Code Change Summary: Proper methods for grounding multiple separately derived systems have been revised and expanded.
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.
In the 2014 NEC®, this section required the common GEC 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) The metal frame of the building or structure that complies with 250.52(A)(2) or is connected to the grounding electrode system by a conductor that shall not be smaller than 3/0 AWG copper or 250 kcmil aluminum.
In the 2017 NEC®, this section was revised to allow the common GEC 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.
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 2017 NEC® edition of NFPA 70.
2014 Code Language:
250.30(A)(6)
(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) The metal frame of the building or structure that complies with 250.52(A)(2) or is connected to the grounding electrode system by a conductor that shall not be smaller than 3/0 AWG copper or 250 kcmil aluminum
2017 Code Language:
250.30(A)(6)
(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
One of the following is NOT permitted to be used as a grounding electrode conductor for multiple separately derived systems. Which of the following is NOT permitted to be used as a grounding electrode conductor for multiple separately derived systems?
Please register or sign in for electrical continuing education courses. If you were already signed in, your session probably expired, please sign back in. |