Abstract: A tamper-proof adaptor is secured to an electric meter or is formed as a part thereof to form a unitary device which, upon first being plugged into a conventional wall pan and thereafter being removed therefrom, automatically restrains reinsertion of the device into the wall pan. The forces necessary to disengage the device from the wall pan are utilized to physically disengage the meter prongs from extension prongs within the adaptor and, thereafter, an insulating bar is disposed blockingly between the extension prongs and the meter prongs to prevent reconnection thereof.