Technical Article

Now We Are Seventeen!

[photograph of group of RCD/RCBOs] The 17th Edition of the IEE Wiring Regulations has at last been finalised and we have a brief period of respite until it comes into force in the middle of the year. But are the new regulations a positive step and what will electrical contractors need to do to address them? Moeller Electric’s Colin McAhren airs his views.

It’s not exactly a great secret that the biggest change introduced by the 17th Edition of the IEE Wiring Regulations is a greatly increased requirement for circuits to be provided with residual current protection which, in practice, means using either RCDs or RCBOs.

For example, all circuits – including lighting – in a room that contains a bath or shower must have residual current protection, as must almost all circuits supplying socket outlets. Only a few socket outlet circuits, such as those used exclusively for the supply of a domestic freezer, are potentially exempt from this requirement and then only if they are pre-connected to an outlet and the cable is more than 50mm below the surface of the wall. More than one condition needs to be satisfied to meet the 17th Edition.

Is this change a good thing? It would be very hard to argue otherwise. The price of RCDs and RCBOs are now lower in price than they used to be. And they are just as easy to fit and use as an MCB, that even if only a few lives are saved, fitting the extra protection required by the new regulations is definitely a worthwhile step.

Of course, there a possible downside in that the wider use of RCDs may result in more nuisance tripping. To a certain extent, contractors can help to minimise this problem by, for example, taking steps to limit the risk of insects and other foreign matter getting into light fittings, socket outlets and the like, but this can never be a complete solution. The problem is particularly acute when an RCD on the incoming supply is used to protect a group of circuits, which is very common practice.

Potentially, this could mean that a transient earth fault on the lighting circuit – by far the most common cause of RCD tripping – could lead to, for example, a freezer being disconnected. If this happens while there is no one at home, the results can be expensive and inconvenient.

In fact, problems of this kind are covered in the 17th Edition, although little attention seems to have been given to the relevant section.

Nevertheless, the intention of Regulations 314.1 and 314.2 is quite clear, since they state, “Every installation shall be divided into circuits as necessary to avoid danger and inconvenience in the event of a fault, take account of danger that may arise from failure of a single circuit such as a lighting circuit, reduce the possibility of unwanted tripping of RCDs etc.” and “Separate circuits to be provided for parts of the installation that need to be separately controlled in such a way that those circuits are not affected by the failure of other circuits.”

What does this mean in practice? It’s up to individual specifiers and installers to interpret the regulations, of course, but it seems apparent that the best way to meet the requirements mentioned is not to use RCD incomers, but to use RCBOs on most, if not all, of the outgoing circuits.

In fact, there are other reasons to prefer this approach. It’s often forgotten that electronic equipment – such as computers, printers, televisions and hi-fi systems – almost always incorporates a mains filter that produces earth leakage current even when it’s working correctly. This can amount to as much as 3 or 4mA per device.

If several devices of this type are fed from a consumer unit with only incoming RCD protection, it’s not long before the leakage currents add up to very close to the tripping current of the RCD. In this situation, regular nuisance tripping is virtually inevitable. Feeding individual circuits with separate RCBOs is, once again, the answer.

In order to satisfy the new regulations, contractors will, of course, have to make changes to their current practices. One of the most significant is likely to be the move away from split-load consumer units, and the adoption, hopefully, of RCBOs rather than MCBs as the most common form of protection device.

This change in emphasis on protection products has generated concern that the introduction of the new regulations, currently planned for June 2008, will lead to a shortage of RCDs and RCBOs, which will, in turn, provide manufacturers with an opportunity to increase their prices. These concerns are, however, unfounded – certainly in the case of Moeller Electric, which will continue to offer both RCDs and RCBOs at very affordable prices.

The introduction of the 17th Edition of the IEE Wiring Regulations hasn’t exactly come as a surprise. The new regulations have been under discussion for years, and the content, while not completely finalised, has been clear in outline for well over a year. Manufacturers of protective devices have, therefore, had plenty of time to prepare themselves for the changes and to ensure that they have adequate stock of, and manufacturing capacity for RCDs and RCBOs.

As for price increases, with no product shortages expected, increased demand is in the long run likely to ensure that prices at least remain steady and quite possibly fall.

There is, however, a need to sound a note of caution. The rapid growth in demand for residual current protection devices will be seen as an opportunity for counterfeiters and those who import cheap devices of uncertain performance and reliability. It’s worth bearing in mind that a contractor who knowingly uses such a device may well be prosecuted if its use results in accident or injury.

The way to avoid this problem, of course, is only to buy devices with well-known and respected brands, and only to source them from an established supplier. The old maxim, “if it looks too good to be true, it probably is” most certainly applies in this case. Never forget that residual current devices are not fitted just to satisfy the regulations, they’re there to protect lives. Penny pinching just isn’t acceptable!

The changes that will be introduced by the 17th Edition of the Wiring Regulations are progressive and, without doubt, they are to be welcomed by electrical contractors and property owners alike. Once the inevitable transition period is over, they are unlikely to cause problems with contractors and, indeed they may even create opportunities for updating existing installations.

It’s important, however, for contractors to bear one important point in mind – safe, dependable installations will always depend on using reliable, properly tested products from an established supplier, of which a good example is, of course, Moeller Electric.

This page last updated: 16 September 2008