i was once chasing ( making a groove for a cable ) in the kitchen before tiling
now you allways have electical wires in straight drops DOWN, i got my tester and found the drops for the 2 sockets and the cooker point, i marked them on the wall to know where to avoid, i quickly scanned the wall for anything else, it was all clear
so i start chasing the wall out and BANG, i had chopped though a spur off the 40 amp cooker cable ( some clown had make a spur for the power shower

) it sent me flying across the kitchen, i lifted me off my feet and sent me 3 M away, the bolster chisel was 2 inch wide and thick, it had blown a hole in it about the size of a golf ball
i was lucky to live to be honest
these days, i allways give the advice, dont mess about with 240 V electricity