17th Edition - New Edition makes perfect sense
The new 17th Edition Wiring Regulations are almost upon us and from 1 July all new 
installations must comply. However, as Graham Cass of WF Electrical explains, there is no need for concern as the primary impact of this Edition is easily complied with
Those of us old enough to remember the debacle over the introduction of the 15th Edition Wiring Regulations, with its three year delay from 1982 to 1985, confusions and, for many, sheer incomprehensibility, naturally tend to shudder a little at the thought of new "Regs" coming. It has to be remebered however, that the introduction of the 16th Edition , while hasty, was in fact reasonably cleanly implemented.
One of the problems surrounding the introduction of the 15th Edition regulations back in the eighties was the question of how to accommodate the stringent IEC voltage requirements. One of the 17th Edition's primary remits has been to harmonise UK wiring regulations with the IEC and the rest of Europe. In effect, the new version of BS 7671 (IEE 17th Edition Wiring Regulations) has been produced to include the changes necessary to maintain technical alignment with IEC (International) and CENELEC (European) harmonisation documents (HD 384). In short, the new regulations have been renumbered; restructured; new regulations have been added; and some existing regulations removed.
While trade bodies such as the NICEIC and the ECA provide an invaluable role in assisting contractors in complying with new Wiring Regulations, it is also, WF Electrical believes, beholden on electrical wholesalers, stockists and manufacturers to simplify the regulations as far as possible. To this end, contractors will be able to consult WF for advice, while manufacturers - such as MK Electric, which has produced some very clear and simple guides - are also a source of useful, practical advice.
The most fundamental change to the regulations that directly affects electrical contractors and installers relates to safety and the use of Residual Current Devices (RCDs) and Residual Current Circuit Breakers with Overcurrent Protection (RCBOs). The required increase in use of these effective devices makes perfect sense and is designed to increase safety.
Previously, RCDs have only been required to protect socket outlets for use outdoors, where adequate disconnection times cannot be achieved, and also in special locations such as boats, caravans and so forth. This is where the fundamental change comes with the introduction of the 17th Edition.
The term ‘additional protection' crops up time and again within the new 17th Edition. The use of RCDs is recognised as a means of providing additional protection in the event of failure of the provision for basic protection (possibility of electric shock without a fault), as an additional means of fault protection (possibility of electric shock from a single fault), and also, significantly, to protect against carelessness by users.
In technical terms, if an RCD is used to provide Additional Protection it must then meet the requirements of Regulation 415.1.1. That is, the RCD must have a rated residual operating current not exceeding 30mA, and an operating time not exceeding 40ms at five times the rated current. Again, reputable wholesalers should, as WF will, provide advice on selection of appropriate devices if required.
The 17th Edition refers to various applications and installations which require "additional protection" by the means of RCDs. The first of which is found in Regulation 411.3.3, where additional protection is required for socket outlets with a rated current not exceeding 20A, that are for use by "ordinary persons" (for example, the owner or occupier) and intended for general use and also mobile equipment with a current rating not exceeding 32A for use outdoors. However, this regulation doesn't apply for sockets being used by "skilled persons" (qualified electricians) or "instructed persons" (those under the supervision of a qualified electrician for example). As a practical example, a house being wired by qualified electricians can have temporary sockets for use by the electrical contractors, without contravening the 17th Edition regulations.
A further notable exception is where a specific labelled socket outlet is provided for connection for a particular item of equipment. One example of this would be if facilities or maintenance operatives oversaw an installation, as would be the case in commercial or industrial sites. In domestic installations labelling could be interpreted as socket outlets marked, for instance, ‘fridge', ‘freezer' or ‘washing machine' - their corresponding isolated/console switches being similarly marked.
There are more requirements for additional protection in section 522 - ‘Selection and Erection of Wiring Systems in Relation to External Influences'. A frequently encountered example of this is covered in Regulation 522.6.6 that applies to cables concealed in a wall or partition, at a depth of less than 50mm from the surface - indeed, a common practice in most installations.
Five installation methods are offered for cables at a depth of less than 50mm:
s The cable should incorporate an earthed metallic covering, which acts as a circuit protective conductor (CPC)
s The cable should be enclosed in earthed conduit
s The cable should be enclosed in earthed trunking or ducting
s The cable should be mechanically protected against penetration by nails or screws
s The cable should be installed in a safe zone (i.e. the area within 150mm from the top of the wall or partition, or within 150mm of an angle formed by two adjoining walls or partitions. Check the Regulations for a full definition)
In fact, these considerations are very similar to the 16th Edition. However, the Regulation, 522.6.7, states that where the installation is not intended to be under the supervision of an electrician, a cable installed in within the safe zone, and not complying with the other methods must also be provided with additional protection from an RCD.
Typically, a domestic installation, as well as some commercial installations, would use cables with PVC insulation that are therefore not mechanically protected or incorporate an earthed metallic covering. These cables now require RCD protection.
Irrespective of the depth of the cable, Regulation 522.6.8 requires that a cable is installed in a wall or partition, if the construction of the wall or partition incorporates metallic parts, the installation method must one of the first four listed above or be protected by a 30mA RCD.
Section 701 concerns rooms with a bath or shower. It is now requiremed under 701.411.3.3 that additional protection must be provided for all such circuits by one or more RCDs.
As well as obvious items such as electric towel rails and electric showers, this regulation also applies to lighting. Although all of these areas require RCD protection, the requirements of Regulation 314.1, ‘Division of Installation', must also be taken into account. When installing the circuit protective arrangements, Regulation 314.1 states that every installation shall be divided into circuits as necessary to:
s Avoid hazards and minimise inconvenience in the event of a fault
s Take account of danger that may arise from the failure of a single circuit such as a lighting circuit
s Reduce the possibility of unwanted tripping of RCDs due to excessive protective conductor currents produced by equipment in normal operation
This means the whole installation cannot be protected by a single RCD, as in the event of a fault, power will be lost to all circuits potentially causing hazards, inconvenience and danger. In other words, multiple RCDs should be installed to protect the outgoing circuits and should also be split across the RCDs. Alternatively, the installation of suitable RCBOs could be used to protect individual circuits.
A practical example of the above might be a split arrangement with ground floor and first floor lighting circuits protected by separate RCDs. Another example would be that the circuit which supplies the bathroom lighting would be separately protected from that which supplies the electric shower. A fault developing on the electric shower circuit would then not affect the lighting circuit.
In conclusion, it is of course vital for all electrical contractors to become conversant as quickly as possible with the new 17th Edition. There are nuances that must be considered - for example in relation to testing and so forth. However, there is little to fear it seems and the major changes outlined in this article make complete sense and are easy to implement. WF will advise and carries stocks of a very broad range of products to ensure compliance from 1 July.
Share this article with others
Post to del.icio.us
Printed from http://www.electricalreview.co.uk/features/117891/17th_Edition_-_New_Edition_makes_perfect_sense.html
Comment on this article
Skip to comments
We encourage users to analyse, comment on and even challenge Electrical Review's articles, including the one above - '17th Edition - New Edition makes perfect sense'
User reviews and comments that include profanity or personal attacks or other inappropriate comments or material will be removed from the site.
Additionally, entries that are unsigned or contain "signatures" by someone other than the actual author will be removed. We will take steps to block users who violate any of our posting standards, terms of use or privacy policies or any other policies governing this site.