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