William,
There have been too many fires where GFP failed to operate correctly to
argue that they are really good at what they are supposed to do. But, I
think it is inappropriate to say they don't really work at all. How many
fires could have or would have happened without the GFP devices? Does
anyone have stats?
In every PV system I've installed, and since you do high quality work,
I'm confident that in every one that you have installed, the mounting
framework is securely grounded. The GFP device does not change that
circumstance. Every junction box, conduit, mounting rail, and PV module
is grounded and safe to touch regardless of what the GFP does. If
someone removes /the /module grounding while looking for a ground fault,
then it is possible to have an energized module frame, but the GFP
didn't create this risk. The system could be solidly grounded with no
GFP device and the module frame would be just as energized. It's
important that every PV installer understand that risk and also
understand that every properly grounded component of the system is still
perfectly safe.
My major complaint about the GFP is that, in battery systems, they
expose the homeowner to unsafe conditions. 690.5(C) requires that a GFP
hazard warning be located within site of the batteries. Unfortunately,
the person servicing the 12-volt or 24-volt refrigerator or lights isn't
going to see that warning. In the event of a ground fault that opens the
GFP device, the negative wire going to the lights or refrigerator or any
other dc load may be energized to -150-volts to ground. Or maybe -300
volts or -600 volts with some of the new charge controllers. Ground, the
green wire running everywhere, is connected to the positive PV wire
someplace in the array and the negative wire is connected to every
negative wire in the system. If the unexpected voltage isn't a bad
enough risk, the current may be worse. There is nothing to stop the arc
from the shorted PV array if someone accidently connects negative to
ground. This is actually a preventable circumstance: the GFP simply
needs to open both PV+ and PV-. The manufacturers need to step up and
correct this. The NEC needs to be changed to require it. This won't
reduce the risks at the PV array, but it is certainly worth it to design
components that don't but homeowners at unnecessary risk.
Kent Osterberg
Blue Mountain Solar, Inc.
www.bluemountainsolar.com
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
Miller Solar
Voice :805-438-5600
email: will...@millersolar.com
http://millersolar.com
<http://millersolar.com/>License No. C-10-773985
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