The CT-3A-RS is a three-phase dual range, 0.5A to 60A, 4A to 400A, current data logger that just needs its clamp-on current transformers connected to your incoming supply.  Setup the Logger using the Electrosoft software, then fit it to the distribution board or other point that you're going to measure. CT’s fit around 30mm diameter cables.
 
As no voltage input is required, you can fit easily as a competent person without necessarily requiring an electrician or engineer, and may not require any power interruption at all.  Once you're set up, just press the Start button to start logging!  The onboard indicator will flash Green when logging.
 
When the logger's finished recording (or you've captured enough data!) just disconnect from supply, hook it up to your PC and download the information.  Electrosoft will let you view the data immediately on-screen and save or export for later analysis.