Abstract— Inspection, maintenance, and repair of electric power transmission line systems is a core function of the electrical engineer, who does such work on a daily basis for electrical power distribution systems in all regions. In Thailand, this task is the responsibility of the Provincial Electricity Authority (PEA). This article proposes a mathematical model of the magnetic field around a 115 kV power transmission line hung over another 22 kV line on which the staffs are performing work. This was modelled using a 3-dimensional finite element model. It is to be used as a diagnostic tool for predicting the magnetic fields around power distribution cables. This study focused on shielding magnetic devices from electricity to reduce the negative effects of magnetic induction on workers maintaining 22 kV transmission lines. The current study reports the results of decreased use of magnetic materials to reduce the magnetic field and the effects of magnetic fields on human beings according to ICNIRP standards.