kkl
Member
- Location
- Canon City, CO
Please forgive yet another grounding question, but I couldn't find an answer to this (I don't think the forum's search function is working since a search for "690.47" found no results, even though I found it reading a post.) A revised section 690.47 - Grounding Electrode System in the 2011 NEC says:
(C) Systems with Alternating-Current and Direct-Current Grounding Requirements
...
The dc grounding system shall be bonded to the ac grounding system by one of the methods in (1), (2), or (3)
...
(2) Common Direct-Current and Alternating-Current Grounding Electrode. A dc grounding electrode conductor of the size specified by 250.166 shall be run from the marked dc grounding electrode connection point to the ac grounding electrode. Where an ac grounding electrode is not accessible, the dc grounding electrode conductor shall be connected to the ac grounding electrode conductor in accordance with 250.64(C)(1). This dc grounding electrode conductor shall not be used as a substitute for any required ac equipment grounding conductors.
(3) Combined Direct-Current Grounding Electrode Conductor and Alternating-Current Equipment Grounding Conductor. An unspliced, or irreversibly spliced, combined grounding conductor shall be run from the marked dc grounding electrode conductor connection point along with the ac circuit conductors to the grounding busbar in the associated ac equipment. This combined grounding conductor shall be the larger of the sizes specified by 250.122 or 250.166 and shall be installed in accordance with 250.64(E).
A comment in the Handbook says:
The two grounding systems are to be bonded together or have a common grounding electrode so that all ac and dc grounded circuit conductors and equipment grounding conductors have the same near-zero potential to earth. The combined dc equipment grounding, dc system grounding, and ac equipment grounding required by this section establishes only one grounding circuit and connection for the entire PV system from the PV array to the ac point of connection.
So...does this mean:
1. A DC-side grounding rod is not required, that both the array (dc equipment ground) and the negative conductor (dc system ground per 690.41) at the inverter connections can be wired back to the ac service entrance ground?
2. Why couldn't the the inverter's dc grounding point just be jumpered over to the ac grounding point, since the ac grounding wire is headed back to the same ac ground rod via the service panel?
I'm confused because of reading many comments previously about always having a dc ground rod and never tying the ac and dc grounds together.
(C) Systems with Alternating-Current and Direct-Current Grounding Requirements
...
The dc grounding system shall be bonded to the ac grounding system by one of the methods in (1), (2), or (3)
...
(2) Common Direct-Current and Alternating-Current Grounding Electrode. A dc grounding electrode conductor of the size specified by 250.166 shall be run from the marked dc grounding electrode connection point to the ac grounding electrode. Where an ac grounding electrode is not accessible, the dc grounding electrode conductor shall be connected to the ac grounding electrode conductor in accordance with 250.64(C)(1). This dc grounding electrode conductor shall not be used as a substitute for any required ac equipment grounding conductors.
(3) Combined Direct-Current Grounding Electrode Conductor and Alternating-Current Equipment Grounding Conductor. An unspliced, or irreversibly spliced, combined grounding conductor shall be run from the marked dc grounding electrode conductor connection point along with the ac circuit conductors to the grounding busbar in the associated ac equipment. This combined grounding conductor shall be the larger of the sizes specified by 250.122 or 250.166 and shall be installed in accordance with 250.64(E).
A comment in the Handbook says:
The two grounding systems are to be bonded together or have a common grounding electrode so that all ac and dc grounded circuit conductors and equipment grounding conductors have the same near-zero potential to earth. The combined dc equipment grounding, dc system grounding, and ac equipment grounding required by this section establishes only one grounding circuit and connection for the entire PV system from the PV array to the ac point of connection.
So...does this mean:
1. A DC-side grounding rod is not required, that both the array (dc equipment ground) and the negative conductor (dc system ground per 690.41) at the inverter connections can be wired back to the ac service entrance ground?
2. Why couldn't the the inverter's dc grounding point just be jumpered over to the ac grounding point, since the ac grounding wire is headed back to the same ac ground rod via the service panel?
I'm confused because of reading many comments previously about always having a dc ground rod and never tying the ac and dc grounds together.