Grounding advice for small off-grid PV installation?

 Hello-

I'm putting in a small PV system at the back of my lot that will power
a pond pump, 12v lighting, and occasional 120v convenience load
(radio, etc.). The entire load is intermittent, running on a timer for
a few hours a day; a full charge will give me about 20 hours of use
without the PV connected.  I'm using a 20watt panel to charge a gel
cell battery via a Morningstar Sunwise controller.. Everything is
properly fused, and the panel is mounted on a fence about 20' from the
box containing the battery/inverter setup.

Here's my question: where and how should I ground this system? I've
read lots of conflicting advice but the consensus seems to be for a
ground on th DC side at the panel (particularly for roof-installed
setups, which mine is not) and a second ground on the AC side of the
system.  That's what I'm more puzzled about, since I'm not sure how to
go about grounding it there.

One suggestion I got was to drive a ground stake next to the box and
connect a GFCI outlet to the inverter output and the ground stake.
Does that seem a reasonable way to protect users from circuit faults
on the AC side?

Thanks,

Kiwanda

  I, personally, would not ground the 12v side at all. Most electrical
codes cover less than 24 volt wiring (security systems etc..) with
lots of forgiveness and sloppiness. The 120vac side should be gorunded
and required if the GFCI is to ever function. Many places promote
grounding plates to raise the floor or concrete slab to the same
potential as the supply neutral. These are metal plates about 1 foot
by 2 feet and get embedded into the concrete floor slab or other wet
area where humans walk.

 wrote:

Thanks for the feedback.  I should note that this will be an outdoor
installation, not connected to or near any building, and seasonal in
that I'll put it all in storage for the long Minnesota winters. So a
ground stake on the AC side may be the best option.

thanks,

Kiwanda

 

A lot depends on your exact equipment and the codes/standards that apply for
your location.

PV modules with metalic frames will have a designated grounding point and should
be grounded.

If you are in the USA, see the requirements in Article 690 of the National
Electrical Code, whatever version has been
adopted by the authorities for your area.

General practice is to ground the battery negative.  Ungrounded low voltage dc
systems are allowed, but then there is
the requirement that all ungrounded conductors be provided with overcurrent
protection (generaly the use of 2-pole DC
rated circuit breakers.

Many of the low cost inverters will be damaged if the neutral is grounded while
the battery is grounded.  These are
usually identified as not being suitable for connections to buildings.

PV systems on residences require a dc ground fault on the PV array.  This is not
the usual AC ground fault protector,
but rather a function of a grid connected inverter (not likely with your power
level), or the use of special multipole
circuit breakers wherein on pole is 1 amp and can trip the other poles if
leakage within the PV array and wiring exceeds
1 amp.  Xantrex and others sell these.

All grounds should be bonded together.

A good free reference is

SAND 2005-0342-N
Revised January 2007
Photovoltaic Power Systems
And the
2005 National Electrical Code:
Suggested Practices
John Wiles
Southwest Technology Development Institute
New Mexico State University
PO Box 30001, MSC 3 SOLAR
Corner of Research Drive and Sam Steel Way
Las Cruces, NM 88003

See
http://www.nmsu.edu/~tdi/Photovoltaics/Codes-Stds/PVnecSugPract.html



Bill Kaszeta
Photovoltaic Resources Int'l
Tempe  Arizona  USA
bill@pvri-removethis.biz

 On Jun 20, 10:00 pm, wkasz...@cox.net (Bill Kaszeta / Photovoltaic
Resources) wrote:


your location.

should be grounded.

The one I'm using is aluminum but has no designated grounding point.


Electrical Code, whatever version has been

I've read a couple of articles by John Wiles on this, which heavily
cite 690. My problem is that most of the sources I've read say things
like "some people ground, some do not" rather than giving a clear
answer. The NEC isn't particularly clear on this, since it's just a
12v system and is not tied to a structure. So what I gather is that I
*should* ground it, but how remains a question.


systems are allowed, but then there is

protection (generaly the use of 2-pole DC

I've got a 5A fuse inline between the panel and charge controller, and
a 15A between the battery and inverter. Of course the inverter itself
is fused as well. I think the real justification for grounding the DC
side is static accumulation and lightning. That said, the panel will
be mounted about 6' off the ground and is surrounded by very large
trees.


while the battery is grounded.  These are

That's what I'm wondering about...the inverter I'm using is a cheap
square wave 1000 watt unit that has no ground connection lug (nor any
mention in its documentation). I could get another, but since I had a
couple of these on hand it and they met my load requirements it seemed
reasonable to use one.

[snip]

Thanks Bill-- I looked at this and a couple of similar articles but am
still not certain of best practice for this case. I appreciate your
advice though!

best,

kiwanda