Matt,
Thanks for the reply. I should have clarified, but I am talking about a
standard grid-tied, non-backup system.
I'm still not quite sure I have any solid code sections to back up my
assumption that it is OK to tie the inverter GEC to the nearest steel, rather
than running all the way back to the water main (where the utility service
entrance GEC is tied).
If we have an inverter mounted on a roof, are you saying we can or cannot go to
the closest building steel with the GEC? 690.47(C)(6) sounds like we have to go
back to the water main. While 690.47(D) sounds like we are supposed to tie to
the nearest building steel ("Grounding electrodes shall be installed... as
close as practicable to the location of roof-mounted photovoltaic arrays").
Thanks for any clarifications,
Jason M. Szrom, PE
Engineer
Solar Energy Systems, LLC
718-389-1545 x13
From: [email protected]
[mailto:[email protected]] On Behalf Of Matt Lafferty
Sent: Thursday, August 19, 2010 2:01 PM
To: 'RE-wrenches'
Subject: Re: [RE-wrenches] PV GEC to the same point as the utility service GEC?
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: [email protected]
[mailto:[email protected]] On Behalf Of Jason Szrom
Sent: Thursday, August 19, 2010 7:38 AM
To: [email protected]
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
www.solarEsystems.com<http://www.solaresystems.com/>
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