@ Chris480, @ Spir Georges GHALI: yes several manufacturers propose some fault localization systems. Generally, to have a balance between initial investment costs and fault localtion costs, the torroids are installed from the beginning, but only on the main circuits. These torroids are connected to the fault detection modules which enable to know instantly on which main circuit the fault is located. Then maintenance people just have to focus on the secondary circuits of that zone, and use clamp meters to find the exact location of the fault, which is faster and easier as secondary circuits have smaller cables. Of course, it is always possible to install more torroids and fault detection modules, to make the fault detection even faster.