[RE-wrenches] PV GEC to the same point as the utility service GEC?

Matt Lafferty gilligan06 at gmail.com
Thu Aug 19 11:01:14 PDT 2010


Good questions, Jason. 
 
No. Yes (2008 NEC 690.47(C) & (D)).
 
Alternative considerations that might result in a "maybe": Does the system
in question have storage (i.e. batteries)? Is your POCC on a Delta system?
(your hi-rise example says Wye... But if it is directly tied to a Delta
system, you might gotta run back to basement.)
 
If you are talking about a standard, grid-tied, non-backup system, and the
AC distribution between your tie-in and the utility is suitably sized for
the PV, you should hit the GE system where your AC system is getting it's
neutral bond. (Closest steel OK for PV grounding electrode.) Equipment
ground, same thing. Be sure to run an equipment grounding conductor from the
inverter to the array (i.e. don't just bond the rack to building steel). 
 
Regarding your Additional Info items:
1. Yep.
2. Some people on this list and in the AHJ community would argue that the AC
side of the inverter in this case IS a separately derived system in all
cases (I'm not among that bunch). Either way, the output of your entire
system is going thru the building's AC distribution system. ESPECIALLY if
you are on the secondary of a WYE xfrmer, you can and SHOULD source your PV
GEC where the xfrmer neutral is bonded. 
3. You are right. The various provisions of 690.47(C) allow/require this. In
particular, (C)5 & 6.
 
The underlying principle that counts here is, "Get your GEC where your AC
source gets its system ground." 
 
Matt "I'm no building inspector" Lafferty

  _____  

From: re-wrenches-bounces at lists.re-wrenches.org
[mailto:re-wrenches-bounces at lists.re-wrenches.org] On Behalf Of Jason Szrom
Sent: Thursday, August 19, 2010 7:38 AM
To: re-wrenches at lists.re-wrenches.org
Subject: [RE-wrenches] PV GEC to the same point as the utility service GEC?



Wrenches,

 

Questions:  Does the PV GEC have to be bonded to the ground electrode system
at the same point as the utility service equipment GEC? Is there a code
section to back this up?

 

Additional info:

1.       The DC side of the inverter is a separately derived system and
therefore needs a GEC to a ground electrode.

2.       The AC side of the inverter is not a separately derived system
therefore 250.30(A)(7) does not apply. This section states that AC
separately derived systems should be grounded to the nearest ground
electrode (building steel in many cases) and therefore does not need to be
bonded to the same point as the utility service GEC.

3.       My thought process is this:  The PV GEC can be bonded to the
nearest ground electrode as long as this electrode is tied to the same
ground electrode as the utility service electrode, forming one complete
'ground electrode system'. My opinion is that this setup is analogous to
this example which is regularly seen in the field.  High rise building with
structural steel bonded to water main with utility service GEC bonded as
well. Delta-wye step-down transformer on an upper level with the derived
neutral on the secondary bonded to closest building steel. Yet there is
still an equipment grounding connection to both the primary and secondary
sides of the transformer. This implies that it is OK and even preferable to
tie the PV GEC to the nearest ground electrode,  but I can't find any
evidence or section in the code that confirms or denies this.

 

Thanks for any input,

Jason

 

Jason M. Szrom, PE

Engineer

 

Solar Energy Systems, LLC

1205 Manhattan Ave

Suite 1210

Brooklyn, NY 11222

 

718-389-1545 x13

 <http://www.solaresystems.com/> www.solarEsystems.com

 

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