Certain types of radio antennas (or their feedlines) require a connection to ground. Since the radio frequencies of the current in radio antennas are far higher than the 50/60 Hz frequency of the power line, radio grounding systems use different principles from AC power grounding. The "third wire" safety grounds in AC utility building wiring were not designed for and cannot be used for this purpose. The long utility ground wires have high impedance at certain frequencies. In the case of a transmitter, the RF current flowing through the ground wires can radiate radio frequency interference and induce hazardous voltages on grounded metal parts of other appliances, so separate ground systems are used.