RSE has recently developed a fiber optic multi-sensors prototype for an early detection of pre-discharges in, since the appearance of these phenomena, on long term, can give rise to breakdown and consequently can lead to out-of-service. A relevant aspect that would improve the functionality of this prototype in practical applications is its automated temporization. Until now, this temporization was performed by mean of a trigger board externally connected to a measure transformer (TV) in order to synchronize signals acquisitions with the phase of the voltage applied to the MV switchboards. This connection could limit the application of this system in a real MV substation; actually this connection could not be always available. In order to overcome this limitation, in this work it was proposed and investigated the feasibility of a fibre optic “trigger” sensor to be integrated into the developed prototype. The proposed solution is based on the use of a transparent low-cost electro-optic ceramics, which behaves as an optical attenuator on a crossing light beam, when an external voltage is applied to its lateral sides. Further components used for the sensor layout are: a 1550nm laser source and an IR photodiode; all these elements are standard fibre pigtailed telecom components to guarantee a low cost assembling. The good performances of the sensor under AC and DC voltage, applied by means of a Voltage Calibrator, were successfully confirmed in laboratory.