Why cable rating in max. A, resistance in max. W?
Hello,
Why are max. values for cables in amperes, but for resistors in watts?
Don't cables also heat up due to their resistance? What's different about this compared to wire-wound resistors, where amperes are the deciding factor for cables?
And a completely different question: With potentiometers, the maximum possible power (usually 2W) decreases the further you turn it down, right? If I set a 10KΩ potentiometer to 1KΩ, I'm only using 10% of the winding…
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You could also specify the load capacity of the cable in W/m.
The current carrying capacity is just closer to what you are interested in in the end. IdR you want to know how much power you get safely over the cable, the entire heat loss is usually of secondary importance.
You can’t say that in general. Other factors are also interesting for cables, such as stress resistance, short-term current density, capacitance coating, rated voltage or also rated power! The fact that only the maximum current carrying capacity of cables is not correct.
Resistances are also conductors, however made of materials or Substances which intentionally inhibit the flow of current. Depending on the application, the characteristic values such as voltage strength, maximum power loss or parasitic inductance are also important here.
For rudimentary applications, in both worlds, the characteristic values which are most often of interest are given.
A current flows through the cables, which is specified in ampere. Resistances bruise power, which is now given in Watt.
The specified power value for potentiometer indicates the maximum power, normally you pick up a voltage there, which are not built to get over the tap max. Electricity can flow.
Hello
For wires it is important how many amperes you can send through, which are not hot.
Resistances are hot, so it must be specified how much watt they can carry
Greetings HobbyTfz
Wires are already hot, they must not get too hot and therefore there is this current limit.
How hot a wire may be depends on the surrounding material and the cable insulation. High-temperature lines are designed, for example, up to a surface temperature of up to 90° C. or even partially more. The current upper limit is then the limit so that the cable is not hotter than its permissible surface temperature.
Of course, other limiting factors such as the permissible voltage drop etc. also exist in installation technology, but these are specific to the application.
Wires are only hot when they are overloaded.
It is precisely this that the N need not be stronger than the phases
However, it is possible to give strong unsymetries and harmonics, depending on the connected consumers, whereby more current runs through the neutral conductor because, in contrast to the 50 Hz, these are then added in the neutral conductor instead of mutually canceling, even with symmetrical loading, either filter or more cross-section is required for N.
However, if necessary, all cross sections are increased not only N .
In general, the 3 phases and the neutral conductor are of the same magnitude because the phase shift of the neutral conductors does not load more strongly.
But then you would have to increase all cross-sections accordingly, not only neutral conductors, only it is usually not made – not taken into account as far as I know.
Not always, it depends on what it is.
If the circles are then sorted still nicely by use, some more can come together at the neutral conductor .
The neutral conductor is not loaded to a greater extent at 3 phases than the phases, so the neutral conductor does not need to be stronger.
Do not see industrial plants and mobile devices as an exception. But even in the case of house installations it can be at least warm in exceptional cases, e.g. the feed lines to the individual apartments where they still run together in a cable route. This is not all apartments at the same time and therefore can not drive the full reduction factor for the high occupancy of the route, but if then the nice warm but not as warm as the extra heat-resistant of the industry will be utilized. (Construction phase – everywhere heating fans & spotlights for lighting & construction workers-silver devices…).
Or in the fuse box if after the FI the machines are nicely distributed to the three phases but only one neutral conductor is looped through with the same cross section…
I would rather describe the house installation as a special case or it is also covered by these points:
Bzw
It is important for every application to adhere to the standards.
These are special cases, in house installations, wires cannot get hot
These are special cases, in house installations, wires cannot get hot
It depends of course on what is called hot, but, depending on the application, they can reach significantly more than ambient temperature.
Whether and how hot a cable may be depends on the standard, application and cable specification.
As long as my cable is not overloaded thermally and no standard is violated, it may also reach surface temperature above 60°C, unless otherwise other components are overheated.
In particular, when it comes to weight, it can be quite possible to reduce the cable cross section even if the cable then reaches significantly more than ambient temperature at maximum load. Of course, however, I must move within the framework of the respective standard and if the safety is demonstrated by suitable tests.
Industrial machines – plasma / laser cutter … The movable part should remain dynamic/fast = light …. There the cables are often designed to become hot when the machine is fully loaded, but within the cable specifications.
In mobile devices where weight/size/price is more important than a few watts loss the same way. Then it goes as far as they would burn through in case of continuous stress and they have a fixed maximum ratio of operating time to rest time.
Also some longer charging cables from e-cars are at least good warm so they are not too disturbing / heavy / big.
When a wire gets hot then it is too weak or the fuse too strong. You have to prove that wires are deliberately hot
However, there are also devices and installations where it was deliberately designed to get hot (without external heat source). To save weight. They are therefore not overloaded as long as within the specifications.