"The purpose of this Guide is: To review grounding practices with especial. rderence to safety. To establish@ as a basis for design@ the safe limits for potential differences which can exist in a station@' under fault conditions@ between points which can be contacted .by the human body. To prm??ide a step by step guide for the design of practical grounding systems based 011 these limits. To recommend test methods for obtaining data for the design of ground systems@ .:and for verifying the- adequacy of ground systems as constructed. To develop mathematical methods as an aid in the understanding and solution of typical ground gradient problems. To make= anilable in English translation@ some of th~ more pertin~nt and valuable foreign language .articl~s. To provid~ a eomprehemive bibliography@ with abstracts@ of ex is tin~ literature rela!ed to the subject@ for the benefit of those seeking additional iniornlltion not included herein. This Guide@ as a whole@ is primarily concerned ??with <1lternating-current outdoor substation installations. A few sections are applic:or.ble to indoor portions of such stations or to stations which are wholly indoors. Obviously. the same ground gradient problems which e;lCiH in a substation yard will not be present within a building@ provided the floor either furnishes an effectiH insulation from earth potentials@ or else is effectively equivalent to a conducting p!J.te or close mesh grid@ which is always at st<~tion ground potential; and pru??ided also that the conducting parts of the building structure .and fixtures are kept at st:or. ??tion ground potentia!. However@ even in 'the case of a wholly indoor substation@ it may be necessary to consider some of the possible hazards mentionecl herein front ""perimeter gradients"" (at building entrances)@ and from transferred pOtentials. This applies primarily@ of course@ to large capacity utility substations where the station ground system may rise to a high potential during a fault. This Guide does not attempt to cover the many special grounding problems peculiar to direct current substations@ which are discussed elsewhere in the literature.'' Finally@ this Guide makes no attempt to develop a quantitative analysis of !he effects of lightning surges. To cover this fully would require another report of nearly equal size. Appendix In ... nd the -references@ however@ contain much information on this. At this point it will merely be stated that the greater impedance offered to steep wave front~""Surges will increase the drop in ground leads to _the grid system@ and decrease the effectiveness of the more distant parts of the grid. Offsetting this in :large degree@ is the fact that the body can apparently tolerate far g@-eater current magnitude in the case of surges than in the case of 60 cycles. As a practical matter@ it is fe:t that:. ground systems designed as recommended herein will:give a high degree of protection against steep wave front surges entering the station and passing to earth through its grounding ?? system. Obviously@ a man can be killed by a direct stroke inside the station@ just as he .. can outside."