The EC-2VA is a single-phase voltage and current data logger that uses a flexible Rogowski coil and plug to connect to the mains supply/equipment you wish to measure.  Setup the Logger using the Electrosoft software, then fit it to the distribution board or other point that you're going to measure.
 
This logger is designed to be installed by a competent person (generally an electrician or engineer), and if isolated test points or a mains socket are available can be fitted without power interruption.  Once you're set up, it'll start logging automatically as soon as voltage is detected!  The 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.