables and flex conduit, where experience tells me they are not as robust VDE cables).
Your cable selection should consider the External Influences set out in Appendix 5 of BS 7671. One option might be HO7 RNF cables depending on the actual circumstances.
Is it the designer's responsibility to ensure that the installation is carried out to the design?
Ultimately this is a matter of contract, and perhaps who is going to sign the Electrical Installation Certificate.
Where a client's technical team (consultant) provides a brief of expectation to the deign and build provider, is there a requirement for duel design signoff?
Ultimately this is a matter of contract, and perhaps who is going to sign the Electrical Installation Certificate.
Does departure from Regulations include installation methods that are not recognised as well as materials?
It could do. The important thing is the designer has to certify that whatever does not comply with BS 7671 is no less safe than meeting the requirements of BS 7671.
What is the minimum level of voltage that can maim or kill livestock in farms?
It would depend on the type of animal, the current path through the animal and the duration of the shock current. There is no fixed voltage.
Why does a garage (as a detached building) need to have its own separate earthing arrangement (earthing rod), when the supply is coming from the main building?
This is not a requirement of BS 7671, nor of ENA Engineering Recommendation G12/4.
If the outbuilding has extraneous-conductive-parts, then, where PME conditions apply, main bonding conductors in the outbuilding must meet the requirements for main bonding conductors, as must the circuit protective conductor of the sub-main supplying the outbuilding. In some cases, this is cost-prohibitive, and a TT earthing arrangement is used at the outbuilding.
If the outbuilding has no extraneous-conductive-parts, this consideration is unnecessary.
The IET produces Guidance Notes which cover Parts 4 onwards. What guidance is available for Parts 1 and 3?
The Fundamental Principles are set out in Part 1 and the Assessment of General in Part 3. The application of these Parts are covered in many IET Guidance Notes and the Electrical Installation Design Guide.
Are there criteria that help to define what is required to be considered an 'Electrically Skilled Person'?
Electrically Skilled Person' is defined in Part 2 of BS 7671.
As a designer, where there is SY used in the fixed wiring of the installation, and you are carrying out amendments/additions to the installation should you then recommend it be replaced? On an installation where SY cabling has been used in the fixed wiring, what code would you record it as on an EICR?
Not necessarily. Provided a SY/CY/YY cable is used:
- where it may not be appropriate to use a cable to a recognised standard
- where its strength and capability are not exceeded (examples include: the steel or copper braid in SY and CY cables are not intended to afford mechanical protection, and may not necessarily meet the requirements for a protective conductor for a buried cable; sheaths may not be suitable for use outdoors unless they are UV stabilized; Some sheath and insulation materials used for SY/CY/YY are not always suitable for long-term exposure to moisture, such as submersion, etc.)
- where the correct type of cable is selected for the function (some SY/CY/YY cables are intended for auxiliary circuits only, and are not intended to be used for power circuits).
Then the Designer, or person selecting the cable, may use such products, where they are confirmed to provide at least the same degree of safety as that afforded by compliance with the Regulations, in accordance with Regulations 511.2. The use is to be recorded on the appropriate certification, and documentation confirming the safety attached.
Guidance specifically on non-standard cables, including SY/CY/YY types, is provided in Section 7.9 of the On-Site Guide.
Why is a BS88 used for life safety supplies?
It can be found in document TB210 from the Fire Protection Association.
Should we as a designer try to influence intake positions? The DNOs have been getting new directives to be more proactive about sustainability. I recently had an unexpected result getting free 3 phase into a domestic property for a heat pump. What leverage can we apply realistically?
Early discussions with the DNO can be fruitful and reading their published guides to supplies online is recommended.
Is the max volt drop not fixed at 4%?
No. See Appendix 6 of BS 7671.
How much future-proofing would you typically recommend for consumer units/distribution or cables to sub mains?
It would depend on the size of premises and the possible load growth over the life of the installation, as well as the requirement from the client.
