Original Version

Rule 58.3-C1

58.3-C1)    Grounding of Windings: Transformer windings not exceeding 250 volts (except those exclusively for energizing street lighting circuits and those used exclusively for energizing signal and track circuit) shall be effectively grounded as follows:

a)    Single phase systems: In two wire (nominal 120-volt system one wire shall be grounded; in two wire (nominal 240-volt) systems where the mid-point or some intermediate point of the windings is not available, one wire shall be grounded; in two-wire (nominal 240 volt) systems where the mid-point or some intermediate point of the winding is available, that point shall be grounded; in three-wire (nominal 120/240-volt) systems, the mid-point of the winding shall be grounded.  (See App. G, Fig 57.)

b)     Two phase systems: In three-wire (nominal 240 volt) systems, the point common to both windings shall be grounded; in four-wire (nominal 120/240-volt) systems, the mid-point of the winding on one phase shall be grounded; in four wire (nominal 240-volt), and five wire (nominal 120/240-votls) systems, the mid-points of both windings shall be connected and grounded.  (See App. G, Fig. 58.)

c)    Three phase Systems: In three-wire delta (nominal 120 or 240 volt) systems the mid-point of one transformer winding shall be grounded, or if the midpoint is not available on any of the transformer windings, a point common to any two windings (one phase wire) shall be grounded; in three-wire star (nominal 120, 208, or 240 volt) systems, the point common to all windings shall be grounded or, if the common point is not available on a three-phase star-connected transformer of such a system, one of the phase wires shall be grounded; in four-wire star (nominal 120/208 volt) and three-wire T or Scott (nominal 240 volt) systems, the common point shall be grounded.  (See App. G, Fig 59.)

Strikeout and Underline Version

Rule 58.3-C1

58.3-C1)    Grounding of Windings: Transformer windings not exceeding 250 volts (except those exclusively for energizing street lighting circuits and those used exclusively for energizing signal and track circuit) shall be effectively grounded as follows:

a)    Single phase systems: In two wire (nominal 120-volt system one wire shall be grounded; in two wire (nominal 240-volt) systems where the mid-point or some intermediate point of the windings is not available, one wire shall be grounded; in two-wire (nominal 240 volt) systems where the mid-point or some intermediate point of the winding is available, that point shall be grounded; in three-wire (nominal 120/240-volt) systems, the mid-point of the winding shall be grounded.  (See App. G, Fig 57.)

b)    Two phase systems: In three-wire (nominal 240 volt) systems, the point common to both windings shall be grounded; in four-wire (nominal 120/240-volt) systems, the mid-point of the winding on one phase shall be grounded; in four wire (nominal 240-volt), and five wire (nominal 120/240-votls) systems, the mid-points of both windings shall be connected and grounded.  (See App. G, Fig. 58.)

c)    Three-Phase Systems: In three-wire delta (nominal 120 or 240 volt) systems the midpoint of one transformer winding or shall be grounded, or if the midpoint is not available on any of the transformer windings, a point common to two windings (one phase wire) shall be grounded; in three-wire star (nominal 120 208or 240 volt) systems, the point common to all windings or shall be grounded, or if the midpoint is not available on any of the transformer windings, one of the phase wires shall be grounded; in four-wire star (nominal 120/208 volt) and three-wire T or Scott (nominal 240 volts) systems, the common point shall be grounded (see App. G, Fig. 59).

d)    Where the Secondary system is grounded at any point, the grounded conductor shall be run to each service.

Final Version

Rule 58.3-C1

58.3-C1)    Grounding of Windings: Transformer windings not exceeding 250 volts (except those exclusively for energizing street lighting circuits and those used exclusively for energizing signal and track circuit) shall be effectively grounded as follows:

a)    Single phase systems: In two wire (nominal 120-volt system one wire shall be grounded; in two wire (nominal 240-volt) systems where the mid-point or some intermediate point of the windings is not available, one wire shall be grounded; in two-wire (nominal 240 volt) systems where the mid-point or some intermediate point of the winding is available, that point shall be grounded; in three-wire (nominal 120/240-volt) systems, the mid-point of the winding shall be grounded.  (See App. G, Fig 57.)

b)    Two phase systems: In three-wire (nominal 240 volt) systems, the point common to both windings shall be grounded; in four-wire (nominal 120/240-volt) systems, the mid-point of the winding on one phase shall be grounded; in four wire (nominal 240-volt), and five wire (nominal 120/240-votls) systems, the mid-points of both windings shall be connected and grounded.  (See App. G, Fig. 58.)

c)    Three-Phase Systems: In three-wire delta (nominal 120 or 240 volt) systems the midpoint of one transformer winding or, a point common to two windings (one phase wire) shall be grounded; in three-wire star (nominal 120 208or 240 volt) systems, the point common to all windings or, one of the phase wires shall be grounded; in four-wire star (nominal 120/208 volt) systems, the common point shall be grounded (see App. G, Fig. 59).

d)    Where the Secondary system is grounded at any point, the grounded conductor shall be run to each service.