2011 National Electrical Code Changes

25. 690.47 Grounding Electrode System

The requirements for PV grounding electrode systems have been greatly revised.

690.47 Grounding Electrode System.

(B) Direct-Current Systems. If installing a DC system, a grounding electrode system must be provided in accordance with 250.166 with a grounding electrode conductor in accordance with 250.64.

A common DC grounding-electrode conductor is permitted to serve multiple inverters with the size of the common grounding electrode and the tap conductors in accordance with 250.166. The tap conductors must be connected to the common grounding-electrode conductor in such a manner that the common grounding electrode conductor remains without a splice or joint.

(C) Alternating-Current (AC) and Direct-Current (DC) Grounding Requirements. PV systems with DC modules having no direct connection between the DC grounded conductor and AC grounded conductor must be bonded to the AC grounding system by one of the methods listed in (1), (2), or (3).

Note 1: ANSI/UL 1741, Standard for Inverters, Converters, and Controllers for Use in Independent Power Systems have the grounding electrode conductor (GEC) connection point identified. In PV inverters, the terminals for the DC and AC equipment grounding conductors common with each other are marked DC GEC terminal.

Note 2: For utility-interactive systems, the existing premises grounding system serves as the AC grounding system.

(1) Separate DC Grounding Electrode System Bonded to the AC Grounding Electrode System. A separate DC grounding electrode bonded to the AC grounding electrode system with a bonding jumper sized to the larger of the existing AC grounding electrode conductor or DC grounding electrode conductor specified by 250.166.

The DC grounding electrode conductor or bonding jumper to the AC grounding electrode system can’t be used as the required AC equipment grounding conductor.

(2) Common DC and AC Grounding Electrode. A DC grounding electrode conductor sized in accordance with 250.166 run from the marked DC grounding electrode connection point to the AC grounding electrode. (click here to see Fig. 21)

Where an AC grounding electrode isn’t accessible, the DC grounding electrode conductor is permitted to terminate to the AC grounding electrode conductor by irreversible compression-type connectors listed as grounding and bonding equipment or by the exothermic welding process [250.64(C)(1)].

The DC grounding electrode conductor or bonding jumper to the AC grounding electrode system can’t be used as the required AC equipment grounding conductor.

(3) Combined DC Grounding Electrode Conductor and AC Equipment Grounding Conductor. An unspliced, or irreversibly spliced, combined equipment grounding/grounding electrode conductor run from the marked DC grounding electrode connection point along with the AC circuit conductors to the grounding bus bar in the associated AC equipment.

The combined equipment grounding/grounding electrode conductor must be sized to the larger of 250.122 or 250.166 and be installed in accordance with 250.64(E).

Analysis: Section 690.47(B) has been revised to clarify that a common grounding electrode conductor can be used to ground multiple inverters. This concept isn’t new to the Code, as similar provisions can be found in 250.30 for separately derived systems.

As can be seen rather easily, (C) has been extensively revised again. Changes to this edition of the NEC are intended to incorporate the concepts of the 2005 and 2008 editions into clear, easily understandable text.

In a somewhat surprising change, 690.47(D) was deleted. That section required that ground and pole-mounted PV arrays have a grounding electrode. This requirement was added in the 2008 edition and was intended to be optional. The Code language that was used, however, made it mandatory. By removing the rule altogether, it’s still optional, but now isn’t mandatory.