Line traps inserted into a power line to provide a high impedance at power-line-carrier frequencies (30 kHz to 500 kHz) are covered in this standard. The purpose is to isolate the carrier signal from system impedance changes due to faults or switching behind the point of insertion, and to guide the signal in the proper direction. The standard covers line traps in which the main coil is designed as a single-phase, air-cooled inductor of the dry type.