Expert: when selecting and installing cables the use conditions must be known
Considering the rapid development of the construction market, the cable manufacturer Prysmian Group reminds that when buying a cable, it is very important to choose the right cable type and adhere to the installation requirements. Failure to do so may result in significant material damage.
According to Prysmian Group experts, when choosing a cable, one must first understand what the cable is needed for and what one wants to achieve by making a cable connection. Next the environment in which the cable will be located must be assessed. “The installation conditions of the cable also directly affect how much current can flow through it. It should also be noted that although the cables appear to be very similar, due to their construction and the materials used, there may be restrictions on the cable environment,” said Andero Hännikainen, long-term Sales Manager at Prysmian Group. “For example, some black cables can be installed directly in the soil, while others must be protected with a pipe when installed in the soil.”
Important parameters
According to Hännikainen, one of the most important parameters of an electric cable is the cross-section of its conductor. Although the cross-section is given numerically in square millimeters, actually the size of the cross-section is only indicative and the electrical resistance of the cable is important. “Therefore, there may be times when measuring the physical cross-section of the core gives a different result than the one marked on the cable. The resistance limits of the core are given very precisely, as the amount of current the cable can carry depends directly on it. Like an electric heater, a cable heats up due to the current flowing through it. The difference is that the resistance of a 1.5 mm² cable of one meter is about 4,000 times lower than that of a 1kW heater, and thus the heating at a similar current is significantly less,” said the sales manager.
The maximum operating temperature of a cable is usually limited by the properties of the materials used in the cable, beyond which they begin to lose their properties. The specified temperature should not be exceeded either by external factors such as solar heat and hot surfaces and the heat generated by the load current, or by a combination of these.
“Therefore, the warmer the area around the cable, the less current-carrying capacity it has and vice versa - well-cooled cables can have much bigger current-carrying capacity. For example, the difference in the maximum load current of a cable installed in wet soil compared to that installed in dry sand can be almost double,” explained Hännikainen. “There is also a direct loss of heat that cannot be usefully consumed and it may happen that significant savings can be achieved by using a larger cross-section. All these factors must be taken into account in order to find a suitable cross-section.“
Better choices
In addition to the current-carrying capacity of the cable, there are strict requirements for cables to be installed in buildings set in the Construction Products Regulation (CPR), key legislation for fire safety. Prysmian Group has developed CableApp to help you make energy-conscious decisions when choosing cables. Hännikainen said that the application takes into account a number of different factors and, in addition to the minimum technical solution, also conveniently shows how much money and CO2 emissions can be saved by using a cable with larger cross-section. “Larger resellers have also been added to the app to make it easy to find the nearest place to buy cables,” he added.
The app is available on the web at www.cableapp.com or can be downloaded to your mobile device from Google Play or App Store.
According to Hännikainen, customers often mistakenly believe that a fire-resistant cable can be installed in very hot places. “This is not true, as these cables also have a maximum operating temperature, which is generally similar to conventional cables. The purpose of fire-resistant cables is to ensure the operation of the electrical circuit in the event of a fire for a certain period of time,” he explained. He added that fire resistance is achieved with different materials and structures, and all the plastics in the cable may burn in the event of a fire. In the case of a fire-resistant cable, the corresponding fastening accessories must also be used – even ordinary metal cable ladders may not be able to withstand the current-carrying capacity of the cables in the event of a fire, not to mention plastic cable ties.
“There is no use of a high-quality cable if the systems that support it do not enable it to perform the given task,” said Hännikainen. “We have also seen cases where the cables on the roof of the house are tied to the lightning protection system. Such an installation is very dangerous, because in the event of a lightning strike, the entire electrical system of the building is likely to be destroyed and there is a real risk that also the building will catch fire.”
The right work practices are important
As a general rule, cables are not designed to withstand impacts, so stepping on the cables and standing on the cable reels should be avoided. Care must also be taken when fastening bushings and cable clamps – fastenings must be made in accordance with the instructions, not with maximum strength, or to the end of the thread.
“As winter is coming, attention must be paid to the cold resistance of the cable. Namely, the temperature at which the cable should be handled applies not only to installation but also transport. It takes only a few hours of severe frost that the plastics used in the cable may become very brittle. If, for example, a cable reel that has been left in the frost is carelessly thrown into the trunk of a car, or even a not very heavy object accidentally falls on the cable, the result may be that although the damage can be relatively difficult to see, the cable is damaged,” warned Hännikainen. “Often we cannot be sure if a cable has been handled gently in a third party's warehouse or when transporting the product in cold conditions, so we have to be careful in case of heavy frost. To simplify installation and minimise risks, it is recommended that the cable be warmed up before use.”
Hännikainen added that attention should also be paid to cables, which may not be manufactured in Northern Europe. This is because in Central and Southern Europe, different materials are often used that are less resistant to cold. According to him, the installation temperature of cables from Prysmian Group is -15 C°, while in case of many manufacturers from other regions it can be -5 C° or even +5 C°.
For the best results, always follow the cable manufacturers’ product sheets during installation and pay attention to which cable is installed, where, and how.
The article (in Estonian) was published on the site Ehitusuudised.ee.