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