[0] Advantages [TT] Safe and reliable [IT] Continuity of operation, cost [TN-S] Safest [TN-C] Cost [TN-C-S] 
Safety and cost
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