690.47 (D) Additional Electrodes for Array Grounding

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iand74

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We just did a solar job w/ roof-mounted panels. Does 690.47 (D) require an additional electrode to be run just to the arrays?

Between the inverter and the panels we have EMT conduit w/ a grounding conductor that bonds all the arrays.

From the inverter we have an electrode to the water main.

per 690.47 (C) (3): a single conductor shall be permitted to perform the multiple functions of dc grounding, ac grounding, and bonding between ac and dc systems.


per 690.47 (C) (6): a common grounding electrode shall be permitted to be used for both systems...
 

Pierre C Belarge

Senior Member
Based on Exception #2, I am going to say that an additional GEC is required to be installed, unless you meet the requirements of the exception.
 

physis

Senior Member
this is new for 2008, it's a little confusing.
A couple, three years ago I put quite a bit of effort into a proposal to essentially rewrite 690 because it's a pretty not so goodly written article. But, alas, I got hardly no feed back from the people here so I abadoned the notion.
 

iand74

Member
A couple, three years ago I put quite a bit of effort into a proposal to essentially rewrite 690 because it's a pretty not so goodly written article. But, alas, I got hardly no feed back from the people here so I abadoned the notion.
agreed, the whole article could be written more clearly.
 
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The grounding electrode connection is for lightning protection, one of my specialties. So like any other wiring system you may install, the equipment is to be gounded to ensure the principles of 250.4 (outside the system) are adhered to while equipment grounding of the system provides protection from faults within the system.
 

chris kennedy

Senior Member
I'd be interested in looking at this but I'm using 2005 and that stops at 690.47(C)
Here it is.

690.47(D) Additional Electrodes for Array Grounding. Grounding electrodes shall be installed in accordance with 250.52 at the location of all ground- and pole-mounted photovoltaic arrays and as close as practicable to the location of roof-mounted photovoltaic arrays. The electrodes shall be connected directly to the array frame(s) or structure. The dc grounding electrode conductor shall be sized according to 250.166. Additional electrodes are not permitted to be used as a substitute for equipment bonding or equipment grounding conductor requirements.
The structure of a ground- or pole-mounted photovoltaic array shall be permitted to be considered a grounding electrode if it meets the requirements of 250.52. Roof-mounted photovoltaic arrays shall be permitted to use the metal frame of a building or structure if the requirements of 250.52(A)(2) are met.
Exception No. 1: Array grounding electrode(s) shall not be required where the load served by the array is integral with the array.
Exception No. 2: Additional array grounding electrode(s) shall not be required if located within 6 ft of the premises wiring electrode.
 

physis

Senior Member
The grounding electrode connection is for lightning protection, one of my specialties. So like any other wiring system you may install, the equipment is to be gounded to ensure the principles of 250.4 (outside the system) are adhered to while equipment grounding of the system provides protection from faults within the system.
It actually has much more to do with keeping the earth at a safe potential.

A grounding electrode just isn't all that helpful against a lighting strike.

Edit: Thank you for the code reference Chris. :smile:
 
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It actually has much more to do with keeping the earth at a safe potential.

A grounding electrode just isn't all that helpful against a lighting strike.
A grounding electrode, short of surge protection, is the only way to protect against lightning, even if it doesn't always work.

Grounding electrodes can't and don't change the potential of the earth. Grounding of the array provides a path to earth for the lightning currents, while bonding of the grounding system to the structure electrical service prevents a difference of potential between systems.

I suggest you study a few of my papers on the effects of lightning through plain materials.
 

physis

Senior Member
A grounding electrode, short of surge protection, is the only way to protect against lightning, even if it doesn't always work.

Grounding electrodes can't and don't change the potential of the earth. Grounding of the array provides a path to earth for the lightning currents, while bonding of the grounding system to the structure electrical service prevents a difference of potential between systems.

I suggest you study a few of my papers on the effects of lightning through plain materials.
I appreciate that you have written papers.

A grounding electrode, short of surge protection, is the only way to protect against lightning
Surely someone who professes what you have doesn't beleive that.

Grounding electrodes can't and don't change the potential of the earth.
Really? What are those things doing anyway? Aside from pretty much nothing against lightning.

Grounding of the array provides a path to earth for the lightning currents
Do you really beleive that lightning needs you to provide it a current path? It "will" make one, with or without you. And I hope you don't expect a stupid buried conductor will help you with that.

while bonding of the grounding system to the structure electrical service prevents a difference of potential between systems.
I think that confirms what I had originally said.
 
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newenergy

Member
It is hard to figure in 2008, but no cities have required separate grounding electrodes for me in SoCal.

690.47(C) seems to make it pretty clear that the AC electrode and bonding between the AC and DC are allowed and that conductor sizing is based on the less strict 690.45.

690.47(D) makes it sound like a separate DC electrode is needed, but in this document, http://www.nmsu.edu/~tdi/pdf-resources/INSPECTOR_CHECKLIST_6-23-06.pdf , John Wiles (noted authority and authored a lot of 690) says "The 2008 NEC in 690.47 ALLOWS a
combined dc grounding electrode conductor and an ac equipment-grounding
electrode..."

One exception is if the load served by the array is integral with the array. Does it seem like this is the case with a grid-tied roof-mounted system?

Is 690.47(D) just meant to apply under the conditions of 690.47(A) and (B), which call for grounding electrodes, but not (C) which doesn't?
 

c_picard

Senior Member
"...and as close as practicable to the location of roof-mounted photovoltaic arrays"

This electrode, as I understand it, is "Supplemental"(2005) or "Auxiliary"(2008)for the purpose of lightning protection, and need not be part of the grounding electrode system(AC or DC).
Mr. Wiles has a nice illustration of this.
I agree,690 could use some clarification.

I also have concerns about installing a conductor from the roof to the electrode via a metallic conduit, wouldn't we run into that choke effect issue that usually applies to GEC's?
 

newenergy

Member
I also have concerns about installing a conductor from the roof to the electrode via a metallic conduit, wouldn't we run into that choke effect issue that usually applies to GEC's?
From searching a few posts here someone (don_resqcapt19 - http://forums.mikeholt.com/showthread.php?p=729052&highlight=choke+effect#post729052) said that there's no choke effect if you run the power conductors in the same conduit (they usually are) and that it only happens with AC, which it isn't.

Another post suggests that there's no choke effect if the ground is bonded at both sides of the raceway.
 
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