BS 7671 is increasingly being directly referred to by legislation (e.g. ESQCR, private rented housing etc) but these references are to a fixed and often outdated version of BS 7671. Is it a safe assumption that designing to the latest version of BS 7671 will in all cases satisfy the legal requirement to meet an earlier version, or might we be obliged to design to an outdated version of BS 7671? Or even, considering all applicable legislation along with customer/insurance requirements, to come up with a design that satisfies two or more different versions of BS 7671 simultaneously?
All standards undergo revision, and these are usually addressed by contract variations, to be agreed or rejected by the Client. Most standard forms of contract include procedures for this.
Risk assessments should be reviewed when standards change, and CDM risk assessments are no exception.
Is the 20% allowance for the bus bar or distribution board?
It depends firstly on the requirements of the client or the client's representative who may specify what spare capacity is required. Then what about load growth over the life of the installation? How much capacity is there in the local DNO network? It is good practice to allow something like 20% spare capacity on the supply, on the distribution circuits (cable or bus bar) and 20% spare ways in distribution boards, and agree this with the client.
Purely for design implications – AFDD’s becoming mandatory on installations undertaken after March 2023 – what is the case for installations undertaken (and designed) before this date which are completed after this date?
There are no guarantees as yet, that any changes to BS 7671 proposed in the Draft for Public Comment of Amendment 2, will actually be part of Amendment 2:2020.
All standards undergo revision, and these are usually addressed by contract variations, to be agreed or rejected by the Client. Most standard forms of contract include procedures for this.
Now that the UK is out of the EU, have the former colour-codes become acceptable alternatives again?
This is highly unlikely. Colour codes are actually harmonized via BS EN 60445, not BS 7671, and the changes proposed in the Amendment 2 DPC are as a result of changes in BS EN 60445:2017.
BS EN 60445 aligns with IEC 60445, and is an international standard.
EMC – what is the meaning of emission and immunity? Can you please explain in very simple steps?
When electric currents travel in any conductor, electrostatic and electromagnetic fields are generated.
When the current changes, such as with alternating current or harmonics, the electrostatic and electromagnetic fields emitted from conductors also changes. The resulting fields travel as electromagnetic radiation, and these are known as radiated emissions.
Current fields may also travel down conductors. These are known as conducted emissions.
Where emissions create unwanted interference, or ""noise"", we also call these disturbances.
Equipment can be made with a tolerance to disturbances (noise or emissions) – we call this the level of electromagnetic immunity.
With reference to reg group 422.2.2.1 concerning the term 'escape routes' and refence to use of cables to BS EN 60332-3. Should such cables be used throughout high rise buildings? Are such cables readily available?
Yes cables are readily available. The Fire Risk Assessment, Fire Strategy and BS 7671, BS 8519 and other standards will determine what is required. There are changes proposed in the DPC for BS 7671 AMD 2 so we must wait to see what the outcome is when AMD 2 is published.
Where do we stand with higher-order frequency issues that are above the standard harmonic G5/5 frequencies? Will there ever, do you think, be standards to cover these, as often they can still cause issues with installations, usually when low harmonic VSD's are installed?
There are already requirements in BS 7671 concerning harmonics. The problem of exporting harmonics to the grid will increase with local generation and more electronic controlled devices, switch mode power supplies and VSDs. We suspect the need for harmonic filtration will increase.
Whose responsibility is it for the design of the connection of a lightning conductor to the MEB? And if a lightning conductor is connected to the structural steel of a building, how to you take into to account this bonding in your calculations?
This will depend on the responsibilities for a particular contract. This may not be the same for every job, especially where different organisations are responsible for the electrical installation and the LPS. The design should take into account the requirements of both the electrical installation (to BS 7671) and the lightning protection system (to BS EN 62305 series). It may be necessary for the electrical designer/contractor and the LPS specialist or contractor to discuss the interface to ensure that both standards are met by the designs.
Such interface work is also required in respect of SPDs and overvoltage control, as well as earthing, to meet the various requirements of BS 7671.
Is the training of the Building Management Team on the O&M of installation part of the job, even though O&M Manuals and drawings contain all information?
