To achieve a perfect match between power cables and protective circuit breakers, the right selection of these two products is very important. There are few factors need to be considered such as cable size , laying method, line voltage drop, thermal stability, and environmental conditions etc, this can be a final coordination between power cables & circuit breakers.
- Ambient temperature
Under different laying conditions, the ambient temperature used to determine the cable current carrying capacity varies. When the ambient temperature at the laying location is different from the reference temperature, the cable current carrying capacity should be corrected according to the following formula (equation omitted), where Kt – correction coefficient; θ N – Long term allowable working temperature of cable core (° C); θ A – Environmental temperature at the cable laying location (° C); θ C-The basic data of the cable corresponds to the reference temperature (° C);
2. Cable Installation method
There are various laying methods for cables, such as direct burial, threading through pipes, cable trenches, cable trays, cable tunnels, etc. Under different laying methods, the allowable continuous current carrying capacity of cables has different correction factors. The cable design specifications provide a correction coefficient table for the allowable current carrying capacity of cables under different laying conditions. During the design process, corresponding correction factors should be selected based on the specific situation of the project.
3. Environmental conditions
The environmental conditions for cable laying include normal environment, disaster hazardous environment, explosion hazardous environment, etc. Under different environmental conditions, the current carrying capacity of the cable should also be multiplied by the corresponding correction factor. After determining the influencing factors of cable current carrying capacity, the selection of distribution cable cross-section cannot be directly determined based on the current carrying capacity. There are other influencing factors for the selection of distribution cable cross-section. In design, the cable cross-section should be mainly verified based on the following points:
1. Temperature rise;
2. Line voltage drop;
3. Economic current density;
4. Thermal stability;
5. In specific designs such as mechanical strength, the calculation method of cable cross-section should be selected based on actual conditions. For example, long cable distribution circuits should consider the impact of line voltage drop; For circuits where low-voltage electrical switchboard directly distribute power to low-power equipment or lighting boxes in the distribution room, it is necessary to conduct thermal stability checks on the cable cross-section. In addition, for circuits with severe harmonics in the power supply and distribution system, the influence of the size of harmonics on the cable cross-section should also be considered.
If still any questions, please conact us at : info@powertel-solutions.com ; our expert engineers will help you to select a right cable size to match a circuit breaker, assuring the safety and stability of your power distribution system.