If an impedance Zi is inserted in series with each of the three lines and N is inserted in the neutral B VNn-y Nn bn Z,+ P Nn 十 0 十 L 3 +ontv Nn L 十 十 P PIf an impedance ZL is inserted in series with each of the three lines and ZN is inserted in the neutral. + = 0 + − + + − + + − • • • • • • • N Nn L p Nn cn L p Nn bn L p Nn an Z V Z Z V V Z Z V V Z Z V V ) 0 3 1 ( = + + + + = + • • • • L p a n b n cn L p N N n Z Z V V V Z Z Z V  = 0 • V Nn    a b c n • V an • + + + − − −    A B C • Z p Z p Z p N V bn • V cn • ZL ZL ZN ZL