The best technologies are often those that remain unseen because they behave exactly as the user intuitively expects, all the time and every time. One of the masterpieces of engineering is the transformation of the potentially dangerous quantity we call electricity into a completely safe everyday commodity.
Most people are aware that touching a live wire carrying 220 V can be a painful experience. But despite the ubiquity of such wires in their homes, a very high level of protection is provided. A sophisticated system ensures the safety of people, of the installation itself and of the entire building. The elegance and the significance of such installations are commonly hidden away in basements and broom closets, and behind plaster. This article attempts to give the reader a peek behind the scenes for an impression of the hidden technology that contributes to everyday wellbeing.
Bringing Technology Home
From time to time most people have had to go to the basement in order to fix a fuse, probably unaware of the purpose of all the various elements of the fuse and metering panels. There is a broad range of different building blocks that can be installed in a house. ABB, as one of the leading producers of devices and components for domestic and commercial applications, offers nearly all necessary units.
Prevention of excessive currents
One of the most important and widely used units in the field of home and building protection is the miniature circuit breaker (MCB). MCBs are used for so-called line and fire protection, ie, they protect buildings and appliances from the effects of short circuits and overloads.
An MCB is also responsible for the protection of the connected lines themselves: The unit must be designed for the expected load of all connected devices. If there are too many devices or if they have too high a consumption, a permanent overload can ensue. Such an overload may be insufficient to qualify as a short circuit, but can nevertheless cause the line to heat up, possibly resulting in a fire. Overloads of longer duration are detected by a thermal element inside the MCB that opens the circuit to prevent damage.
A broad and distributed use of MCBs increases what is called selectivity of protection. If a washing machine, for example, is protected by an individual MCB, a malfunction of the machine will lead to its disconnection. The supply of other devices, however, will remain unaffected, permitting them to continue operating. The more MCBs are installed for individual applications, the smaller the effects of any individual incident.
Another advantage of MCBs is their reusability. Traditional fuses must be replaced after each operation, which not only means that every household must keep a stock of spare fuses, but also introduces a certain risk of the incorrect types being used. MCBs don’t have to be removed or replaced: A layperson can easily close the affected circuit by operating the toggle of the released MCB (of course after having addressed the problem, eg, by unplugging the defective appliance).
Well protected
Residual current devices (RCDs) represent another indispensable type of protection device. In accordance with international and national standards in all EU countries, all socket outlets and mobile equipment for outdoors must be protected by RCDs. RCDs detect leakage currents, which leave an electrical line and drain to the ground even if the current is very small. Like an MCB, it also has a detection mechanism for currents. When the leakage current rises above a certain thresh-old, the RCD immediately interrupts the current.
RCDs generally provide 3 kinds of protection:
- Basic protection. Normally this protects people from electric shocks. It can be the insulation of a cable or the housing of an electrically operated device or piece of equipment. If the basic protection is defective and someone touches the faulty part or if people deal carelessly with electricity, the RCD trips and interrupts the concerned circuit. In this case the RCD provides additional protection against electric shocks.
- Fault protection. This protects the user if a high voltage occurs on the housing of the device. The RCD will switch off the concerned electrical circuit, preventing a person from touching the faulty device.
- Preventative fire protection. This is needed if leakage current of an electrical line drains to the ground for some time. In this instance, an MCB would not switch off because the current is too low, even though this fault current might cause a fire. Instead, the RCD switches of the concerned circuit.
The importance of selectivity applies here as well. A single RCD should not protect all sockets or all light circuits in a building, as all lights would go out in the event of a failure.
Comfortable safety
The best technologies are often those that remain unseen because they behave exactly as the user intuitively expects, all the time and every time. ABB technology does precisely this. Whether people are watching a football match under floodlights, or shopping in a brightly-lit mall in an air-conditioned atmosphere, ABB technology is providing safe and reliable electrical operation of building and residential infrastructure.