Fundamentally, this depends on the terms of the contract, and the complexity of the installation. Complexity doesn't always relate to size, for example, there are hazards not covered in "standard electrical training" for installations with control systems – including SMART installations. Not all electricians and technicians have been trained with this type of system, so certainly if there is an O&M organisation they may well need training on certain aspects.
Who is responsible for producing the Electrical Installation Certificate that requires a design signature?
This is clearly stated in Regulation 644.4 of BS 7671 – joint responsibility of the person or persons responsible for design, construction and verification of the installation (or addition or alteration). Ultimately, though, it may be a matter of contract for an individual project, as to which legal person or persons are considered to be responsible for the design, construction and verification.
Is there reference for demand and diversity factor as BS?
Diversity is mentioned in BS 7671. The IET On-Site Guide and IET Guidance Note 1: Selection and Erection also provide guidance for calculating diversity.
Are there any regulations/guidelines stating how much capacity must be spare in containment?
No. However the IET On-Site Guide provides guidance on the sizing of conduit and trunking so that cables may be easily and safely drawn in. Good engineering judgement would dictate that spare capacity in containment would permit later alterations and additions.
When working on a long-term new-build project and the Regulations change during the construction phase, are there any statutory obligations on the designer to update?
All standards undergo revision, and these are usually addressed by contract variations, to be agreed or rejected by the Client. Most standard forms of contract include procedures for this.
Risk assessments should be reviewed when standards change, and CDM risk assessments are no exception.
If a designer decides an installation method and the contractor on site installs it in a different method, can the designer refuse to sign the design certificate?
This is a very broad question, although interestingly the person working for the Contractor also becomes a Designer under CDM Regulations. See also answer to question 39 below.
Are there any specific qualification or accreditations that need to be held by a designer?
BS 7671 requires that the designer be an 'Electrically Skilled Person' and that definition can be found in Part 2 of BS 7671. No specific qualifications are required, however, City and Guilds offer the Level 4 2396 design course.
How is legislation likely to change with respect to EV charging, particularly with high output (>20kW) units being installed en masse?
We do not know of any proposed legislation in respect of EV charging. The government have indicated that fossil-fuelled vehicles will be phased out by 2030.
Do you now lower over current settings to reduce potential arc energy?
Energy let through I2t will depend on the impedance of the supply and the protective devices is a circuit.
Protective devices will limit energy let through. For circuit breakers to BS EN 60898 they have specific maximum let through Classes. Manufacturers publish let through data graphs for their specific devices. It may be necessary for designers to verify the thermal withstand of cables is sufficient for the energy let through.
You mentioned sprinklers being protected by BS 88 Fuses. Is this from BS EN 12845:2015? 10.8.2 Electricity supply – The fuses in the pump controller shall be of high rupturing capacity, capable of carrying the start current of the sprinkler pump for a period of no less than 20 s.?
Yes. Also the Fire Protection Association document TB 210.
Is diversity 60% for dwellings and 80% for commercial/industrial premises?
It is not as simple as that. It depends on the connected loads and how they are used. The IET's Guidance Note 1: Selection and Erection and the IET On-Site Guide provide some useful guidance.
What value of Power Factor is to used at the design stage if the actual value is not known?
There is no substitute for manufacturer's data. For an outline draft design, a designer can use their knowledge and experience and use an estimated figure until they obtain the required data.
In the split of responsibility between designer and installer; how does the Regulations see the responsibility of the designer to check that the installation is in line with design?
This depends on contractual arrangements, but don't forget that an Electrical Installation Certificate should be signed by the person responsible for the design – so the person signing that should.
It is a very good question - because if the design drawings are not 'as built', or a key safety feature such as a point of isolation has been omitted, and not reflected in the CDM risk assessments, someone should expect to be held to account in the event of a safety incident further down the road.
If you're allowing for an EVC charging unit, do you need to notify the DNO to accommodate resilience into their infrastructure?
