| 摘要 |
An earthed electrical mains has an earth conductor and two phase conductors, with electrically driven appts. connected via leads to the earth conductor, and via connectors to the mains. Between the appts. is connected a lead comprising a conductor and an O-conductor. The appts. may be respectively a mixer board and an amplifier. In one of, or in both connectors or in either or both appts. is a circuit which automatically assumes one of two conditions, viz. under normal operation an insulating state with high inner impedance or resistance, and under conditions where voltage or current in the closed earth lead is dangerous for persons or property, a conducting state with low inner impedance or resistance. In its insulating state, the circuit may have an impedance pref. higher than 100 ohms, whilst in the conductive condition the impedance is 0.01 ohms. or less. |
