DEFECTIVE EARTH TESTING FOR AN ELECTRIC FENCE ENERGIZER

In an electric fence energizer there is an exterior earth connection such as an earth connection post (16). The electric fence energizer comprises in the conventional way a transformer (T) having a primary winding (L.sub.1) and a secondary winding (L.sub.2), one exterior terminal (9) of which is connected to the conductor (17) in the electric fence and the other exterior terminal (11) is connected to the earth connection, high voltage pulses being induced over the secondary winding (L.sub.2) when voltage pulses are applied over the primary winding (L.sub.1). For a determination of the quality of the earth connection, the voltage over a small part of the secondary winding (L.sub.2) is obtained capacitively by means of an extra winding (L.sub.3) in the transformer (T). For an evaluation of this voltage, it is connected, only for a determined polarity, to a charging circuit for a capacitor (C.sub.2), which is discharged over a known resistor (R.sub.2, R.sub.3). The voltage (V.sub.21) over this capacitor (C.sub.2) is processed for a determination of the quality of the connection to earth. Then the time difference can be determined between the time (t.sub.0) when the induction high voltage pulse over the secondary winding (L.sub.2) starts, and the times (t.sub.1, t.sub.2) when a voltage change of the capacitively obtained signal after that starts and when the voltage returns to its stationary value. These time differences are compared to threshold values for determination of the quality of the connection to earth. The capacitively obtained voltage can also be used for other determinations in the electric fence energizer.