The Benin Sustainable and Secure Access to Electrical Energy Project (PADSBEE), initiated by the Government of Benin, aims to develop sustainable access to electricity through the construction of new lines to extend distribution networks. The construction of overhead distribution lines requires perfect knowledge and application of the climatic, electrical and geometric constraints to which they are subject. Our work thus consists in designing a software package for the electrical and mechanical dimensioning of medium-voltage overhead lines, with its application to the 3 km long 20 kV overhead line in the town of Come, in the Mono department. Based on the characteristics of the conductor to be used, the current criteria and the maximum permissible voltage drop, the electrical dimensioning allowed us to determine an Almelec conductor with a cross-section of 75.5 mm2 and composite insulators with a 490 mm creepage distance. From a mechanical point of view, verification of clearances to obstacles led to the selection of reinforced concrete supports 12 m in line and at a standstill, and 13 m at an angle. Wind and conductor loads on the supports led to the selection of Class A supports with a force of 300 daN in alignment, a Class A support with a force of 800 daN at an angle, and Class C supports with a force of 2000 daN at a stop. Reinforcements are of the sheet-vault type in alignment, horizontal stirrup in angle and single cross-member anchorage in stop.