Maximum Zs values in a TT earthing system
The maximum disconnection times for a TT system is 0.2 seconds for final circuits up to and including 32A (Table 41.1) and for distribution circuits or circuits greater than 32A it’s 1 second (411.3.2.4). The problem is that with TT systems the external loop impedance value (Ze) will be too high to achieve these 0.2 … Read more