Direct Grid Tie Ground Wire [RE-wrenches]

Wed Apr 16 09:33:29 PDT 2008

Erika,

#1 For arrays flat and close to the a roof, it has been understood that the
modules themselves can provide physical protection to the EGC, but
obviousluy they have to be "under" the module frame, not "on the side" of
the frame.

#2 The neg DC system grounding occurs at the point where the the grounded DC
conductor is connected to the GEC/GE, not at the point of connection of the
EGC to the module frame.

#3 The cat got out of the bag in 2008 on this one.  Wiles had specific
language stating that the array frame equipment ground conductor be
connected to a stand-alone GE.  Other folks got ahold of that and insisted
that the stand-alone GE be bonded to the exist premise GE system.  I am not
sure yet if folks are trying to change this back for 2011.

I am sticking with #8 STD, installed underneath the frames for protection.
I guess some folks are opposed to using STD in any outdoor application
because moisture can get in between the strands and corrode the conductor.
I am not so sure that this is a significant problem with #8 - 7 Strand bare
copper.

Mark Frye
Berkeley Solar Electric Systems
271 Vistamont Dr
Grass Valley CA 95945
(530) 401-8024
www.berkeleysolar.com 

-----Original Message-----
From: Erika Weliczko [mailto:erika at repowersolutions.com] 
Sent: Wednesday, April 16, 2008 10:09 AM
To: RE-wrenches at topica.com
Subject: RE: Direct Grid Tie Ground Wire [RE-wrenches]

I have similar questions on the DC side about GEC, GE, equip grd. And this
also pertains to the recent thread about array equipment conductor.

Question #1:
In 690.47(D) requiring a grounding electrode for the array frame(s) or
structure there is a line about not allowing this to be a substitute for the
equipment grounding conductor. This seems to imply a #6 from some
frame/structure point to the GE. If not, then we need to run #6 from module
to module if it is exposed or as described in 690.46, which basically says
use #6 unless not exposed to damage. Is this an overkill interpretation?

Question #2: The talk in this section (690.47(D)) is about GEC and GE, so
are we performing negative bond at the array?

Question #3: Nothing stated explicitly here, but now we need to bond this GE
to the others in existence probably. 

Question #4: Then what about the GFPs? If this disables the GFP which is now
required, we need to adjust the equipment ground based on 690.45 which under
most situations #8 will meet if two times the conductor ampacity is 25
or30Ax2 (assuming #10 with some temp/fill adjustment). So are we running a
EGC? Why bother if the entire array frame/structure is bonded to the GE at
the array? And are we basically installing systems with no GFP?

I'm sorry for the insane list of questions.
I think I'm going to buy a bunch of bare solid #6 the next time prices dip.

Peace,
Erika
*********************
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-----Original Message-----
From: Drake Chamberlin [mailto:Drake.Chamberlin at redwoodalliance.org]
Sent: Monday, April 07, 2008 8:04 PM
To: RE-wrenches at topica.com
Subject: Direct Grid Tie Ground Wire [RE-wrenches]

Hello Wrenches,

I've been reading the 2008 code and talking to an inspector who is 
studying 690 very thoroughly.  A question arises about the grounding 
conductor between the AC service panel and the inverter.  Is it an 
equipment grounding conductor or a grounding electrode conductor, or both?

It would need to be both if there were both AC and DC systems.  This 
is covered in 690.47(C), "Systems with Alternating-Current and 
Direct-Current Grounding Requirements."  Unless the array had plastic 
frames, it would seem that there would always be DC grounding 
requirements, so what does this mean?

This is direct grid tie with no DC loads.  It seems another section 
would need to be added to deal with a direct grid tie system.

The main issue that arises from this is that if the ground wire is 
considered a grounding electrode conductor, it needs to be #8.  This 
would mean that a 10/3 WG cable would need to have a separate ground 
wire run that is at least #8.  It would probably be easier to run a 
#6 since it can be run of the surface.

How have you and your inspectors been interpreting this?

Thanks,

Drake 

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