[RE-wrenches] GFP and multiple charge controllers

[Kent Osterberg]

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
>>> nathan at arcticsun-llc.com <mailto:nathan at arcticsun-llc.com>
>>> Office: 907/457-1297
>>
> Miller Solar
> Voice :805-438-5600
> email: william at millersolar.com
> http://millersolar.com
> <http://millersolar.com/>License No. C-10-773985
>
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