A method for preventing fire in electric circuits and arrangements includes measuring an electric current of a controllable section, separating a high frequency component therefrom, amplifying and rectifying a first harmonic signal, determining a spark current value, forming the first harmonic signal from a measured current signal range, measuring short-circuit and/or overload and/or a leak, and/or measuring the electric circuit voltage, in forming a warning and/or switching off signal of the controllable section. The signal amplitudes and/or other parameters including a spark striking-suppression cycle are measured for determining a spark current. The fire preventing device includes a unit for forming a signal of first and higher harmonics, a unit for determining a spark current quantity, a unit for measuring short-circuit and/or overload and/or leak currents, and/or electric circuit voltage measuring currents, units for forming a warning and/or switching off the controllable section signal. The spark current quantity determining unit has devices for measuring signal amplitudes and/or other parameters including a spark striking-suppression cycle.