Went to job today and as I was pulling cables to one side I grabbed hold of a 1.5mm t&e and it was very very warm. Traced it back from unmarked fused board and it goes to a water heater. It was on a 15amp breaker which was also very warm. Could not identify what wattage the tank carries but it isn't a large one. What size breaker and cable are these usually on? Would a 20amp 2.5mm radial be sufficient or am I looking more towards a 4mm 30 amp?