In connection way of surge-arrester, the term of distance to protected subject is important. Generally mention has already been made of the desirability of connecting the surge arrester as close as possible to the equipment it is intended to protect. It is also important that the neutral end should have a low resistance connection to earth of adequate cross-sectional area. At currents of 10 kA or more, any resistance in these connections will mean a significant additional voltage is seen at the transformer terminals over and above the nominal protection level of the arrester. Below figure shows a typical installation adjacent the HV terminal of a substation transformer. The lengths L, a1 and a2 must be kept as short as possible. In your concerned subjects, each chosen connection which aid you to obtaining of shortest and straightest connection ( for decreasing of surge impedance) is more desirable. 