Sweet seventeen

The introduction of the 17th Edition of the Wiring Regulations has meant that the standards that electrical installations adhere to have changed. By July 2008, all new electrical installation work within the scope of BS 7671 will have to comply with the revised Wiring Regulations, and electrical contractors will need to ensure their workforce is up to date in order to fulfil the needs of their contracts.

Although there have been many amendments to the 16th Edition, this has been the most significant overhaul of the regulations since 1992. While the basic principles of the regulations remain, the revised standard includes the changes necessary to maintain technical alignment with European harmonisation documents, changes in design, specification, testing and inspection, and terminology.

Such changes have, understandably, caused some concern among firms, particularly relating to the domestic sector requirements for additional protection by the use of residual-current devices (RCDs), or residual-current devices with overcurrent protection (RCBOs), that will now need to be included in most circuits within dwellings.

Here we will concentrate on changes mainly covered in chapter 41, Protection against electric shock, and chapter 52, Selection and erection of wiring.

Chapter 41: Protection against electric shock

Although many of the regulations are worded differently from the 16th Edition, contractors can be reassured that the requirements themselves have not significantly changed.

The terms ‘direct contact’ and ‘indirect contact’ are no longer used and have been replaced by ‘basic protection’, for protection against electric shock through touching live parts, and ‘fault protection’, for protection against receiving a shock from conductive parts that have become live due to a breakdown of insulation or damage to equipment.

Contractors should be aware that, to meet the requirements in this chapter, additional protection is required by means of RCDs for any socket outlet with a rating not exceeding 20 amps for use by ‘ordinary persons’. These are persons who are not skilled or instructed.

So, rather than applying just to wet environments, such as bathrooms, saunas or swimming pools, as in the 16th Edition, the revised regulations state that any general purpose socket outlet in a dwelling or similar property must now have RCD protection.

Socket outlets rated at a maximum of 20 A and intended for general use by ‘ordinary persons’ must be protected by 30 mA RCDs. External sockets rated up to 32 A must also have a 30 mA RCD.

An exception is permitted for socket outlets for use under the supervision of ‘skilled’ or ‘instructed persons’ – a person with technical knowledge or sufficient experience to enable them to avoid danger while using electricity.

This exception would apply to installations under the control of skilled or instructed persons, such as office, industrial and large retail sites.

Chapter 52: Selection and erection of wiring systems

This chapter includes new regulations on cables concealed in walls or partitions. They also apply the concept of the ‘skilled’ or ‘instructed’ person.

These new requirements now mean all cables concealed within the building fabric – walls or partitions – at a depth of less than 50 mm will need to be protected by an RCD, where the installation is not intended to be under the supervision of a ‘skilled’ or ‘instructed person’.

This new regulation, which particularly affects domestic situations, now requires cables that are buried less than 50 mm into a wall or partition and are not enclosed in earthed metallic covering, nor do they have mechanical protection capable of resisting nails, screws or drills, to be protected by a 30 mA RCD.

They must also be installed in the ‘safe zones’ created by the position of accessories, as previously permitted.

Similarly, cables that are installed in metal-framed walls require a 30 mA RCD or earthed metallic covering.

This means that, for new electrical installations in dwellings where insulated and sheathed cables are concealed within the building fabric at a depth of less than 50 mm and have no earthed mechanical protection, circuits need to be installed within the safe wiring zones and need to be protected by a 30 mA RCD.

The ‘skilled or instructed person’ clause again applies.

Previously, the requirements of the 16th Edition left the responsibility for the use of RCDs to the respective designers and installers of electrical installations, subject to their risk assessment or parameters of the services being supplied and their local environment.

From 1 July, designers and installers of electrical installations will need to consider more carefully appropriate circuit arrangements, protective devices and wiring solutions in order to comply with these new regulations.