RCDs in all their different forms have been around for many years. While professionals in the industry are aware of their capabilities, there is still much confusion surrounding the different terminology used, the types of RCDs available and knowing exactly where and how the technology should be installed. The 17th edition of the IEE Wiring Regulations requires electricians to consider the use of RCDs in a wider variety of new applications, than previous standards have demanded.
The basic function of an RCD is to trip and disconnect the supply of electricity in the event of an earth fault. It does this by detecting the imbalance of currents between the line 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 will provide guidance on how RCDs should be incorporated into new builds.
One example is the requirement for cables concealed in a wall/partition at a depth of less than 50mm. Cables concealed in walls in domestic installations at a depth less than 50mm 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 current 16th edition of the wiring regulations have no requirements for RCD protection. The only exception to this rule is if the cables are enclosed in an earthed metallic covering/conduit or equivalent protection capable of resisting nails, screws or any sharp objects. This is also the case for cables installed in metal-framed walls – a modern and popular construction technique.
Within the revised regulations, 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 RCBOs (residual current breakers with overload protection). An RCBO combines the functions of an MCB (miniature circuit breaker) and an RCD in one unit. They are used to protect a particular circuit, instead of having a single RCD for the whole building.
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, losing all power immediately. By using circuits with individual RCD protection as well as groups of circuits protected by one RCD in combination with one another, the required protection can be provided whilst maintaining continuity of supply to other non-affected zones within the installation.
Educating the consumer
However, it is not just the industry that needs to adapt to the new IEE wiring regulations. Consumers and homeowners must be educated about the technology, as there is a limited knowledge on the operation of RCDs and the additional protection that they can provide for any property. By encouraging a higher level of understanding of the devices, RCDs could help reduce the accident statistics and improve everyday protection against electrical faults.
Control and monitoring are also increasingly important. The most advanced RCDs on the market are capable of using add-on accessories allowing the supply of electricity to be disconnected remotely. Whilst this may be of little use to residential properties, for commercial properties this provides a simple yet effective tool in reducing potential hazards.
Many people think the term RCD applies to just one device, when actually the term refers to a range of devices with different functions and capabilities. Homeowners need to consider the hazards and the protection required before deciding on the technology to invest in. There are currently two main types: the RCBO (as described above, providing earth fault, overlaod and short-circuit protection) and the RCCB (residual current circuit breaker, providing earth fault protection only). The technology is now available in several forms, including portable adapters, RCDs incorporated in socket outlets or plugs, stand alone units for fixed wiring installations, modular units for DIN rail mounting, and a modular unit combined with RCD/MCB units.
The IEE Wiring regulations encourage communications across the industries and enable a more harmonised approach towards electrical protection in buildings. Now, builders, electricians, designers, manufacturers and any other parties involved in building design or construction 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.
- Alan Roadway is product manager for ABB’s Low Voltage Distribution Products business. For more information about the products described in this article email: lv.products@gb.abb.com or use the DPA enquiry service