Testing of low-voltage electrical installations is carried out in order to determine the safety and resistance of the electrical installation according to the external influences acting on the installation from the environment that surrounds it during the entire lifetime of exploitation and safety of users who use electricity that is distributed through low-voltage electrical installations. It is mandatory to assess the safety of the electrical installation in terms of mechanical durability, resistivity and protection against thermal effects due to overload and short circuits, insulation integrity, basic protection against contact of live components in normal operation, and availability for inspection and maintenance. From the aspect of user safety, it is necessary to determine the form of protection against inadvertent contact with live components in the event of a malfunction. To establish suitable protection for the users of the electrical installation against unintended voltage exposure of touching live parts in the event of a malfunction, it is necessary to understand effects of the electric current on the human body in the moment as the current passes through it. The human body represents an impedance that decreases as the touch voltage increases. It is possible to reduce the impedance of the human body by increasing the transient impedance between live parts that can be touched by a human in the event of a fault. This is achieved by an adequate selection of electrical appliances that use safe low voltage for power supply in the SELV, PELV, and FELV protection class and by choosing appliances enclosed with double or reinforced insulation. Another type of protection is the automatic power cut off in the event of a fault before the appearance of a high contact voltage that is dangerous for the human body. This is achieved by the correct execution of the electrical installation in the TN, TT, and IT grounding systems in combination with the correct selection and installation of equipment for automatic power cut-off. Electrical installations in which the power supply must not be switched off in the event of a fault are carried out in the IT grounding system with insulation’s control elements. The objective of such implementation is to minimize the fault loop impedance to the lowest possible value, so the current that could potentially pass through a human body in case of a fault, to be of an intensity that poses no danger to the human body. TN and TT earthing systems in conjunction with automatic cut off mechanisms operate using the reverse logic of IT earthing systems. The goal is to reduce the impedance of the fault loop so that the automatic power disconnect devices will selectively shut down the faulted circuits in time before the contact voltage rises to a value that can cause current to flow through the human body of a magnitude dangerous to the human body.