Now that the UK electrical industry has finally seen the latest changes to the 17th Edition of the IEE Wiring Regulations (BS 7671), Alan Roadway, Product Manager for ABB's Low Voltage Distribution Products business, explores the new mandatory use of Residual Current Devices (RCDs) and the consequent effects:
Amendment 1 comes into force January 2012
Whilst residual current devices (RCD) have been in use for many years, the new 17th Edition requires electricians to consider the use of RCDs in many more applications than the current standard requires in order to improve building protection.
The basic function of an RCD is to trip and disconnect the supply of electricity in the event of an earth fault in order to prevent electric shock and fire risk. It does this by detecting the imbalance of currents between the live and neutral lines caused by a fault to earth. Drawing attention to the importance of using RCDs in the right context and with the right equipment, the IEE Wiring Regulations provides guidance on how RCDs should be incorporated in new builds.
One example is the requirement for cables concealed in a wall/partition at a depth of less than 50mm in domestic installations. Such cables will need to be protected by an RCD rated at 30mA or below, even if they are in a safe zone. This has implications for lighting circuits, which - under the still current 16th Edition - have no requirement for RCD protection. Note that both 16th and 17th Editions are run in parallel until full implementation on July 1st 2008, after which all new installations, alterations and additions designed on or after 2nd July will need to comply with the new requirements.
The only exception to this will be if the cables are enclosed in an earthed metallic covering / conduit or equivalent protection capable of resisting nails, screws etc. This is also the case for cables installed in metal-framed walls - a very popular construction technique at the moment.
30mA RCD protection for ALL sockets:
Additionally, all socket outlets rated at 20A or below within a domestic building will require 30mA RCD protection*. This means that all ring main circuits from consumer units will either need to be fed from the RCD side of a traditional split load board or have individual residual current breakers with overload (RCBO) ways.
Because the RCD is sensitive to current imbalances, it is not practical to fit just one device to protect an entire house. If a fault develops within one circuit, all circuits would be switched off immediately. By using individual and grouped RCD protected ways in combination with one another, the required protection can be provided whilst maintaining continuity of supply to other non-affected zones within the installation
Much more detail required:
However, this does mean that, for architects, builders and electricians, much more detail must be put into the design and implementation of any new building supply. Now, utility rooms and storage areas will require specific design and consideration based on the devices installed. Bathrooms are under particular scrutiny. The new regulations will require RCD protection for all circuits supplying electrical equipment within Zones 0, 1 and 2 (Zone 3 is being removed). In addition, all cables buried in walls surrounding bathrooms must have 30mA RCD protection - regardless of the points they are supplying. This could have significant implications on the routing of cables to avoid crossing these zones within ceiling voids and adjoining walls.
Many of the changes to the 16th Edition are part of a harmonisation process to create commonality of installation standards throughout Europe and the world. Whilst the 17th Edition sees an increase in the use of RCDs, it is unlikely that the products themselves will change dramatically as they are have been designed and manufactured to the harmonised and 'normalised' European and worldwide standards in any case.
With more regulations to consider, the IEE Wiring Regulations encourage communications across the industries and enable a more harmonised approach towards building. Now, builders, electricians, designers, manufacturers and our clients will all need to be able to discuss the practices required to meet the new regulations and ensure greater health and safety for any building's inhabitants.
*For all socket outlets for use by 'ordinary persons' i.e. a person who is not a skilled or instructed person.