Grounded Electrode Conductor (GEC)

DOE-HDBK-1092-98

4.7 GROUNDING ELECTRODE CONDUCTOR (GEC)

The main purpose of the grounding electrode conductor (GEC) is to connect the electrical system to

earth ground. The GEC actually provides three grounding paths to the grounding electrode system.

They are as follows:

1. The grounded conductor path

2. The equipment grounding path

3. The bonding path.

In grounded systems, the GEC connects to the neutral bar in the service equipment enclosure. In

ungrounded systems, the GEC connects to the grounding terminal bar. It grounds the following items

to the grounding electrode system:

1. The grounded conductor, if present

2. The equipment grounding conductor, if present

3. The metal of conduits, if present

4. The metal of enclosures, if present

5. The bonding jumpers bonding together metal enclosures and conduits

6. The metal enclosure of the service equipment.

4.7.1

SIZING THE GROUNDING ELECTRODE CONDUCTOR

NEC Section 250-94 requires the grounding electrode conductor to be sized by the circular mils

rating of the largest service entrance conductor or conductors and selected from NEC Table 250-94

based on these values.

For example, the size of the service entrance conductors from a delta, three-phase, four-wire

midpoint tap is #250 kcmil, THWN copper for phases A and C, #2/0 for phase B, and #1/0 for the

neutral. What size copper GEC is required to ground this system to a metal water pipe?

Step 1:

Finding the largest phase--NEC 250-94 #250 kcmil is the largest phase

Step 2:

Finding the size GEC--NEC Table 250-94 #250 kcmil requires #2 cu

Answer:

The size of grounding electrode conductor (GEC) is at least #2 copper.

Note: NEC Table 250-94 is used to size the grounding electrode conductor for both grounded and

ungrounded systems. The table is used where the grounding electrode conductor is connected to a

metal water pipe or the metal frame of building steel.

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