why have two circuit breakers in series?

[vtmaps]

I have been studying the wiring diagrams for the E-panel.  I notice that the output from the combiner box goes through a 60 amp and a 63 amp breaker on its way to the PV+ input of the charge controller. 

I realize that the 63 amp breaker is ganged to a 0.5 amp breaker (for ground fault), but I don't understand why two breakers (60 and 63 amp) are in series.  Can you explain this?

thanks, vtMaps

[Halfcrazy]

When using a Charge controller that does not have GFP built in (The Classic has GFP in it by the way) you need to use an external GFP breaker this assembly is a ganged .5 amp and a 63 amp breaker. When the .5 amp breaker trips do to the ground fault it will open the 63 amp disconnecting the charger to meet code. I think the best way is to think of the 63 amp and .5 amp as a ground fault protection device it is not an over current device for the incoming pv line. This also can NOT be used for a pv disconnect because opening it will break the earth ground reference to battery negative.

[vtmaps]

This also can NOT be used for a pv disconnect because opening it will break the earth ground reference to battery negative.

That hadn't occurred to me.  What is so bad about breaking the earth ground reference (when the panels are also disconnected)?  When a ground fault trips the 0.5 A breaker, wouldn't the earth ground reference also be broken?

--vtMaps

[mike90045]

This also can NOT be used for a pv disconnect because opening it will break the earth ground reference to battery negative.

That hadn't occurred to me.  What is so bad about breaking the earth ground reference (when the panels are also disconnected)?  When a ground fault trips the 0.5 A breaker, wouldn't the earth ground reference also be broken?

--vtMaps

That's the NEC for ya !  99% is good, but then .....    I'm waiting to see if the all the Arc Fault Breakers and all the required GFI stuff, will trip the XW6048 offline.....

[Halfcrazy]

This also can NOT be used for a pv disconnect because opening it will break the earth ground reference to battery negative.

That hadn't occurred to me.  What is so bad about breaking the earth ground reference (when the panels are also disconnected)?  When a ground fault trips the 0.5 A breaker, wouldn't the earth ground reference also be broken?

--vtMaps

The danger here is that if there is no reference to ground on the negative it floats. This in its self is no issue but take a guy that assumes negative is ok to touch and they find pv negative floating at 200volts compared to earth ground. This is going to hurt.

As for the bond when there is a GFP this is a deathtrap and the NEC in my opinion is going to get someone killed with this foolish setup you will never find a functional GFP on any of my installs. I always explain the dangers of GFP to my customers and let them make there own decision. When GFP is used in a system the DC negatives should be considered a current carrying Hot conductor and be breakered and treated as such. Of course this is just my opinion and MidNite Solar in no way endorses ignoring the NEC 

[vtmaps]

As for the bond when there is a GFP this is a deathtrap and the NEC in my opinion is going to get someone killed with this foolish setup you will never find a functional GFP on any of my installs. I always explain the dangers of GFP to my customers and let them make there own decision. When GFP is used in a system the DC negatives should be considered a current carrying Hot conductor and be breakered and treated as such. Of course this is just my opinion and MidNite Solar in no way endorses ignoring the NEC

Interesting.  My off-grid system includes a stretched E-panel with outback vfx3524 and flexmax60.  The flexmax60 is a few inches (of conduit) away from the E-panel.  My system (about 18 months old) was (supposed to be) installed to code, but I have only the GFP (63 A breaker ganged to the 0.5 A breaker) for a PV disconnect.  I always assumed that my PV disconnect was out at my mnpv6 combiner box.

My reason for starting this thread is that I would like to do some system upgrades (myself) and I am studying wire diagrams, and noticed the discrepancy between my system and the E-panel wiring diagram.

I think my very first upgrade will be to install some sort of battery disconnect outside of the E-panel.  The reason for this is that I want the E-panel completely dead when I work on it.  Working on the E-panel, with its extensive unfused battery bus, is too scary for me.

After a battery disconnect, my next upgrade (based on what I've learned in this thread) will be to install the missing 60 A breaker.  Would it be OK to install it BETWEEN my flexmax and my E-panel?  That way, I could save myself a trip to the combiner box when I want to remove all power from the E-panel.

While I have your attention, perhaps you could give me the NEC view on battery disconnects.  I would like to disconnect my battery box from the E-panel with the flick of a switch.  I am looking at an inexpensive 300 Amp DC switch by Blue Sea.  Will that meet code?  Should I use a breaker instead of a switch? Also, can I mount the switch (or breaker box) on my (home made plywood) battery box, or must I interrupt the conduit between the battery box and the E-panel for the disconnect.

