Phil,
While using a dual GFDI to open both positive and negative array
conductors is the safest thing to do in battery systems, and it is
clearly compliant with 690.5 to do so, it is not consistent with the
manufacturer's instructions or the device listing. So that leads back to
a violation of 110.3(B). I find the present situation very disturbing.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
t: 541-568-4882
On 4/18/2012 8:28 PM, Philip wrote:
Hi Kent,
I wanted to add a little more re positive grounding. OutBack's
communication structure, like many other manufacturers, is referenced
to Negative. If you install multiple devices in a positive ground
system and connect them together via a Hub and add
disconnects/overcurrent protection like normal in the ungrounded (this
time negative) conductor, any time the breaker opens current will try
to return to the battery by any means possible, and that means through
the comm cables. That pretty much takes out all the connected devices,
it aint pretty. Therefore, OutBack recommends using double pole
breakers, in both positive and negative conductors, when using
multiple connected current-generation devices in positive grounded
systems. Not a perfect solution, but it is what it is.
To answer your question about upgrading older systems, if I were
working on my mother's house and I had the option, I would not install
any of the current generation GFDI devices. That might be heresy and
not technically Code compliant, but on a battery based system I
believe it to be the safer option. If I had to install one, it could
go on either the battery or the array side of the controller. Once
there is a better solution I would go back and retrofit Mom's system,
because it's worth it.
BTW, OutBack's double and quad GFDI can be used to simultaneously
disconnect both positive and negative, per your desire. That's another
advantage of a multi-pole device.
Phil
On Apr 18, 2012, at 2:21 PM, Kent Osterberg <k...@coveoregon.com
<mailto:k...@coveoregon.com>> wrote:
William,
Square D used to make a QO breaker body without the overcurrent trip
mechanism. Internally it just had the switch contacts and it was
intended for use as a disconnect in locations where overcurrent
protection was already provided. The reason I mention this is that
the 80-amp PV GFP should not be thought of as overcurrent protection.
In fact it would be most appropriate if the 80-amp side of the GFP
didn't have an overcurrent trip mechanism. It /should/ only be
sensitive to ground faults. If it is sensitive to overcurrent, then
it may be activated when there isn't a ground fault and unnecessarily
disconnect the negative conductor from ground.
Code prohibits the use of a GFP as a disconnect for the PV array. I
believe that's because they intend the power system to remain bonded
to ground except in the event of ground fault. It follows that the
GFP should not be used as a disconnect between the batteries and
charge controller either. That's my interpretation. The Code doesn't
mention the possibility of putting the GFP between the batteries and
charge controller as Outback's instructions for the GFDI require. So,
even though Outback's instructions for the GFDI don't show it, put an
appropriate breaker for overcurrent protection between the battery
and the GFDI, then use wire that's appropriate for the charge
controller and overcurrent protection.
In my opinion putting the GFDI between the batteries and charge
controller is a really bad idea. Nearly all charge controllers warn
that the battery should be turned on first and turned off last. It
puts much more stress on the charge controller when the battery
circuit is opened under load than it does when the PV circuit is
opened. In fact opening the battery circuit may well cause the charge
controller to fail. Outback warns that if their charge controllers
are connected to a positive ground system, the communication port of
the charge controller or the Hub may be damaged. If there is a fault
in the PV array that causes the GFDI to open, it very well may leave
the system in a positive ground condition.
When upgrading an older PSDC Outback system which instructions are
more appropriate to follow? The ones for the PSDC that show the GFP
before the charge controller. Or the newer instructions for the GFDI
that show it after the charge controller. Except the the label and
instructions the GFP and the GFDI are identical. In case you don't
remember, the PSDC came with a schematic showing all possible options
attached to the back of the front panel. When it comes time to
troubleshoot sometime in the future, that schematic is still going to
be there.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
t: 541-568-4882
On 4/17/2012 6:42 PM, William Miller wrote:
Friends:
Here is a related problem: If we use an 80 amp GFD (ground fault
detection) breaker, even for a very small array, we have to use 3AWG
CU wire from the battery buss to the breaker and from the breaker to
the FM or MX60. This seems like a big hassle for 5 or 10 amps of
charging. A variety of sizes of GFD breakers would be helpful.
Here is a bigger problem: GFD breakers don't really work. All they
do is turn off the charge function in hopes that someone will find
the problem. In the meantime, the negative-to-ground bond is
removed and module mounting framework could be energized. PV GFD
breakers are completely different from standard AC GFDI (ground
fault detection and interruption) receptacles and circuit breakers.
The AC versions interrupt power upstream, the PV versions interrupt
power /downstream/ from the fault.
See:
http://millersolar.com/MillerSolar/case_studies/ground_fauilt/_ground_fault.html
for some musings on the subject.
As they say on TV: "There had to be a better way!"
William Miller
At 05:54 PM 4/17/2012, Kent Osterberg wrote:
Nathan,
I don't think anyone makes a 100-amp PV GFP. The panel mount
breaker model that's being used for the PV GFP doesn't include a
100-amp breaker.
The Classic has a built-in GFP so you shouldn't need an external
GFP for it. You will need to add a GFP for the FM60 - a single
80-amp GFP would work.
You can use the dual 80-amp GFP and shut down both PV arrays at the
same time if the GFP is wired to disconnect the PV array from the
charge controller input. That's where Outback's instructions used
to show the GFP, and it is a better place for it than on the charge
controller output anyway. Midnite's instructions show the GFP on
the charge controller input, but their 80-amp GFP is a single.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com <http://www.bluemountainsolar.com>
On 4/17/2012 11:08 AM, Nathan Stumpff wrote:
Wrenches,
In a job coming up I have a customer with an existing FM60
controller, 520 watt (!!) array. We are doing a ton of work,
including adding a 4 kW solar array with Classic 150 charge
controller. I am trying to figure out how to handle the GFP.
For the Classic, I need a 90 or 100 A output breaker minimum. 80 A
is not an option. The OutBack dual GFP is 80 A, and so it not an
option.
Is there a 100 A GFP breaker assembly I have just never seen? Is
there a way to use the Classic's GFP to run an external relay via
AUX (to trip the FM60 output breaker at the same time)? Any ideas?
Thanks,
-Nathan
--
Nathan J. Stumpff - Arctic Sun, LLC
NABCEP Ceritified PV Installer #091209-175
nat...@arcticsun-llc.com <mailto:nat...@arcticsun-llc.com>
Office: 907/457-1297
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