690.47 Buildings or Structures Supporting a PV Array.
Code Change Summary: The rules pertaining to the grounding electrode system for a PV installation have been replaced.
The grounding electrode system requirements for a PV system under the 2014 NEC® had many gray areas. The first sentence in 690.47(B) left code readers wondering what a DC PV system really was and if the grounding requirements in that section applied at all to a PV system with DC source circuits running to an inverter with an AC output.
The previous rules in 690.47(C) were only for systems with AC and DC grounding requirements which left code readers wondering if the rules applied at all to ungrounded PV system inverters which have been known to have no common grounding electrode connection terminal to connect a grounding electrode conductor.
The previous rules in 690.47(D) were confusing because they required an additional auxiliary grounding electrode for PV systems attached to buildings that already had a grounding electrode system.
In the 2017 NEC®, the grounding electrode system requirements have been made much easier to follow. Now, it is clear that a building or structure “supporting” a PV array shall have a grounding electrode system installed in accordance with Part III of Article 250. The additional auxiliary grounding electrode previously required in 690.47(D) has been relocated to 690.47(B) and is now “permitted” rather than required.
Another change occurred by separating the grounding rules into two categories; Grounding requirements for PV systems that are solidly grounded and grounding requirements for those that are not, such as a functional grounded PV system.
The new definition in 690.2 defines a Functional Grounded PV System as a PV system that has an electrical reference to ground that is not solidly grounded. This describes many PV systems in existence today since most grounded PV systems establish a ground reference through a resistor or fuse that is part of the ground-fault protection system required in 690.41(B). See the new informational note after 690.47(A) in the NEC® for additional details.
Below is a preview of the NEC®. 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:
See actual NEC® text for sections 690.47(A) through (D).
2017 Code Language:
690.47 Grounding Electrode System.
(A) Buildings or Structures Supporting a PV Array. A building or structure supporting a PV array shall have a grounding electrode system installed in accordance with Part III of Article 250.
PV array equipment grounding conductors shall be connected to the grounding electrode system of the building or structure supporting the PV array in accordance with Part VII of Article 250. This connection shall be in addition to any other equipment grounding conductor requirements in 690.43(C). The PV array equipment grounding conductors shall be sized in accordance with 690.45.
For PV systems that are not solidly grounded, the equipment grounding conductor for the output of the PV system, connected to associated distribution equipment, shall be permitted to be the connection to ground for ground-fault protection and equipment grounding of the PV array.
For solidly grounded PV systems, as permitted in 690.41(A)(5), the grounded conductor shall be connected to a grounding electrode system by means of a grounding electrode conductor sized in accordance with 250.166.
N (B) Additional Auxiliary Electrodes for Array Grounding. Grounding electrodes shall be permitted to be installed in accordance with 250.52 and 250.54 at the location of ground and roof-mounted PV arrays. The electrodes shall be permitted to be connected directly to the array frame(s) or structure. The grounding electrode conductor shall be sized according to 250.66. The structure of a ground-mounted PV array shall be permitted to be considered a grounding electrode if it meets the requirements of 250.52. Roof mounted PV arrays shall be permitted to use the metal frame of a building or structure if the requirements of 250.52(A)(2) are met.