Maximum Current The Wire Can Withstand

The Z large current that the wire can withstand is not calculated, but the experimental results. The test method is to conduct pressure test on a 1m long wire at 20 ° C to obtain the safe current value that the wire can pass continuously. This value will be marked on the nameplate of the product - each brand and model of wire only needs to be tested once.

However, in practice, this current must change, and the factors that will affect the current carrying capacity of the wire in use:

1. Temperature

The higher the temperature, the lower the current carrying capacity of the wire. This is a common problem in Z, and it is also the main reason why the cable used in construction needs to be thicker than the cable used in plug-in row. Moreover, in many cases, the ambient temperature is uncontrollable. Ventilation effect, sunshine and cable density will affect the ambient temperature and then the current carrying capacity of the cable.

2. Cable density

The cable laying is too dense, which will not only produce excessive temperature. When multiple conductors are laid together, proximity effect and skin effect will also be formed, so that the charge will be concentrated in the local section of the conductor and the allowable current carrying capacity of the conductor will be reduced.

3. Length

The longer the cable, the lower the ampacity. The difference between the current carrying capacity of a 100 meter cable and that of a 10000 meter cable is not an order of magnitude. (most of the above external factors affecting the current carrying capacity of wires are power supply and transmission, industrial and commercial power consumption. Due to the small change of ambient temperature and short distance, the impact of external factors on cables can not be considered.)

Internal factors affecting the current carrying capacity of wires:

In addition to some external factors that will reduce the ampacity of the cable in a specific environment, the more important factor that can determine the ampacity of the wire is the internal factor of the wire, which is mainly determined by the following three points:

1. Core area

That is what we often call "wire diameter", such as 2.5 mm2 and 4 mm2, which are common in decoration. However, it is emphasized here that the current carrying capacity is determined not by the cross-sectional area of the whole line, but by the cross-sectional area of the conductor in the line. The thicker the line, the greater the ampacity.

2. Material conductivity

It depends on the conductor material, such as common copper wire and aluminum wire. The conductivity of copper is at least 30% higher than that of aluminum. When necessary, silver thread may appear. In addition to the substance of the material, it also depends on the purity of the material. Taking copper as an example, the conductivity of red copper with high purity Z is much higher than that of second-class brass.

3. Thermal conductivity of insulating layer

In addition to preventing electric shock, the function of insulating layer also has an important function as anti electric shock - flame retardant. The better the thermal conductivity of the insulating layer material, the better the flame retardant performance. Therefore, the quality of insulating materials determines the current carrying capacity of wires from another aspect.