A method of securely registering a removable electrical apparatus (4A, 4B, 4C) when it is installed in an electrical system as a replacement for a failed removable electrical apparatus, characterised in that the method comprises the steps of: - detecting a failure of a removable electrical apparatus (4A, 4B, 4C) installed within an electrical system associated with an electrical installation, the electrical apparatus being an electrical protection and switching apparatus, or a contactor, or an apparatus for measuring one or more electrical quantities, or an apparatus for monitoring the operation of the electrical installation; then, only if a removable electrical apparatus (4A, 4B, 4C) installed within the electrical system has been detected as having failed: a) following the installation of a new removable electrical apparatus (4A, 4B, 4C) within an electrical system to replace the failed removable electrical apparatus of this electrical system, automatically acquiring, by means of an electronic control module of the electrical system, a first security certificate of the new removable electrical apparatus stored in a computer memory of an on-board electronic computer of the new removable electrical apparatus (4A, 4B, 4C), this first certificate being signed by an authority known to the system; e) verifying from identification information contained in the first acquired safety certificate that the new removable electrical apparatus (4A, 4B, 4C) is of the same type as the failed apparatus that has been replaced, the registration of the new removable electrical apparatus (4A, 4B, 4C) being denied if this new removable electrical apparatus (4A, 4B, 4C) is not identified as corresponding to the failed removable electrical apparatus which it replaces within the electrical system; b) verifying the authenticity of the first acquired security certificate, this verification being performed by the electronic control module; c) generating a second security certificate for the new removable electrical apparatus (4A, 4B, 4C), this second security certificate comprising a key generated by the electronic computer of the new removable electrical apparatus (4A, 4B, 4C); d) obtaining a signature of the second security certificate from a trusted certification authority, the new removable electrical apparatus (4A, 4B, 4C) then being registered within the electrical system only if that signature is obtained; f) revoking the certificate of the electrical apparatus that has been replaced with the certification authority, once the new removable electrical apparatus (4A, 4B, 4C) is registered within the electrical system after step d); and in that the step of detecting a failure comprises detecting a loss of communication link between the on-board computer of the removable electrical apparatus (4A, 4B, 4C) and the control module of the electrical system. - detecting a failure of a removable electrical apparatus (4A, 4B, 4C) installed within an electrical system associated with an electrical installation, the electrical apparatus being an electrical protection and switching apparatus, or a contactor, or an apparatus for measuring one or more electrical quantities, or an apparatus for monitoring the operation of the electrical installation; a) following the installation of a new removable electrical apparatus (4A, 4B, 4C) within an electrical system to replace the failed removable electrical apparatus of this electrical system, automatically acquiring, by means of an electronic control module of the electrical system, a first security certificate of the new removable electrical apparatus stored in a computer memory of an on-board electronic computer of the new removable electrical apparatus (4A, 4B, 4C), this first certificate being signed by an authority known to the system; e) verifying from identification information contained in the first acquired safety certificate that the new removable electrical apparatus (4A, 4B, 4C) is of the same type as the failed apparatus that has been replaced, the registration of the new removable electrical apparatus (4A, 4B, 4C) being denied if this new removable electrical apparatus (4A, 4B, 4C) is not identified as corresponding to the failed removable electrical apparatus which it replaces within the electrical system; b) verifying the authenticity of the first acquired security certificate, this verification being performed by the electronic control module; c) generating a second security certificate for the new removable electrical apparatus (4A, 4B, 4C), this second security certificate comprising a key generated by the electronic computer of the new removable electrical apparatus (4A, 4B, 4C); d) obtaining a signature of the second security certificate from a trusted certification authority, the new removable electrical apparatus (4A, 4B, 4C) then being registered within the electrical system only if that signature is obtained; f) revoking the certificate of the electrical apparatus that has been replaced with the certification authority, once the new removable electrical apparatus (4A, 4B, 4C) is registered within the electrical system after step d); and in that the step of detecting a failure comprises detecting a loss of communication link between the on-board computer of the removable electrical apparatus (4A, 4B, 4C) and the control module of the electrical system.