[0] Safety risks [TT] High loop impedance (step voltages) [IT] Double fault, overvoltage [TN-C] Broken neutral [TN-C-S] Broken neutral [TN-S] 
Broken neutral
L o w
O p t i o n a l
N o
H i g h e s t
H i g h
S a f e s t
B r o k e n n e u t r a l