A power distribution unit comprising; a power distribution unit housing disposable in an electrical equipment rack of the type in which a plurality of electrical components are removably mountable; a power input penetrating the housing; a voltage sensor; a plurality of power outputs disposed in the housing, each in electrical communication with the power input and each connectable to a respective electrical load; a plurality of current sensors, each in electrical communication with one of the power outputs; and a power monitoring section having an analog-to-digital converter in electrical communication with the voltage sensor and the current sensors, processing logic in electrical communication with the ADC, and a memory in electrical communication with the processing logic; wherein the ADC is responsive to signals provided by the sensors to sample the signals and obtain samples of voltage and current over one or more cycles of input power which samples are stored in the memory; and wherein the processing logic is configured to calculate raw RMS values of voltage and current from the samples, scale the raw RMS values according to a predetermined calibration factor to obtain calibrated RMS voltage and current values, and characterised in that the processing logic is further configured to compare samples of voltage and current obtained with respect to at least one of the electrical loads during a first cycle of input power with: (i) model samples stored in the memory and representing the at least one of the electrical loads, or (ii) historical samples of voltage and current obtained with respect to the at least one of the electrical loads during a second cycle of input power, and generate an alert signal if there is a difference of predetermined magnitude therebetween. a power distribution unit housing disposable in an electrical equipment rack of the type in which a plurality of electrical components are removably mountable; a power input penetrating the housing; a voltage sensor; a plurality of power outputs disposed in the housing, each in electrical communication with the power input and each connectable to a respective electrical load; a plurality of current sensors, each in electrical communication with one of the power outputs; and a power monitoring section having an analog-to-digital converter in electrical communication with the voltage sensor and the current sensors, processing logic in electrical communication with the ADC, and a memory in electrical communication with the processing logic; wherein the ADC is responsive to signals provided by the sensors to sample the signals and obtain samples of voltage and current over one or more cycles of input power which samples are stored in the memory; and wherein the processing logic is configured to calculate raw RMS values of voltage and current from the samples, scale the raw RMS values according to a predetermined calibration factor to obtain calibrated RMS voltage and current values, and characterised in that the processing logic is further configured to compare samples of voltage and current obtained with respect to at least one of the electrical loads during a first cycle of input power with: (i) model samples stored in the memory and representing the at least one of the electrical loads, or (ii) historical samples of voltage and current obtained with respect to the at least one of the electrical loads during a second cycle of input power, (i) model samples stored in the memory and representing the at least one of the electrical loads, or (ii) historical samples of voltage and current obtained with respect to the at least one of the electrical loads during a second cycle of input power,