[RE-wrenches] GFP and multiple charge controllers

Wed Apr 18 19:54:43 PDT 2012

Darryl, OutBack makes GFDI in single, double and quad pole flavors:  80 Amps per pole, 1/2 Amp between the ground and grounded conductor. 

The current method of ground fault protection is an imperfect beast, absolutely. However, it's been the industry standard and both the Code and standards have been written, interpreted and enforced in a manner that left installers and manufacturers little option. Like Kent, as an installer I never felt comfortable installing a device that, in a battery system, disabled the return fault current bond while leaving the inverter and DC loads operating. However, I want to call out and take exception to one of Kent's comments -- when there is a ground fault and the GF device lifts the bond, no metal object should be considered safe, no matter how securely you've grounded the array and all objects. By definition, all grounded surfaces which are normally at zero potential to ground should be considered as potentially energized when the system is indicating a fault. Think rattlesnake, loaded gun, whatever keeps your crew attentive and focused. 

I think (but have no proof) that much of what passes as unusual or inexplicable behavior with PV arrays and ground faults resides in first-fault failures in the grounded conductors of PV arrays, to which current GFDI methods are blind. 

I think the real solution will be when we as an industry transition to a more advanced method of GFDI, similar to what Europe does and what Bill Brooks and others are advocating. It's a better way. 

Phil

On Apr 18, 2012, at 4:41 PM, Darryl Thayer <daryl_solar at yahoo.com> wrote:

> Bob do you know of a 4x80 GFDI breaker?  Midnight has a 2X80 correct? and Outback has a 2X80   
> Wire size use the tap rule, 10 feet 10% of wire size.  
> 
> From: "boB at midnitesolar.com" <boB at midnitesolar.com>
> To: RE-wrenches <re-wrenches at lists.re-wrenches.org> 
> Sent: Wednesday, April 18, 2012 5:08 PM
> Subject: Re: [RE-wrenches] GFP and multiple charge controllers
> 
> 
> A lot of good replies have come by here but here goes another one...
> 
> The GFP cannot be used for dual purpose as a disconnect for battery
> or PV input and you are not allowed to un-ground the system by turning
> off the DC input or output breaker.
> 
> 4 AWG should be fine for 80 amps. If you need/want to use smaller wire
> than that required for an 80 amp GFP, MidNite makes a 63 amp GFP.
> 
> boB
> 
> 
> 
> 
> 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
>>> 
>>> 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 
>>>> Office: 907/457-1297
>>> _________
>> Voice :805-438-5600
>> email: william at millersolar.com
>> http://millersolar.com
>> License No. C-10-773985
> 
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