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Extensive experience in overseas project submission

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  HomeTechnical Lib Cable size selection

Cable size selection

Generally speaking, cable size selection is based on the three factors: Current carrying capacity, Voltage drop and Short circuit rating.

The current carrying rating is determined by the conductor size, the installation method and thermal heating of the cable. Voltage drop mainly depends on the length of cable being installed. The longer the cable install, the bigger the voltage drop occurs. Short circuit ratings are based on the maximum current withstand capability of the cable in a short circuit condition. The cable should be capable of withstanding this current without thermal damage until the fault condition can be switched to safety through a device like a circuit breaker of fuse.

Short-circuit rating is the maximum short- circuit current the cable can safely withstand when protected by a specific overcurrent protective device or for a specified time. The specific data for the above factors can be find in BS 7671.

Usually, the cross-sectional area of the conductor should be greater than or equal to the standard for the amount of current required to be transmitted, because the larger the cross-sectional area of the conductor, the greater the current that the corresponding cable can withstand, and the less loss generated by it.

When selecting the conductor cross-sectional area, you also need to pay attention to the following points.
1. The cross-sectional area of the cable should be selected reasonably. If it is too small or too large, it will have an adverse effect on power transmission.
2. The overall material and quality of the cable should comply with regulations to ensure the safety of power transmission.
3. The installation length of the cable should be as short as possible, which can reduce the loss that the cable needs to bear.