Grounding Electrode System - hdbk109220040060

DOE-HDBK-1092-2004

4.13 GROUNDING ELECTRODE SYSTEM

If 10 feet or more of metal water pipe is in the earth, the water pipe is considered the grounding

electrode, but it shall be supplemented by an additional electrode. NEC 250.50 lists four types

of electrodes. If one or all are available, they shall be bonded together to make up the grounding

electrode system. The bonding jumper that connects these electrodes shall be at least as large

as the grounding electrode conductor of the system sized by NEC Table 250.66. The four types

of electrodes are as follows:

Metal water pipe in contact with the earth for 10 feet or more. Interior metal water pipe

beyond 5 feet from the water entrance shall not be used as a part of the grounding

electrode system or as a conductor to interconnect those electrodes.

Metal frame of the building, where effectively grounded

Bare #4 conductor at least 20 feet in length and near the bottom of the concrete foundation

(within 2 inches), or -inch reinforcing steel or rods at least 20 feet in length (one

continuous length or spliced together)

Bare #2 conductor encircling building at least 2 feet in the ground (spliced together at

each end).

The grounding electrode conductor at the service equipment can be connected to any

convenient interbonded electrodes that provide a solid, effective connection. Metal water pipe

shall be supplemented by an additional electrode, which can be any of the following electrodes:

Rod

Pipe

Plate

Building steel

Concrete-encased electrode.

(See Figure 4-8, which lists some of the different types of grounding electrodes.)

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