Separate Equipment Grounding Conductors

DOE-HDBK-1092-98

4.10.2 SEPERATE EQUIPMENT GROUNDING CONDUCTORS

The possibility of worker exposure to electric shock can be reduced by the use of seperate equipment

grounding conductors within raceways.

The seperate equipment grounding conductors contribute to equalizing the potential between

exposed noncurrent-carrying metal parts of the electrical system and adjacent grounded building

steel when ground faults occur. The resistance (inductive reactance) of the ground fault circuit

normally prevents a significant amount of ground fault current from flowing through the seperate

equipment grounding conductors.

Ground fault current flows through the path that provides the lowest ground fault circuit impedance.

Fittings and raceway systems have been found that are not tightly connected or are corroded which

prevents good continuity. Therefore, the equipment grounding conductor shall be the path for the

fault current to travel over and clear the overcurrent protection device protecting the circuit.

NEC Sections 300-3(b) and 250-57(b) require the equipment grounding conductors to be routed in

the same raceway, cable, cord, etc., as the circuit conductors. All raceway systems should be

supplemented with seperate equipment grounding conductors.

Note: The equipment grounding conductor shall be routed with supply conductors back to the source.

Additional equipment grounding may be made to nearby grounded structural members or to

grounding grids, but this shall not take the place of the co-routed equipment grounding conductors.

Raceway systems should not be used as the grounding conductor.

4.11 UNGROUNDED SYSTEMS

Three-phase, three-wire, ungrounded systems (DELTA), which are extensively used in industrial

establishments, do not require the use of grounded conductors as circuit conductors.

The same network of equipment grounding conductors shall be provided for ungrounded systems as

for grounded systems. Equipment grounding conductors are required in ungrounded systems to

provide shock protection and to present a low-impedance path for phase-to-phase fault currents in

case the first ground fault is not located and cleared before another ground fault occurs on a different

phase in the system.

Grounding electrode conductors and bonding jumpers shall be computed, sized, and installed in the

same manner as if the system were a grounded system. Apply all the requirements listed in Sections

4.6 through 4.8 for sizing the elements of an ungrounded system.

4.12 GROUNDING A SEPARATELY DERIVED SYSTEM

NEC Sections 250-5(d) and 250-26 cover the rules for grounding separately derived systems. The

system grounding conductor for a separately derived system shall be grounded at only one point. That

single system grounding point is at the source of the separately derived system and ahead of any

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