Patent attributes
A protection apparatus (48) is provided which in addition to protecting electronic equipment (5) from overvoltage transients is also able to provide an indication of whether or not said transients are due to impedances associated with poor earthing. In one embodiment the protection apparatus (48) includes an input terminal (42), an output terminal (60) and a ground reference terminal (62) with a transient blocking unit (50) arranged to isolate the output terminal (60) in response to the destructive transient voltages. A gas discharge tube (46) is provided to conduct transient currents associated with the destructive transient voltages to the earth reference connection point (62); and an indicator (58), such as a fuse or circuit breaker is placed in series with the transient blocking unit (50) to indicate the presence of a voltage resulting from an interaction of the transient currents with an earthing impedance.
