[0] Risk of broken neutral [IT] No [TN-S] High [TN-C] Highest [TN-C-S] High [TT] 
No
H i g h
Y e s
L o w
N o
S a f e
L e a s t
H i g h l o o p i m p e d a n c e ( s t e p v o l t a g e s )
S a f e a n d r e l i a b l e