[0] Safety [IT] Less Safe [TN-S] Safest [TN-C] Least Safe [TN-C-S] Safe [TT] 
Safe
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