The invention relates to a method for operating a public address system with a control center to which loudspeakers are connected via a two-wire loop system that is routed via isolator modules. A fault can be located on the loop system if the control center measures the impedance of the loop system successively from isolator module to isolator module and the impedance of the entire loop system, inputs the measured values as target values into an impedance table, periodically measures the impedance of the entire loop system during operation, compares said impedance with the corresponding target value from the impedance table, generates a fault message upon determining a deviation, ascertains the fault location by comparing the measured value with the individual target values in the impedance table, and displays said fault location.