Could any body help me im stumped.Im in ireland and im doin a city guilds course B im not worried bout the tiny differences between our irish regs and the iee regs but i wanna know whats an exceptable earth fault loop impedance what would be too much in a tncs or tt system houses. regs say Zs < Uo/Ia could anyone explain better please , i know mcbs have impedance limits what happens if you exceed the level of impedance do they not operate properly just any general knowedge will help please