Regulations Require More RCDs
Crabtree discuss the implications of the 17th Edition and in particular its effect on the use of RCDs in installations. This is a key area for everyone involved in the wiring of domestic properties so Crabtree have put together a Q&A article which will clear up many of the areas likely to pose problems for installers.
The 17th Edition of the IEE Wiring Regulations, BS 7671: 2008 was issued on January 1st 2008 with the intention that it will take effect on 1st July 2008. Until the end of June 2008, installations can be completed to either 16th or 17th editions, but after this six-month transition period, every electrical installation will need to be designed, installed, inspected, tested and certified according to these new regulations.
The 17th Edition is restructured compared to the present 16th Edition and includes changes necessary to maintain technical alignment with Europe and adopts the IEC numbering system with many of the chapters rewritten. Here though we will be looking at only one of its most significant differences; the requirement to use RCDs on many more circuits than currently specified under the 16th edition.
The 17th Edition differentiates between installations depending on the user. For example, the regulations talk of “installations not under the supervision of skilled or instructed persons” and “socket outlets for general use by ordinary persons” This type of installation requires “Additional Protection” by use of 30mA RCDs on many circuits that have not previously needed protection by RCDs.
The following questions and answers should help give some insight into where you will now need to use
RCDs in new domestic electrical installations for 2008 and beyond.
Will every socket outlet now need RCD protection?
Under the 17th edition, all socket outlets up to 20A rating and intended for general use by ordinary persons should be protected by 30mA RCDs whether on the ground floor of a house or the top floor of a high-rise apartment block.
Are there any changes to the rules relating to bathrooms and showers?
All circuits in a room with a fixed bath or shower should be protected by one or
more 30mA RCDs.
Do the new regs say anything about protecting cables?
All cables buried beneath the plaster surface of a wall or partition (at less than 50mm and without earthed mechanical protection) and all cables concealed in metal stud partitions (common in new builds) should be protected by 30mA RCDs.
Are there any provisions to stop on RCD tripping and taking out the whole installation?
Installations should be divided into circuits, as described in Chapter 31, so as to take account of the danger and inconvenience caused by a single fault – e.g. the de-energising of a lighting circuit. In addition, installations incorporating RCDs should be designed and arranged generally to prevent the unwanted
tripping of RCDs.
Considering most domestic installations have two or three socket circuits, a couple of lighting circuits, and a couple of bathroom circuits and, if all of these have been wired in the traditional manner, with twin and
earth cable beneath the plaster surface, its difficult to come to any conclusion other than that every circuit requires 30mA protection as well as protection by MCBs.
Also, as it’s important to ensure that a single fault does not cause inconvenience, danger or other hazards, more than one 30mA RCD will be required. For example, a fault on the shower should not plunge the bathroom into darkness at the same time. There are many types of property to consider from houses to bed-sits to multi-storey apartments; each will require its own design considerations.
There are many types of equipment to consider too. Some circuits can be grouped together onto one RCD as installers do at the moment in a split load board, but other items may now require a dedicated supply, such as smoke alarms, burglar alarms, warden call, door entry systems etc.
The good news is that Crabtree offer a variety of consumer units and devices that will help the designer and
the installer meet these new regulations. To help electricians provide their customers with the correct protection as defined by these new regulations, Crabtree has issued a consumer unit selection leaflet, showing the outgoing configuration of all relevant consumer units. This includes a new High Integrity
Dual RCD split load unit, using two RCD protected sections with outgoing ways dedicated for High Integrity Circuits using 30mA RCBOs.
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