An electrical system, comprising: a reefer receptacle (375; 675) having a diagnostic device (370; 670) configured to generate test signals, wherein the diagnostic device (370; 670) is disposed within a housing of the reefer receptacle (375; 675); a reefer container having a monitoring device and an electrical load , the reefer container being portable relative to the diagnostic device (370; 670) and the electrical load comprising a refrigeration unit ; at least one energy transfer link coupling the diagnostic device (370; 670) and the reefer container , the at least one energy transfer link including an electrical connector configured to detachably couple to the reefer receptacle (375; 675); wherein the monitoring device is coupled to the at least one energy transfer link , wherein the monitoring device is disposed between the diagnostic device (370; 670) and the electrical load , wherein the monitoring device is configured to receive the test signals from the diagnostic device (370; 670), and wherein the monitoring device is configured to execute, in response to receiving the test signals, a test procedure on the electrical load while the electrical load is idle or while the electrical load is in service at the respective time, the monitoring device further configured to include into a reply signal results of the test procedure on the electrical load that includes at least one of an identification of the electrical load and details of the test procedure executed on the electrical load ; wherein the diagnostic device (370; 670) is configured to receive the reply signal from the monitoring device . a reefer receptacle (375; 675) having a diagnostic device (370; 670) configured to generate test signals, wherein the diagnostic device (370; 670) is disposed within a housing of the reefer receptacle (375; 675); a reefer container having a monitoring device and an electrical load , the reefer container being portable relative to the diagnostic device (370; 670) and the electrical load comprising a refrigeration unit ; at least one energy transfer link coupling the diagnostic device (370; 670) and the reefer container , the at least one energy transfer link including an electrical connector configured to detachably couple to the reefer receptacle (375; 675); wherein the monitoring device is coupled to the at least one energy transfer link , wherein the monitoring device is disposed between the diagnostic device (370; 670) and the electrical load , wherein the monitoring device is configured to receive the test signals from the diagnostic device (370; 670), and wherein the monitoring device is configured to execute, in response to receiving the test signals, a test procedure on the electrical load while the electrical load is idle or while the electrical load is in service at the respective time, the monitoring device further configured to include into a reply signal results of the test procedure on the electrical load that includes at least one of an identification of the electrical load and details of the test procedure executed on the electrical load ; wherein the diagnostic device (370; 670) is configured to receive the reply signal from the monitoring device . <EOS>