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Proposed changes to the wiring regulations - BS 7671: 2018

11 July 2017

Proposed changes to the wiring regulations include a reduction in the energy consumption of electrical installations. If the proposal is accepted it could result in the specification and installation of larger diameter power cables. Doug Gracias explains why change is for the better.   
The 18th edition of the Wiring Regulations, aka BS 7671: 2018, is now available as a Draft for Public Comment on the British Standards Institution’s website. The draft is an opportunity to see the proposed content of the revised wiring regulations ahead of publication and to have your say about the changes.
One of the proposals is the addition of a new section, Part 8. This has been introduced to reduce the energy consumption of electrical installations. It is based on the International Electrical Commission’s new standard IEC 60364-8-1 Low Voltage electrical installations Part 8-1 Energy Efficiency. 
The new section covers several energy efficiency areas including limiting the voltage drop within an installation in order to reduce power losses in the wiring system which are evident as heat.
As the UK’s largest cable manufacturer, Prysmian know that the simplest way to bring down power losses is to reduce the voltage drop and to use a cable with a larger cross-sectional area of conductor. The document says the decision on whether or not to increase the conductor size “shall be made by assessing the savings within a time scale against the additional cost due to this over-sizing”. In other words, the reduction in power loss from increasing the cable’s conductivity should be higher than the additional cost of the cable over the lifetime of the installation. 
If, for example, a long run of cable is supplying a constant high load it may well be more cost effective for the cross-sectional area of the cable to be increased in order to reduce power losses. For that reason, the use of the term “over-sized” is not appropriate in this instance. If it is more cost effective over the lifetime of an electrical installation to use a copper conductor with higher conductivity then it is not “over-sized” but optimally sized. A more appropriate term would be “upsized”.
There will, of course, be an increased cost for the additional copper in larger conductor cables when compared with traditional ‘minimum sized’ solutions, as well as accessories and supports, but aside from that installation costs will be broadly the same for new build installations, assuming the same sized conduit or cable tray are still appropriate for the larger diameter cables. 
In addition to reducing power losses there are some other benefits to be had from cable “upsizing” including increasing the cable’s capacity, which may help future-proof the system and also reduce heat emissions from the wiring from harmonic currents. And, because an “upsized” cable will generate less heat, there will also be energy savings, albeit minor ones, from reducing the speed of cooling fans and perhaps even the size of building’s air conditioning system.
Other changes proposed in the Draft 18th edition of the Wiring Regulations include:
Redrafting the section relating to protection against transient over-voltages of atmospheric origin, such as lightning strikes, to ensure protection is in place mitigating against the risk of fire caused by arc fault currents in electrical equipment and
Extending the scope of the section on embedded electric heating systems for indoor and outdoor surface heating, such as those for de-icing or frost protection.
The Wiring Regulations apply to the design, erection and verification of electrical installations in commercial, residential, public and industrial premises along with infrastructure and even caravans. 
To comment on the new standard before 23 August 2017 click here
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