Survey and Test

ISO 50001 and BS7671

What are the energy efficiency requirements for the IET wiring regulations?

By Lydia Newman and Stanley Rayfield


The new 18th Edition of the Institution of Engineering and Technology (IET) wiring regulations (BS 7671:2018) has been in force since January 2019.

Energy efficiency appears within the 18th edition’s 64 new pages for the very first time. These are set out within appendix 17. Aside from the electrical contracting industry, appendix 17 will be of particular interest to organisations that operate an ISO 14001 environmental or ISO 50001 energy management system and therefore need to be aware of their compliance obligations.

Design: What must be considered?

Consideration of energy performance at design stage is an essential component. The load profile should be determined, for example, by being distinguished over a period of at least 24 hours, whether demand for energy is passive or active. For example, in a supermarket, if an escalator would only be active and require energy during occupancy times, the load profile could otherwise be considered passive. Similar could be true of an active ventilation system that uses passive, free cooling to purge the building of heat at night.

With knowledge of when energy is required, it is important to assess where the energy will come from. In order to make optimum use of renewable energy, the designer must also be aware of the type of local generation available. For example, solar energy, wind power, hydroelectric etc. This will reduce the total losses in the public electricity network.

Furthermore, choosing electrical components with care is an important consideration. For example, if you choose an AC induction motor then surplus energy is given off in the form of heat when used at less than full-load settings. This can be counteracted by choosing products with high efficiency, for example being graded IE2 (high efficiency), IE3 (premium efficiency) or IE4 (super premium efficiency). The installation of wiring systems must also be efficient and reduce energy losses by considering power factor correction and by limiting the voltage drop.

It is important for the designer to really understand the user needs in order to ensure that energy is not wasted on impractical design features. Being informed of the user’s energy needs leads to an opportunity for energy to be rationed as a consequence of load shedding. The user can make a judgement whether a certain zone does not need to consume energy at a particular time of day; the energy can then be cut off in that zone when convenient. This could be described as a controlled blackout to reduce the risk of unpredictable future blackouts throughout the building.

Reducing energy loss

Engineers, designers, heating engineers and builders alike can benefit from the guidance of appendix 17, simply by making intelligent decisions with regard to establishing zones and determining which energy usage is required within those zones. Zones might be based upon different activities such as, lighting, heating, ventilation, or cooling and those familiar with SBEM modelling for Part L of building regulations will see the similarities.

For instance, heating profiles may allow for the creation of heating or cooling zones within a building, or zoning for lighting may take into consideration the level of natural day light, which could lead to separate controls where areas in close proximity to windows give less need for artificial light.

An understanding of thermal performance of a building could be another consideration, such as how the thermal mass of the building could aid either heating or cooling, leading to some simple decisions such as location of heaters. For instance, avoiding external walls for the placement of room heaters in favour of siting on an internal wall can use the capacitance of the building fabric to store and later release heat, rather than to lose heat through the exterior walls.

Why is it important to analyse data?

Organising wiring systems in zones makes measuring and monitoring energy efficiency more accessible. During installation there must be provision to document energy consumption at numerous significant points throughout the building or process. These measurements must be taken with accuracy and precision for later analysis.

It should be possible to measure total consumption for each hour of each day in kWhs and should be collected and stored somewhere accessible to the user for at least one year. The principle here is that ‘what gets measured gets managed’. It is an established principle that metering is the first step to reducing energy consumption and by extension, giving a method for future improvements to be monitored.

In addition, this gives a mechanism to easily collect data towards annual or periodic reporting, such as SECR (Streamlined Energy and Carbon Reporting) or ESOS (Energy saving opportunity scheme). Both provide government with data to show progress in line with the Clean Growth Strategy and NetZero.

It’s worth noting also that metering has already been a mandatory feature of certain projects or building under Part L of building regulations and the Heat metering regulations – appendix 17 will expand its use further.

What can you implement into your scheme to maximise energy efficiency?

Energy efficiency can be maximised by locally sourcing energy. Energy sensors can further identify where energy efficiency could be improved and should be the same class as the energy performance and monitoring devices. Forecasts concerning weather and occupancy can lead to improved energy performance. And data logging will provide us with historic data that can be employed to determine future energy demand. An accumulation of years of data can depict a diagnostic trend.

Lighting is responsible for a significant level of energy consumption, therefore it is important to take control and only use it when needed. This action can be aided with the use of brightness controls, dimming controls, light sensitive switches, movement detectors and timed switches.

The energy performance of heating, ventilation and air conditioning (HVAC) can be maximised by enforcing environmental controls and contemplating which HVAC equipment will be most advantageous for energy performance in terms of the installation, usage and structure.

In terms of reducing volt drop, it could be worth evaluating potential savings from reducing energy losses by expanding the cross-sectional area of conductors, despite the initial installation costs.

The circuit length within the building is also dependent on where the power source is located. If this is positioned optimally then the circuit length is reduced, and the electrical infrastructure optimally installed.

How could appendix 17 benefit your business?

If you decide to use energy efficient products and an energy efficient process, you will save money on energy bills as well as reducing your business’s carbon footprint.

Appendix 17 mentions that tariff structures are to be considered within your design. Many suppliers can offer lower energy rates during off-peak times if a sufficient energy storage system is installed.

This will have a positive impact on air quality as this will allow generators throughout the UK to even out their electrical load as there will be a decreased energy demand during the day and less energy wasted at night. Could this be applicable to your project or company?

It may also allow electrical contractors to become advanced in this field; ahead of when these advised regulations become compulsory, enhancing a contractors business’ reputation as a commendable contributor towards net-zero targets.

Is energy efficiency compulsory?

Energy efficiency is currently present in appendix 17. As an appendix, it is therefore only observed as guidance and is not obligatory. However, with regard to the Government’s Clean Growth Strategy, it is no surprise that in future upgraded editions of the IET wiring regulations intends to develop energy efficiency as a mandatory requirement. Energy efficiency will become part 8 of the IET wiring regulations.


It is clear that the Clean Growth Strategy has had an impact on the IET regulations and although energy efficiency is only currently on an advised level we can take this as an opportunity to build our understanding of which wiring systems will work most efficiently in a range of circumstances. It is promising to know that in the near future it will become mandatory to take energy efficiency into consideration in an indirect way in terms of local production and storage of energy, as well as direct ways by being mindful of how to install energy efficient systems and products while reducing energy losses.