18th Edition Wiring Regs Preview

by Editor on June 26, 2017

The 18th Edition of the IET Wiring Regulations is proposed to be published in July 2018 and in force in January 2019.

The significant changes from the 17th edition will cover:

  • Protection Against Overvoltage- Lightning and required Risk Assessments
  • Protection Against Fire- AFDDs
  • Heating Cables and Embedded Heating Systems- Documentation and Metallic Grid
  • Energy Efficiency- New Section


18th Edition BS7671

Here’s a preview of those proposed changes included in the 18th edition of BS7671 Regs due in 2018:

Protection Against Overvoltage


Conditions of external influence for lightning – Protection against transient overvoltage (Surge Protection Devices-SPD) would have to be provided where the consequence caused by over-voltage would affect:

  • Human life, e.g. safety services, medical care facilities
  • Public services and cultural heritage, e.g. loss of public services, IT centres, museums
  • Commercial or industrial activity, e.g. hotels, banks, industries, commercial markets, farms.

 Risk Assessment

For all other cases, a risk assessment would have to be performed in order to determine if protection against transient overvoltage is required.

If the risk assessment is not performed, the electrical installation would have to be provided with protection against transient overvoltage.

Smaller Dwellings

An exception not to provide over-voltage protection is included for single dwelling units where the total economic value of the electrical installation to be protected is less than 5 times the economic value of the SPD located at the origin of the installation.

Protection Against Fire


Details will be included for the installation of Arc Fault Detection Devices (AFDDs) to mitigate the risk of fire in final circuits of a fixed installation due to the effect of arc fault currents.

Why Are RCDs Not Enough?

It is recognised that RCDs can reduce the likelihood of fires associated with earth faults. However, whilst RCDs can detect earth faults they aren’t able to reduce the risk of electrical fire due to series or parallel arcing between live conductors. This is because there is no leakage current to earth. Also it is understood that the impedance of a series arc fault reduces the load current, which will keep the current below the tripping threshold of the circuit-breaker and the circuit-breaker may therefore not operate to disconnect the circuit.

Heating Cables and Embedded Heating Systems

Section 753 regs have been extended to apply to embedded electric heating systems for surface heating. They also apply to electric heating systems for de-icing or frost prevention and cover both indoor and outdoor systems for walls, ceilings, floors, roofs, drainpipes, gutters, pipes, stairs, roadways and non-hardened compacted areas (for example, football fields, lawns)


The designer will be required to provide appropriate information about approved substances in the surroundings of the heating units. For wall heating systems (which are more vulnerable than floors and ceilings from penetration) the standard contains additional requirements to protect against the effects of overheating caused by a short-circuit between live conductors due to penetration of an embedded heating unit.

Metallic Grid to Earth

In the case of heating units that are delivered from the manufacturer without an earthed conductive shield, a suitable conductive covering, for example, a mesh metallic grid, with a mesh size of not more than 3 mm for wall installations, shall be provided on site and connected to the protective conductor of the electrical installation.

Harmful Influences

In addition, the IEC standard requires that electric heating systems shall be selected and erected so as to avoid any harmful influence between the heating system and any electrical or non-electrical installations.

Energy efficiency

This is a new section. The draft proposals enable a client to specify the level of energy efficiency measures applied to an electrical installation.

Proposals cover several energy efficient areas, such as electric vehicles, lighting, metering, cable losses, transformer losses, power-factor correction, and harmonics.

Efficiency Class Points System

Installations can also be awarded points for energy efficiency performance levels, for example, transformer efficiency. These points can be added together with points for efficiency measures to give an electrical installation an efficiency class, ranging from EIEC0 to EIEC4, depending on the number of points awarded.

Find more info about the 18th Edition Regs

You can view or download the draft 18th Edition by registering on the BSI website


{ 1 comment… read it below or add one }

EDB Electrical Services April 1, 2018 at 23:37

Excellent article and very exciting changes to the IET wiring regulations. Not long now but not looking forward to having to buy new books

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