Separate Equipment Grounding Conductors

DOE-HDBK-1092-2004

For example: What size THWN copper equipment grounding conductor is required to be run in a

raceway with a 70 A overcurrent protection device protecting the circuit?

Step 1:

Finding EGC - NEC Table 250.122, 70 A OCPD requires #8 copper

Answer: The equipment grounding conductor is required to be at least #8 THWN copper.

4.10.2 SEPARATE EQUIPMENT GROUNDING CONDUCTORS

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

equipment grounding conductors within raceways.

The separate 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

separate 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 250.134(B) requires 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 separate 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 sole 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.

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