Ground Loop Prevention [RE-wrenches]

[Ray Walters]

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Yes, it does create an induction loop. I pointed this out to John  
WIles during his code presentation. He didn't have a good answer.  
Code by itself is not always safe, its just the code. A room full of  
inspectors didn't even care about this potential safety hazard. In my  
experience, lightning damage is our number one problem. Meanwhile on  
this list, we discuss sometimes very mundane code issues that I've  
never seen translate to actual dangerous situations.

I'm always wary when grounding the inverter chassis: there's a lug on  
the DC side and another on the AC. I've started not using the DC lug,  
and ground the chassis on the AC side. If the AC to DC grounding  
conductor just runs from one rod to the other, and the inverter  
chassis is only bonded on one side (and Neutral is not bonded to  
ground in the inverter), I think you are avoiding a complete loop. As  
soon as you use both inverter ground lugs though, the inverter  
chassis closes the loop.

At the array, we have a separate ground rod, but we run only a single  
grounding conductor (with the array conductors) back to the power  
equipment, thus no loop. Array ground rod is bonded to this grounded  
conductor along with all other exposed metal (pole, frame, j box,  
etc.), all requirements are met. There was a question on the list  
earlier about running this grounding conductor in or out of the  
conduit. Some of us thought that running the ground wire outside the  
conduit (bare # 6) would enhance conductivity to ground, but code  
seems to indicate the ground wire needs to run with the other array  
conductors.  That particular issue would be between you and the AHJ.

Based on studying grounding books like Polyphasors's  book,  
connecting everything together is good, but each rod, metal etc.  
comes to one central point to bond, never any loops. They have  
systems with 30 or more ground rods radiating out in a star pattern,  
but NOT interconnected except at the central point. I try to use this  
concept on all our work.

Ray Walters

On May 28, 2007, at 11:38 AM, Drake Chamberlin wrote:

>
> Hello Wrenches,
>
> Article 690.47 (C) of the NEC requires that the DC grounding  
> electrode conductor connect to the grounding electrode of the AC  
> system, where DC and AC systems are present.  Or, a separate DC  
> grounding electrode may be installed, which is then bonded to the  
> AC system grounding electrode.
>
> If an inverter is feeding the grid (such as an Outback with backup  
> system) it will have an equipment grounding conductor that connects  
> to the neutral bar of the service.  It will also have a grounding  
> electrode conductor that makes a loop to the ground rods, separate  
> from the equipment grounding conductor, and also connects to the  
> neutral bar.  The equipment grounds and the grounding electrode  
> conductor connect to the equipment grounding bar in the DC disconnect.
>
> Doesn't this create an induction loop that could bring lightning  
> surges into the RE equipment and the building electrical system?
>
> A similar case, that would seem especially problematic, is a ground  
> wire run to a ground rod from an array.  It is often required to  
> bond this rod to the existing system ground rods.
>
> The array is required to have an equipment grounding conductor run  
> back to the DC equipment ground?   This will ultimately connect to  
> the utility service neutral bar. This creates a loop.
>
> Is this really the best way, technically, to ground systems?  With  
> this requirement, how do we both meet code and avoid creating a  
> grounding loop that will attract lightning surges?
>
> Thanks,
>
> Drake
>
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R. Walters
Solarray.com
NABCEP # 04170442	




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