[warrenhthelines-co-nz]

Once the incident energy levels at 300mm distance exceed 1.2 Cal then a face shield would be required. What makes that energy level is (mostly) the size of the transformer and the LV network between you and that transformer (loop impedance can give you an approximation of this) and the speed that the protection will operate if a fault occurs. There are a few other factors too but those are the main ones. Once you know this you can set some basic rules of when to / not to use a face shield. Sorry I havent done the calcs for this yet as its something we need to do but once I have I am happy to share (unless someone else has already done it?)