A system configured to monitor an operating electrical device includes a testing channel coupled to the device. The device is coupled to an electric power source through at least one electric power transmission channel. The power source is configured to transmit electric power at a first frequency. The testing channel is coupled to the power transmission channel. The system also includes a signal generator coupled to the testing channel. The signal generator is configured to inject testing signals into the testing channel at a second frequency that is greater than the first frequency. The system further includes at least one apparatus magnetically coupled to the power transmission channel. The magnetically coupled apparatus is configured to present a first impedance to the electric power at the first frequency and present a second impedance to the test signals at the second frequency. The second impedance is greater than the first impedance.