PV GFP

Re: PV GFP

As I understand, you connect the 80 amp (or 63 amp) DC GFI breaker between the PV Array + and then through a another appropriately sized breaker, then to the PV + array input to the charge controller... Not between the battery bank and the charge controller.

Note that the DC GFI breaker is not really used to trip on the current. It is a "slaved switch" (two breakers are "ganged together" to a second ~1/2 to 1 amp breaker. That second current flow detection breaker is connected between the battery negative bus and the "earth ground". If there is a "ground fault" in the system that causes current to flow between the Battery negative and earth ground, the small breaker trips, which then turns off the "main breaker".

The second breaker in series with the DC GFI Breaker on the PV array is actually the over current protection/ On-Off switch for the array. You don't want to use the DC GFI to turn on/off the array as this also would disconnect the safety ground too--potentially making the system unsafe (floating battery bus ground).

You would connect a second breaker (again, appropriate size) between the Charge Controller and the Battery Bank. This breaker would be a single pole breaker with no DC GFI function.

These breakers are available with "non-standard" rating/markings (as I understand). Normally, you would define the maximum continuous current (say 60 amps). Multiply that by 1.25 for the NEC safety factor or 60*1.25=75 amps minimum. And then round up to the next standard wire and breaker rating. I believe that Outback started by offering a "63 amp" breaker for use on a 60 amp charge controller. But the wiring should still be rated for >75 amps (as an example).

Our host, Northern Arizona Wind & Sun does have 63 amp and 80 amp versions. From my point of view, the 50/63/80 amp DC GFI breaker just has to be greater than 1.25*Imp-array--otherwise its current rating does not matter--It is "just a switch". The smaller breaker (~1/2 to 5 amps) is what sets the "sensitivity" to earth fault current.

Note: I have a big problem with DC GFI Breakers and think they are unsafe to use in a "typical" off grid solar power system--regardless of what the NEC says. Normally, you would never ever put a fuse or breaker in the main system DC safety ground.

If you want to read the details "why" I believe this... Here is a discussion on the Midnite Forum:

Ground Fault Protection

The summary is that a solid DC Battery Bus ground to green wire safety ground (cold water pipes, ground rod driven into soil, connection to AC main ground, etc.), is usually much safer (for many reasons) than adding a DC GFI assembly because of the lifted ground (the DC GFI is intended to reduce the risk of arc faults between PV + and earth ground--But ARC Fault Breakers/circuitry does a much better job of this--in general--but there are still lots of details that affect final wiring choices). There is no "good/simple" answer here.

-Bill

Re: PV GFP

Hmm... I see what you mean (PDF download).

There are many reasons, in my humble opinion, why this is both unsafe and makes a single point of failure takes out multiple/all charge controllers--assuming that any single breaker in the "pack" turns off all breakers (and lifts safety ground except for a 43 kOhm resistor across the sense breaker--for static discharge I believe).

From a ground fault control--It should not make any difference if the DC GFI is in front of, or behind, the charge controller (unless they controller is being protected against Hot to Earth ground faults too). Nominally, the whole DC GFI was to protect wiring failures (hot to earth fault) in the solar array wiring (as I understand).

I would not do it. (that opinion and $5 will get you a cup of coffee:roll:).

Regarding the continuous duty breaker rating--I am not sure what they did this--and if the breaker is simply a "re-marked" 80 amp breaker or if there is a real difference (internally) with a 63-64 amp continuous rated breaker and a standard NEC 80 amp breaker.

In any case, from what little I understand, even with a "63 amp continuous rated" breaker you would want 80 amp rated wiring and for an "80 amp continuous rated breaker" you would want 100 amp minimum rated wiring.

Regarding an 80 amp breaker on a 60 amp output (or input) solar charge controller... Remember that breakers are there to protect the wiring, not the device. So, you can have a larger rated circuit breaker and wiring without any problem (there is usually a maximum input rating to any electrical device--i.e., you cannot put a 1,000 amp breaker on a 100 amp maximum input circuit charge controller as this would be in-excess of the maximum design input current rating for the device--It can be hard to find this "not to exceed rating" for many devices).

Normal NEC rated breakers are designed to never trip at 80% of rated current, and should always trip at 100%+ of rated current (that may take minutes to hours to trip at 100% of rated current). Between 80-100% of rated current is the "false trip" zone and you don't want to be operating there under normal conditions.

-Bill

Re: PV GFP

And when done the Outback way--Turning off the power to allow servicing of the charge controllers also lifts the safety ground too (as well as turns off all parallel charge controllers).

I would suggest that each charge controller should have its own circuit breaker for servicing.

And, in past NEC regulations, you are not ever supposed to use the DC GFI switch for "on/off" branch circuit control as this lifts the DC Safety Ground... And why you see the Midnite documents show both a DC GFI and a normal circuit breaker in series.

In any case, the present DC GFI causes why more issues than it solves (and in reality, doing a fault analysis shows that the 1/2 amp circuit breaker is doing the Arc Fault suppression, it is not the "main breaker"--Which is totally counter to good engineering safety design which is 100% against ever lifting the safety/green wire ground--Why they require separate ground connections, double nutting, welded/swagged permanent splices for safety grounds, etc.).

-Bill

Re: PV GFP

For many folks, they have to go through a building department/inspector--It may not be so easy to "ignore" the DC GFI for those folks.

Again, this is just my personal opinion--If you have any further questions/concerns, please ask. Not trying to "bully" anyone into seeing my position.

If you are very concerned about solar array related fires and how to address the issues--The new "Midnite" combiner boxes with a "bird house" emergency array shutdown box is an interesting solution. Add that Midnite Classic controllers have Arc Fault detection/shut down, I would suggest that these are a much better solution (although, you are going to pay a lot of money for these features--I would guess).

Running as much of the exposed wiring in metal conduit (if you have little nibbling roof top/array residing creatures) is going to address many of those issues. And making sure your electrical connections are done correctly (no "series arcs") will help too.

DC GFI (stopping DC Hot to Earth ground arc faults) is not any related to the AC GFI we are all used to (that reduces the chances of electrocution from a user standing in water, etc.).

There are also AC Arc Fault breakers for homes these days--They can be a bit of a pain. A few people here have said that their vacuum cleaner can trip those Arc Fault Breakers (the Universal/Brushed Motor is full of "arcs" at the commutator).

Sincerely,
-Bill

Re: PV GFP

Would be "interesting"... But there is nothing (that I am aware of) that is available today to perform this function. And I still don't like the momentary lifting of ground (switched ground). All it takes is a near by lightning hit to mess up the system grounding.

I believe that somebody had an idea how this DC GFI could be made with existing "Listed" components (circuit breakers) to perform this function (or use Listed Fuses for electronic shutdown of some charge controllers).

I think it has created more problems than a DC GFI (as implemented) could ever solve.

-Bill