When you purchase Wattson you will be provided with a single sensor clip. Most houses in the UK use single phase electricity and only require one clip to measure.Some premises may have 3- phase electricity installed, this is normally for houses with larger electricity loads and most businesses.

To measure three phase electricity you will need to purchase 2 extra clips.You will also need an additional sensor clip if you are generating your own energy at your site from either solar panels or wind generators