Section 250.30(A)(6) provides details on using a common grounding electrode conductor (GEC) and individual grounding electrode conductor taps in order to properly bond multiple separately derived systems. The NEC^® does not specifically require a common GEC but using this method results in the least amount of wire and labor. If a common GEC is used, the rules in 250.30(A)(6) will apply.

According to 250.30(A)(6), a common GEC must be one of the following:

(1) A conductor of the wire type not smaller than 3/0 AWG copper or 250 kcmil aluminum.

(2) A metal water pipe that complies with 250.68(C)(1).

(3) The metal structural frame of the building or structure that complies with 250.68(C)(2) or is connected to the grounding electrode system by a conductor not smaller than 3/0 AWG copper or 250 kcmil aluminum.

• In order to use item 2 above, the water pipe must comply with 250.68(C)(1) which means it must qualify as a grounding electrode and be connected to within the first 5 feet from the point of entrance to the building.
• In order to use item 3 above, the code language makes it clear that the metal frame of the building must be “structural”. As well, the structural metal must comply with 250.68(C)(2) which provides the rules to follow when using the structural steel as conductor to interconnect electrodes.

Below is a preview of Article 250. See the actual NEC^® text at NFPA.ORG for the complete code section. Once there, click on their link to free access to the 2020 NEC^® edition of NFPA 70.

2020 Code Language:

250.30(A)(6) Grounding Electrode Conductor, Multiple Separately Derived Systems.

(a) Common Grounding Electrode Conductor. The common grounding electrode conductor shall be permitted to be one of the following:

(1) A conductor of the wire type not smaller than 3/0 AWG copper or 250 kcmil aluminum

(2) A metal water pipe that complies with 250.68(C)(1)

(3) The metal structural frame of the building or structure that complies with 250.68(C)(2) or is connected to the grounding electrode system by a conductor not smaller than 3/0 AWG copper or 250 kcmil aluminum