Yes, in all cases. Where the maximum demand of the installation exceeds 13.8 kVA, or will exceed 13.8 kVA after installation of EV charging equipment, the notification must be made in advance to check the supply capability. For maximum demand up to 13.8 kVA, the notification is done within 28 days of the installation. See Section 11 of the IET Code of Practice for EV Charging Equipment Installation, 4th Edition.
Outside a domestic residential property are you relying on manufacturing data when calculating diversity or the organisation commissioning the work? (Or a combination of both?) And should it be documented within the documents presented to the Client?
Selectivity is a requirement of BS 7671. See section 536.
Surely 20-25% goes up to 50% when considering battery charging on domestic installations?
Maybe. It depends firstly on the requirements of the client or the client's representative who may specify what spare capacity is required. Then what about load growth over the life of the installation. How much capacity is there in the local DNO network. It is good practice to allow something like 20% spare capacity on the supply, on the distribution circuits (cable or bus bar) and 20% spare ways in distribution boards and agree this with the client. For EV charging it may be necessary to use load curtailment to limit maximum demand.
AFDDs comes up on every project and mandatory provision appears confusing with Designers, what is the panel's view on this protection?
AFDDs are not mandated in the current edition of BS 7671 they are only recommended. The DPC for Amendment 2 to BS 7671:2018 requires them to be mandatory. That said we do not know what the outcome will be of the result of the public consultation until the Amendment is published.
Looking at some of the fast chargers electric car chargers on the market would you expect an increase of 3 phase supply into residential premises? I have been asked to fit one recently but it means a complete new supply from the DNIO/DSO.
Some DNOs are already offering three-phase supplies to new build housing developments.
For electric charging loads for domestic would you apply a diversity? Depending on the size of the charge i.e. 3kW, 7kW etc.
Diversity is difficult to apply in smaller installations, but is no longer prohibited for EV charging installations (the prohibition having been removed in Amendment 1:2020 to BS 7671:2018). However, if load curtailment is used, this can be taken into account. Load curtailment was discussed in an earlier webinar. You can view this on-demand.
Do you have to notify the local DNO that you intend to install an EV charging point in a domestic property?
Yes, in all cases. Where the maximum demand of the installation exceeds 13.8 kVA, or will exceed 13.8 kVA after installation of EV charging equipment, the notification must be made in advance to check the supply capability. For maximum demand up to 13.8 kVA, the notification is done within 28 days of the installation. See Section 11 of the IET Code of Practice for EV Charging Equipment Installation, 4th Edition.
Which Standards do you have to follow to ensure access of consumer units by persons with limited mobility?
See BS 8300-1 and BS 8300-2, along with the building regulations accessibility guidance publications for the particular devolved nation. It may also be prudent to consider a means of limiting access to unsupervised young children whilst facilitating the accessibility requirements. The height recommended in Section 3.1.3 of the IET's Electrician's Guide to the Building Regulations is 1350-1450 mm above finished floor level.
Is the voltage drop from the transformer or intake position inside the building?
The total volt drop is from the origin of the installation to the point of use.
The webinar mentioned BS88 fuses to be used for sprinkler pumps, could MCCBs be used instead?
It can be found in document TB210 from the Fire Protection Association.
What is the maximum life span of supply SWA cables, beyond which they must be replaced with new ones?
This depends on the construction of the cable, and its installation conditions. For example, some manufacturers of PVC sheathed and insulated SWA that is subject to regular or long-term immersion quote much lower service life than the same cable installed in dry conditions.
Buried cables – where do we stand with using alternative BICC data? The tables within BS 7671 for buried cables seem to represent the worst-case solution?
The ratings for cables in BS 7671 are to be found in Appendix 4. Appendix 4 is 'Informative' so does not have to be complied with if a designer, using his/her engineering judgement, decides on an alternative solution. BICC data can be found in some proprietary software.
Which reference should we follow for DNO requirements?
Individual DNOs publish their own requirements. In addition, see the Distribution Code Annex 1 and Annex 2 documents, available from www.dcode.org
Are there requirements about copper loss of cables in design?
