A trial block intended to be implanted in the circuit linking a device to be tested such as a counter or a protective relay and a power source supplying the device to be tested such as an intensity sensor and/or a voltage sensor, the trial block comprising: - a base including a plurality of internal electrical circuits able to allow the transmission of information from the power source to the device to be tested, - a protective cover intended to be assembled with the base in a removable manner to form a closed enclosure in which the internal electrical circuits are housed, - the base and the protective cover being configured so that the removal of the protective cover gives access to a reception location delimited by the base and able to receive by plugging a test plug independent of the trial block and electrically connected to a test equipment, in particular a voltmeter and/or an ammeter and/or a dummy current source, the base and the protective cover comprising electrically conductive elements connected together and configured so as to ensure continuity, the trial block being characterized in that said elements are further configured so as to ensure magnetic shielding closure such that the enclosure delimited by the base and the protective cover is a Faraday cage protecting the internal electrical circuits from the magnetic fields outside the enclosure delimited by the base and the protective cover, in that the base comprises at least one input socket of the multi-contact type accessible from outside the enclosure and whose contacts are respectively electrically connected to the internal electrical circuits so that the input socket is connected to all the internal electrical circuits at the same time, the input socket being configured so as to be able to be connected to a first connector of the multi-contact type independent of the trial block and whose contacts are electrically connected to the power source, in particular via a multi-conductor cable, in that the base comprises at least one output socket of the multi-contact type accessible from outside the enclosure and whose contacts are respectively electrically connected to the internal electrical circuits in a manner that the output socket is connected to all the internal electrical circuits at the same time, the output socket being configured so that it can be connected to a second connector of the multi-contact type independent of the trial block and whose contacts are electrically connected to the device to be tested, in particular via a multi-conductor cable, in that the base comprises a removable hood whose removal relative to the rest of the base gives access to the internal electrical circuits and whose nature and/or shape is adapted to the nature of the input and output sockets and in that the removable hood comprises part of the electrically conductive elements constituting the Faraday cage. - a base including a plurality of internal electrical circuits able to allow the transmission of information from the power source to the device to be tested, - a protective cover intended to be assembled with the base in a removable manner to form a closed enclosure in which the internal electrical circuits are housed, - the base and the protective cover being configured so that the removal of the protective cover gives access to a reception location delimited by the base and able to receive by plugging a test plug independent of the trial block and electrically connected to a test equipment, in particular a voltmeter and/or an ammeter and/or a dummy current source, the base and the protective cover comprising electrically conductive elements connected together and configured so as to ensure continuity, the trial block being characterized in that said elements are further configured so as to ensure magnetic shielding closure such that the enclosure delimited by the base and the protective cover is a Faraday cage protecting the internal electrical circuits from the magnetic fields outside the enclosure delimited by the base and the protective cover, in that the base comprises at least one input socket of the multi-contact type accessible from outside the enclosure and whose contacts are respectively electrically connected to the internal electrical circuits so that the input socket is connected to all the internal electrical circuits at the same time, the input socket being configured so as to be able to be connected to a first connector of the multi-contact type independent of the trial block and whose contacts are electrically connected to the power source, in particular via a multi-conductor cable, in that the base comprises at least one output socket of the multi-contact type accessible from outside the enclosure and whose contacts are respectively electrically connected to the internal electrical circuits in a manner that the output socket is connected to all the internal electrical circuits at the same time, the output socket being configured so that it can be connected to a second connector of the multi-contact type independent of the trial block and whose contacts are electrically connected to the device to be tested, in particular via a multi-conductor cable, in that the base comprises a removable hood whose removal relative to the rest of the base gives access to the internal electrical circuits and whose nature and/or shape is adapted to the nature of the input and output sockets and in that the removable hood comprises part of the electrically conductive elements constituting the Faraday cage.