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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