--vtmaps

[Robin]

If you want a disconnect between the batteries and the E-Panel, a Blue Sea will work electrically, but it won't meet code. The Blue Sea is made for boats, right? It is not capable of attaching conduit to it. You are not allowed to have exposed cable in an NEC compliant system. The battery disconnect must also be listed for the intended use. If you can keep the battery cables from being exposed and if the Blue Sea is listed tor ULq741, then you are good to go. If not, then the next choice will probably be our MNDC. It is fairly inexpensive.
You can mount your 60 or 63 amp disconnect inside the E-Panel. That is the most common place. You could just disconnect the .5 amp portion of the DC-GFP. Hardwire the battery negative to earth ground. That would give you a disconnect that does not disconnect earth ground when turned off. That will not meet code, but then your FM60 doesn't have an arc fault protector in it either, so regardless, you will not meet code with this setup. If your system is not going to be inspected, don't worry about the Dc-GFP. There has never been a case that I am aware of where a DC-GFP has stopped a fire from happening. Arc fault protectors do actually work though.

[vtmaps]

Thanks for all the comments, I am getting quite an education here.  I have just been studying the Outback wiring diagrams.  I notice that they put their GFP between the charge controller and the positive battery bus.  It is not between the Array and the charge controller.  They write: 

The OutBack Power Systems' Ground Fault Detector Interrupter (GFDI) is a safety device for a photovoltaic (PV) array. In the event that the array becomes shorted to ground, it disconnects the PV system from the batteries.

Why the difference?  Does it matter which location the GFP is in?  They do seem to understand the danger of a tripped GFP device as evidenced by the following label:

WARNING!  ELECTRIC SHOCK HAZARD IF A GROUND FAULT IS INDICATED, NORMALLY GROUNDED CONDUCTORS MAY BE UNGROUNDED AND ENERGIZED

--vtMaps

[boB]

Thanks for all the comments, I am getting quite an education here.  I have just been studying the Outback wiring diagrams.  I notice that they put their GFP between the charge controller and the positive battery bus.  It is not between the Array and the charge controller.  They write: 

The OutBack Power Systems' Ground Fault Detector Interrupter (GFDI) is a safety device for a photovoltaic (PV) array. In the event that the array becomes shorted to ground, it disconnects the PV system from the batteries.

Why the difference?  Does it matter which location the GFP is in?  They do seem to understand the danger of a tripped GFP device as evidenced by the following label:

WARNING!  ELECTRIC SHOCK HAZARD IF A GROUND FAULT IS INDICATED, NORMALLY GROUNDED CONDUCTORS MAY BE UNGROUNDED AND ENERGIZED

--vtMaps

The GFP is supposed to connect and disconnect between the PV input to the charge controller from the PV positive, not the battery.
Which wiring diagram are you referring to ??

Yeah, the GFP is supposed to fix fire related problems, not shock hazards...  It kinda trades one for the other.

The warning message is the proper NEC way of protecting from shock hazards.
Don't you feel safer and more comfortable now ?

boB

[vtmaps]

Which wiring diagram are you referring to ??

I can't figure out how to insert the image... go to Outback's site and look for this wiring diagram:
"Ground_Fault_Detector_Interrupter_REV_A.pdf"
--vtMaps

[boB]

Which wiring diagram are you referring to ??

I can't figure out how to insert the image... go to Outback's site and look for this wiring diagram:
"Ground_Fault_Detector_Interrupter_REV_A.pdf"
--vtMaps

If you google for   "Ground_Fault_Detector_Interrupter_REV_A.pdf", it comes up as an OutBack drawing as far as I can tell...
And it certainly does appear to have the battery positive connected to the GFDI/GFP. 
Strange...

I looked at our (MidNite) drawings and didn't see any connected to the battery side, although looking at a couple of the drawings, and the stackup of breakers in the picture, I can see how one might wonder if it is also connected to battery plus.


boB

[vtmaps]

If you google for   "Ground_Fault_Detector_Interrupter_REV_A.pdf", it comes up as an OutBack drawing as far as I can tell...

I didn't find it through google.  I found it directly on Outback's site.

And it certainly does appear to have the battery positive connected to the GFDI/GFP. 
Strange...

I looked at our (MidNite) drawings and didn't see any connected to the battery side, although looking at a couple of the drawings, and the stackup of breakers in the picture, I can see how one might wonder if it is also connected to battery plus.

I didn't see any of your (MidNite) drawings where the GFP appeared to be connected to the battery plus.  This whole discussion is giving me a headache... but that is a small price to pay if I can avoid burning my place down or electrocuting myself or others.
--vtMaps

[boB]

I didn't see any of your (MidNite) drawings where the GFP appeared to be connected to the battery plus.  This whole discussion is giving me a headache... but that is a small price to pay if I can avoid burning my place down or electrocuting myself or others.
--vtMaps

Disconnecting on the battery side should work as well as disconnecting from the PV side.  So it shouldn't matter.
Any way to stop the PV current, unless maybe if the controller itself has the short instead of the wiring.

Not sure why or when OB made that change but it should be OK.
boB