A method is disclosed for monitoring galvanic isolation of a fuel cell device. At least one stack of fuel cells and at least one load circuit for fuel cells are arranged to an electrically freely floating configuration towards at least one structure near fuel cells. A controlled switching is performed via at least two switching points to at least one measurement element having known impedance in connection to the at least one structure. Measurements are performed from the measurement element to form voltage information. The voltage information and at least voltage information between switching points are processed to check floatages of fuel cells in relation to said at least one structure.