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Why is there a Neutral in my PV Combiner Box?

D90Don

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Joined
Dec 22, 2023
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24
Location
Cave Junction
I currently have a 24v Outback MPPT Controller with FLA battery bank, and I am upgrading to a 48v Victron RS450/100 Controller with SOK 48v Battery Bank Rack. Every "how to" video I have seen only has a positive and negative connection from PV array to the Victron Controller. I have not seen any combiner boxes with a neutral that is bonded to the ground in a PV Combiner Box. I have two questions, can Iegally disconnect the neutral in the combiner box, put a wire nut on it, and leave it? Second, on the sub/aux panel that joins the PV array wiring to the Outback Controller, again we have (4) wires, versus just a positive and a negative. The breakers do not appear to be DC in this box? I purchased the property with this system on it, and I am unsure of the logic behind it. Any thoughts or recommendations on how best to proceed with wiring the Victron Controller and safely dealing with this neutral? Thank you.
 

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The QO breaker box, they are DC rated up to some voltage, Tim knows the number.
Looks like they are using it as a disconnect from the combined PV over to the SCC, but it is hard to see.
The left breaker is for the battery output, the right breaker is for the PV input. I think.

The white wires appear to be a common negative for the PV and SCC.

The 4 wires into the solar charge controller are:
PV + (red)
PV -
+24 V out
0 V out

With PV - tied to 0 V out.
I believe the Victrons also bond PV - to 0V output internally, so you should not have to change any wiring. EDIT: See Next Post
Let see what other sharper eyes can see, thanks for the photos, that makes it so much easier.
 
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Ok, one of the great features of the Victron RS450/100 Controller is galvanic isolation from PV and battery.

So bonding every negative together in the QO breaker box is not good because that defeats the galvanic isolation.

Separate the wires on the - busbar in the QO breaker box so independent negatives go into the RS450/100.
The one from the top is PV -, send that wire directly to the RS450/100
The one from the bottom is Battery -, send that wire directly to the RS450/100.
Don't use the - bar in the QO breaker box at all.
 
@ricardocello , Thanks for the reply on the holiday. Happy Thanksgiving! Yes, the smaller gauge wires are for the surge protector. I'm not feeling very smart regarding the white tape on the negative. Not sure why it was done. It definitely threw me off. I'm curious if I need to change up the breakers as well in the other panel to DC specific breakers. I will have to put the current PV array all in a single circuit to bump up the voltage due to the fact the Victron needs 120v for startup and change the DC breakers to a higher rating. The Victron Controller can handle significantly higher current than the 24v Outback unit. Thank you especially on the guidance on the QO Box!
 
@ricardocello , Thanks for the reply on the holiday. Happy Thanksgiving! Yes, the smaller gauge wires are for the surge protector. I'm not feeling very smart regarding the white tape on the negative. Not sure why it was done. It definitely threw me off. I'm curious if I need to change up the breakers as well in the other panel to DC specific breakers. I will have to put the current PV array all in a single circuit to bump up the voltage due to the fact the Victron needs 120v for startup and change the DC breakers to a higher rating. The Victron Controller can handle significantly higher current than the 24v Outback unit. Thank you especially on the guidance on the QO Box!
Happy Thanksgiving! Just sitting here digesting food. Slowly.

You cannot use those QO breakers for the higher voltage, your intuition is correct.
Also, those CBI PV breakers are only rated for 150 VDC.
Honestly, there isn't much of this worth keeping if you are going to 48V and an RS450/100 (sorry), other than the combiner box itself.

If you let us know what panels you have/plan to have, people here love telling you whether it will work well.
For the 450/100, you probably want to get into the 300V+ range for optimum efficiency.

The white tape is because at some point in time the code said to use white for negative to indicate that it was bonded to ground or something.
Everyone knows red is + and black is - in DC circuits by convention.
Whoever installed it was attempting to satisfy code or inspections.
Someone with a long history in solar here will probably correct me on this.
 
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@ricardocello , thanks for passing on the "reasoning" behind the white tape. I was told a very reputable contractor installed it, so I figured there had to be a reason. I was hoping to use the Combiner Box at the PV Array and just swap out breakers for a higher current DC breaker. Then at the QO Box, I was planning on eliminating that. use the box above as a junction box and tie red and black 10 AWG wires together with wire nuts in the above junction box, and run that to the Victron RS450/100 Controller with a PV Quick Disconnect either next to the Controller or next to the junction box. I was hoping the new breakers at the PV Combiner Box would be sufficient and just the PV Quick Disconnect Switch at the Controller would be sufficient safety; but I'm up for suggestions. The green ground in the QO box, I guess I could run to the Main Load Panel/Breaker Box.
 
Currently it is 6 panels of 240 Watts wired up 3 panel in series x 2 to each DC breaker. I'm measuring 90 volts input at the current Outback Controller. I need to bump that up to at least 120v so I plan on putting all 6 panels in series, until I rent a scissor lift to replace the current array. I want to get the new "system" up and running (less panels) prior to replacing the 240W panels, since the current Outback Controller cannot handle any additional PV capacity. I have 400 Watt panels sitting in the crate, but one step at a time.
 
Currently it is 6 panels of 240 Watts wired up 3 panel in series x 2 to each DC breaker. I'm measuring 90 volts input at the current Outback Controller. I need to bump that up to at least 120v so I plan on putting all 6 panels in series, until I rent a scissor lift to replace the current array. I want to get the new "system" up and running (less panels) prior to replacing the 240W panels, since the current Outback Controller cannot handle any additional PV capacity. I have 400 Watt panels sitting in the crate, but one step at a time.
What’s the maximum voltage input on your charge controller? I’m using 3 in series and that’s the sweet spot for my equipment.

Never mind. I went back and looked at your original post. You have a 450 volt CC. I’m limited to 150.
 
@ricardocello , Thank you for clarifying and the link! The Victron min startup voltage is 120vdc. But the system is much higher than 125vdc. So I will eliminate that load center. Regarding the DC breakers that I currently have and need to replace/upgrade, are DC Breakers standard size or do they vary by manufacturer/ are they proprietary like AC Breakers? or stated differently, do different combiner box manufacturers have their own specific dc breakers?
 
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The system could be negative grounded. I believe that was best practice or mandatory at one point, and an old school installer may have kept designing that way even after most people moved to ungrounded PV.

The white negative looks isolated in these boxes but idk where the standard bonding location was for that.
 
@ricardocello , Thank you for clarifying and the link! The Victron min startup voltage is 120vdc. But the system is much higher than 125vdc. So I will eliminate that load center. Regarding the DC breakers that I currently have and need to replace/upgrade, are DC Breakers standard size or do they vary by manufacturer/ are they proprietary like AC Breakers? or stated differently, do different combiner box manufacturers have their own specific dc breakers?
Try these DIN rail breakers, should fit the box, but check the height and length:
MNEPVxx-600-2PP

DIN rail is somewhat standard, the box around them may or may not have room for the bigger ones.
 

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