The 17th edition IEE regulations probably achieved more than most changes to the rules has achieved by making it a law that all new consumer units must be fitted with an RCD or residual current device that controls the power at the distribution point of the electrical supply. In this one change a system whereby electrical power is cut off almost immediately upon a loss of current was enshrined in law. This system meant that it was virtually impossible to get electrocuted by a shortage of current through a person to earth, which was possible prior to the introduction of the new consumer units.
There are many ways of distributing current through the system and basically it is still a case of you pay more to get more. If the electrical supply throughout a house is divided into many sections then each section will have a mini circuit breaker and all of these will pass through the RCD. If one circuit has a fault the RCD will take out all circuits immediately, but the circuits can be restored immediately with the guilty circuit being isolated. If you have fewer circuits then the more of the electrical supply will be affected when power is restored.
It is possible to put an RCD on each circuit but in most cases this is too problematical and not necessary. There is, however, still an argument that we could be like many USA systems as they also have a breaker that trips on an over current situation as well as the RCD. This really is a case of whether you wish a “belt and braces” approach.
The major problem is that whilst all new systems must use a consumer unit, which conforms to 17th Edition Rules, it is not compulsory to replace any existing consumer unit with a conforming unit. The fact that this is not even a requirement for the future is strange and it really is up to the electrical industry to try and provide as much information and advice as possible. This, with luck, would bring quite a lot of systems, which have dangers in the system into a fail safe mode. However this would need legislation if it were made mandatory to replace all older non-conforming units.
Consumer Units, Circuit Protection Devices and Accessories – A Glossary
A consumer unit is the electrical device used to distribute power throughout a domestic dwelling. Acting as a safety device, protecting against injury through electrical shock, a consumer unit houses protection devices which also protect household appliances from overload.
A consumer unit’s first function is the organisation of electrical ‘circuits’, such that the different ways in which we use electricity throughout the home may be safely and more easily managed. A typical domestic installation, for example will have the following circuits: Ring main for power sockets and items like washing machines and TVs, Lighting, smoke alarms, cooker, shower etc.
This is the ‘Double Module’ device which sits on the far right hand side of a consumer. It usually has a big red bar switch and acts to isolate the entire board. This means that by manual operation it can cut power to every circuit in the installation. Main Switches are almost always rated at 100 amp, allowing it to isolate an installation which pulls no more than 100 amps in total across all circuits.
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