Yes, see Appendix 17 of BS 7671, and BS HD 60364-8-1.
The webinar focus has been on regulations; would you agree that any designer should also take heed of Codes of Practice, Professional Body Guidance Notes, Industry good Practice etc.?
Definitely, this is a good point. The only issue to watch out for, is that industry guidance and Codes of Practice (and similar) may not be updated at the same pace as the relevant standards. However, the same also holds true of some standards that reference other standards.
Which discrimination survey would you recommend?
Discrimination' is now termed 'selectivity'. Selectivity is a requirement of BS 7671. See section 536.
With regards to the running temperature of cables, if Amtech and similar software is not available, how do you calculate the running temperature of a cable?
Very difficult to do without software as the running temperature will depend on the type of cable, the installation method and rating factors.
Manufacturers do publish cable data which may be of some help.
What considerations should be given if replacing a BS 88 Panel board with an MCCB Panel board?
In short an awful lot. Things like fault current rating, overload and short circuit protection, achieving ADS for circuits connected to the panel board, physical size, cable entry, cable terminations etc.
Could the fire pump situation be simply put as the fire pump must continue to work to destruction if required to save the building?
Yes, the general view is if the building is already on fire you want the fire pumps to continue running to destruction if necessary.
A cat 2 defect on an EICR needs urgent remedial action. Any views on the definition of urgent in this instance?
This will depend on a particular defect, and the conditions in the particular installation. For example, a damaged cable sheath is not necessarily an immediate hazard, providing conductor insulation is intact, but a further impact could make it an immediate hazard. This is a matter for the relevant duty holder to assess according to the Electricity at Work Regulations?
Which fire standard stipulates BS88 fuses for safety services?
This can be found in document TB210 from the Fire Protection Association.
I recently visited a farm building and found T&E cable had been installed for a new socket outlet. I recommended replacement with a cable method that gave physical protection. When the client contacted their installer, they said nothing was wrong and would not change the cable. Where do they stand?
With the given information it is difficult to say. The design should have considered the External Influences as listed in Appendix 5 of BS 7671. On a farm there will nearly always be the presence of rodents and rodents love chewing on PVC to keep their teeth sharp and short. Ask the contractor for the design information, CDM 2015 requires them to supply it, and ask what considerations were given to External Influences? Assuming the contractor has supplied an EIC for his/her work what have they put against 8.2 of the inspection schedule?
Is it true that the sheath on SY cable is mostly not UV stable and will deteriorate early when installed outside? External influence & conditions.
Not necessarily. Provided a SY/CY/YY cable is used:
- where it may not be appropriate to use a cable to a recognised standard
- where its strength and capability are not exceeded (examples include: the steel or copper braid in SY and CY cables are not intended to afford mechanical protection, and may not necessarily meet the requirements for a protective conductor for a buried cable; sheaths may not be suitable for use outdoors unless they are UV stabilized; Some sheath and insulation materials used for SY/CY/YY are not always suitable for long-term exposure to moisture, such as submersion, etc.)
- where the correct type of cable is selected for the function (some SY/CY/YY cables are intended for auxiliary circuits only, and are not intended to be used for power circuits).
Then the Designer, or person selecting the cable, may use such products, where they are confirmed to provide at least the same degree of safety as that afforded by compliance with the Regulations, in accordance with Regulations 511.2. The use is to be recorded on the appropriate certification, and documentation confirming the safety attached.
Guidance specifically on non-standard cables, including SY/CY/YY types, is provided in Section 7.9 of the On-Site Guide.
Is there a requirement within the Regulations for segregation of dual power supply cables (3 phase supplies)? I.e. a segregation to avoid mechanical damage leading to loss of both supplies.
This is definitely a requirement in some other standards, see for example Clause 37.2.3.3 of BS 9999 regarding primary and secondary supplies for fire protection systems, and similarly Clause 6.3.2.3 of BS 9990 for the primary and secondary supplies (where used) for dual electric wet fire mains pumps.