When a large number of cables are laid in groups, their current-carrying capacity can be reduced due to their mutual heating. Sometimes, cables of big sizes are considered to be replaced by two or smaller parallel ones because the current-carrying capacity in each unit of a section shall be reduced owing to the skin effect and proximity effect of big section cables. On the other hand, the diminution of the ratio between surface area and cross-sectional area of big ones may lead to their weakness in heat dissipation. The relative position shall be paid special attention to on the condition that many cables are paralleled so as to bring down the nonuniform distribution effect of their current-carrying capacity. For those laid in underground pipelines, the average thermogenesis of heat capacity of pipe group and soils around it should be considered while using the loading factor. Underground temperature varies with the change of average thermogenesis. That means it is permissible that the upper short time load factor is the ratio of average load and top-load and is usually measured based on mean load round the clock. Top-load usually refers to the average value of maximum load emerging between 0.5 and 1 hour in 24 hours.

As for the buried cable, its average surfacial temperature can be restricted between 0℃ and 60℃ according to soil conditions in case of loss of soil moisture and thermal breakdown. Cables’ rated current-carrying capacity must be lowered when the following conditions exist:
1, Cables are close to on-load ones or heat sources.
2, Ambient temperature surpasses what’s been restricted in current-carrying capacity.
The cable unit’s normal ambient temperature refers to the temperature of the location where cables are fixed without load. Understanding this special temperature thoroughly is a necessity to confirm the cable specification of a fixed charge properly. For example, the ambient temperature of cables laid separated from other ones in the air refers to the temperature before it’s on-load. For cables in the air, it’s presumed that there is enough space for them to dissipate heat and shouldn’t heat the house up. If the above correct conditions are stipulated, the under-mentioned environment condition can be used to calculate the current-carrying capacity of cables.