Recently, micro unmanned aerial vehicles (MUAVs), particularly multicopters, are expected to be used for rescue missions and investigations all over the world. However, their operating time for conducting actual missions is currently quite short, typically 20 minutes or less. To extend the flight time, and to prevent the multicopter from leaving the flight area caused by incorrect operations, it is proposed to use an electrical cable as a tether to supply electric power for to the multicopter. To realize such a system, the cable selection is critical. Therefore, in this research, we model the electrical devices (motors and ESCs) on the multicopter, and discuss the optimal cable selection. In this paper, we propose our cable selection method, and introduce our power-feeding tether system that can be carried by unmanned ground vehicles.