Will the current carrying capacity of cables be reduced when a large number of cables are laid in groups?
For cables laid in underground pipelines, when using the load factor, the heat capacity of the average heat loss of the pipe group and the surrounding soil shall be considered.
When a large number of cables are laid in groups, due to mutual heating, the current carrying capacity of cables is reduced. Sometimes two or more parallel cables with smaller specifications are considered to replace cables with larger specifications, because the current carrying capacity of large cross-section cables will be reduced due to skin effect and proximity effect. On the other hand, the reduction of the ratio of the surface area to the cross-sectional area of the large cross-section cable makes the heat dissipation capacity of the large cable poor. If multiple cables are used in parallel, the relative position of each cable shall be considered to reduce the uneven distribution effect of cable current carrying capacity.
For cables laid in underground pipelines, when using the load factor, the heat capacity of the average heat loss of the pipe group and the surrounding soil shall be considered. The temperature of the underground part varies with the change of the average heat loss, so it is allowed that the higher short-term load coefficient is the ratio of the average load to the peak load, which is usually measured based on the average day and night load. The peak load generally refers to the average value of the maximum load occurring within 24h and 0.5~1h. For directly buried cables, the average surface temperature can be limited to 0~60 ℃ according to soil conditions to prevent soil moisture loss and cable thermal breakdown.
When the cable is close to other loaded cables or heat sources, or when the ambient temperature exceeds the ambient temperature of the specified cable ampacity, the rated ampacity of the cable must be reduced. The normal ambient temperature of the cable device refers to the temperature at the place where the cable is installed when the cable is not loaded. In order to properly determine the cable specifications required for a given load, this temperature should be thoroughly understood. For example, the ambient temperature of a cable laid separately from other cables in the air refers to the temperature before the cable is loaded. For cables in the air, it is also assumed that there is enough space around the cable to distribute the heat generated by the cable, and the temperature of the whole room will not be increased. If the above correct conditions are specified, the following environmental conditions can be used to calculate the current carrying capacity of the cable.