2023 Author: Philip Bishop | [email protected]. Last modified: 2023-05-24 22:24
- Rated service life
- Warranty service life
- More about guarantees
- Actual service life
- Aluminum or copper?
When laying new wiring, the owner of the premises seeks to do everything so that he does not return to this operation, therefore, when carrying out repairs or during the construction process, he is always interested in how long the service life of the wire is. At the same time, confusion often arises in the definition of the very concept of service life - designers, cable manufacturers and electricians operate with different numbers. Therefore, to begin with, let's define the terminology.
Rated service life
This indicator is of a theoretical nature, it is used by designers when developing a project. Indicates the time interval during which the cables, subject to the rules of their operation, will regularly ensure the delivery of electricity to end consumers. Example: for NYM cable operating in the temperature range from -50 to +50 ° С, voltage load for which does not exceed 660 volts, this period is 25-30 years.
The practical meaning of using this concept is only in planning for preventive maintenance and checks on the condition of the wiring. Its actual service life may differ significantly from the nominal one.
Warranty service life
As a rule, the service life of wires and cables guaranteed by the manufacturer is less than the nominal one. For example, in the case of the aforementioned NYM cable, the designer puts in the documentation a nominal service life of 25-30 years, while the manufacturer gives a guarantee for only 5 years. This means that if a breakdown occurs in the cable (or if it melts), which has served less than this time, the manufacturer will replace it free of charge.
But there is one important point. Free replacement is carried out only if a number of conditions are met:
- the seller has ensured compliance with the storage conditions described by the manufacturer;
- during transportation, the rules for its conduct, also described by the supplier, were not violated;
- the installation was carried out by an organization or an individual who has an appropriate license;
- actual operating conditions did not go beyond the values indicated by the manufacturer.
If the cable has been overheated, if a voltage higher than the rated voltage has been applied to it, or the maximum amperage has been exceeded, the warranty will be void.
More about guarantees
Cable manufacturers test their products on dedicated test benches. The checks are carried out in conditions close to real operating conditions. Cables are laid in grooves, in corrugations, terminal connections and twists are included in the wiring diagram. After that, the wiring undergoes "strength tests" - average calculated loads, peak (both in voltage and current) are applied to the wires, the reaction to changes in temperature conditions is checked.
To determine the service life of a PVA wire, the sheath of which consists of soft vinyl, the humidity mode is also changed in the test room, in some cases the wire is checked for its ability to withstand UV radiation.
Checks are carried out at the launch of each new series, when new equipment is introduced, when any changes are made to the technological process. Cables from different lots from different workshops are selectively checked. Changes in the physical characteristics of the cable, its electrical conductivity and resistance are monitored. The integrity of the braid is checked - whether it has begun to lose elasticity or collapse. By changing the test loads and carrying out constant measurement of the characteristics of the cable, it is possible to predict its condition after 10, 20, 50 years of operation in various conditions.
Actual service life
It is this indicator that is most interesting to the owner of the premises. At the same time, in practice, it is here that the largest discrepancy is observed, since the actual service life of electrical wires depends on the mass of factors that were listed just above. If the wiring is carried out correctly, the installation was carried out in compliance with all the requirements of the electrical SNiP, the load power does not exceed the calculated one, and so on, then the wiring can last a hundred years. But if at least one of the many conditions is not met, the service life is shortened.
Much depends on the correct choice of circuit breakers. For example, a solid core with a cross section of 2.5 mm will withstand a current of up to 25 amperes. A 16 amp machine will knock out before such a wire has time to heat up from an increased load. The 40 amp machine will continue to work, and the cable will simply melt when 32-35 amperes flows through it.
Another example: the cable powers a three-way socket in the kitchen, which is connected to a microwave oven, coffee maker, and electric kettle. Under normal conditions, these devices almost never work at the same time. But all of them can be included, albeit for a short time, when preparing or holding a large family celebration. Even short-term peak loads will shorten the life of the wiring.
Overheating is a separate topic. It can be caused not only by excess load, but also by external factors. For example, after laying the cable lines, a fireplace was installed in the apartment and, as a result, some wire ended up in the immediate vicinity of the chimney. Constant heating in the worst case will lead to damage to the braid (and, of course, to a short circuit), at best - to a change in the physical characteristics of the cable, which will reduce its service life.
Aluminum or copper?
This is one of the first questions raised when replacing wiring as part of a home renovation. In general, the answer to it is most often unambiguous - copper. There are enough reasons for this - copper has a lower specific resistance, higher electrical conductivity, almost twice the maximum power load with the same cross-sectional area. And the service life of copper wires is longer - 20-25 years (nominal) versus 15-20 for aluminum. But there are some nuances.
If you change something, then everything is completely. First, the connection of copper and aluminum conductors is a weak point in the wiring even when using a terminal made of a third metal (direct twisting in this case is generally unacceptable, since copper and aluminum form a galvanic pair). Secondly, partial replacement in order to increase the power of the wiring in some loaded area (for example, in a kitchen with a full set of household appliances) will not work. A copper cable laid in the walls directly in the kitchen will indeed cope with the increased load on its own, but the aluminum cable going from the apartment panel to the junction box will not.
Another point that deserves attention is the economic feasibility of such a replacement. The copper core is still more expensive than the aluminum one, and if the house is not "packed" enough for the wiring to really require reinforcement, it makes no sense to change it just because "aluminum is out of fashion."
As for the duration of operation, there are houses in which the actual service life of aluminum wires is already 50-70 years, and the wiring in them does not need to be replaced. As already mentioned, it all depends on the specific conditions.
So, if the house is not crammed with household appliances, and the repair budget is limited, then you can change (if there is such a need at all) for an aluminum one. The only caveat - in this case, it will be necessary to carry out a kind of prevention every two or three years. Its essence is to tighten the clamping screws in switches and sockets. Aluminum is plastic, the force from the screw (or the contact pad pressed by it) leads to its deformation, contact weakens over time, namely, poor contact is the most common cause of fires due to electrical wiring.