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Combiner Box Help

cdsolar said:
Yes, that 600V breaker, if indeed it is the one below, is only rated for 600V if it has the clip joining the two halves that connects at the bottom between the positive and negative. Yes it is confusing at first. So it is really a single pole at 600V wired between two breakers that are ganged. Here is the image. Note the copper clip in the left-hand image:

Product - MidNite Solar

MidNite Solar Product Page.
www.midnitesolar.com

If you remove the copper clip, then it is just two 300V breakers ganged together. I use this very breaker without the clip as a 2-pole 300V disconnect (required by NEC) for both + and - PV.
Click to expand...
Yes, Midnites diagram doesn't show it but it's a 600V array on the left and 300V on the right, note the "Operation "up to" 600V.

MNEPV20-600v-Wiring-v2 (1).png
 
Brucey said:
Right, it's two 300V breakers, it's only good for 600V when you are running it in series.

Basically in the configuration you have wired with the positive and negative of a string coming in to each pole, there's 300V of protection for each.

View attachment 212720
View attachment 212721
Click to expand...
I spoke with Scott in tech support at Midnite Solar. Just as I said. Their breaker is tested to UL489 and provides 600 volts of DC protection on the PV+ and PV- poles. What you were looking at was a different testing and concluded the protection was only 300 volts. They sell a 150 VDC, 300VDC and 600VDC breaker. Choose accordingly.
 
Brucey said:
Yes, Midnites diagram doesn't show it but it's a 600V array on the left and 300V on the right, note the "Operation "up to" 600V.

View attachment 212753
Click to expand...
Option 1 is incorrect. Option 2 is correct. Again, the double pole 600VDC breaker is UL489 and will protect to 600VDC. Not 300 as is being claimed by others on this thread. they are not looking at the UL489 testing which applied to this breaker. In fact, Midnite sells a 150VDC, 300VDC and 600VDC breaker.

Not to toot my own horn, but I again confirmed with Scott in tech support at Midnite solar the combiner box wiring with the fuses and double pole breaker which I posted above in the thread to be correct. That photo does not also show the Midnite solar lightening arrestor rated 600VDC which his wired to ground, PV- and PV+. The PV+ line from array is connected through a high voltage and high amperage WEGO connector and is confirmed well within spec for this application.

My final word: Use your advisors/contributors wisely, but not blindly.
 
glandpuck said:
Option 1 is incorrect. Option 2 is correct. Again, the double pole 600VDC breaker is UL489 and will protect to 600VDC. Not 300 as is being claimed by others on this thread. they are not looking at the UL489 testing which applied to this breaker. In fact, Midnite sells a 150VDC, 300VDC and 600VDC breaker.

Not to toot my own horn, but I again confirmed with Scott in tech support at Midnite solar the combiner box wiring with the fuses and double pole breaker which I posted above in the thread to be correct. That photo does not also show the Midnite solar lightening arrestor rated 600VDC which his wired to ground, PV- and PV+. The PV+ line from array is connected through a high voltage and high amperage WEGO connector and is confirmed well within spec for this application.

My final word: Use your advisors/contributors wisely, but not blindly.
Click to expand...
Here's what Shawn responded to me with, it does protect up to 600V via two 300V in series:

"These breakers are made up of 300V in series. You can wire it to
protect both PV+ and PV- and get the 600v if done a certain way.
Attached is a drawing showing the 2 ways to use the breaker. Note on
option 1, there is the jumper at the bottom of the breaker. This jumper
is a copper bus bar supplied by the factory and you will need to remove
it to wire as in option 2."

My question:

Had a quick question, are each of the poles on this breaker capable of
> 600V? Or is it two 300V breakers with a series link to achieve 600V
> combined?
>
> Reason being I'm looking for something to protect a string from an
> array of panels to my Victron rs450/100, and it's running around 400V,
> looking for disconnect as well as protection for both PV+ and pv-.
 
Thanks @Brucey for the followup. Not sure if I wrote this above or not, but I use this very breaker (30A version) as my NEC-required 2-pole PV+/PV- disconnect at the side of my barn where the ground mount wires enter, in an MNPV3 box, doing double duty as a breaker and a required disconnect. I don't need anywhere near 600V or even 300V, but it works well. (with the busbar removed).
 
Last edited:
Nobodybusiness said:
Sorry busy this weekend.

Honestly if it were me, I would get a higher voltage Charge controller and avoid all the parallel inputs.

It just makes it so much easier.

Reconfigure your array to match and be done with it.
8s2p


I realize not everyone can go buy one but your cost in wiring, breakers and combiners would cost as much or more than the Charge controller anyway.

Hope this helps..
Click to expand...
Hi sorry for the long absence. I'm finally getting around to trying to find a replacement charge controller. I have looked at the EG4 controller and Midnite Classic 250 (would have to rewire to 4s2p in this case). Any suggestions on a good controller? Panel specs are in original post. Less cost would be helpful but I also want to get something that will work well and last a while. Being able to monitor through wifi is a bonus if there is one. I am replacing our lead acid batteries with lithium - also looking at EG4's LifePower4 or LL-S batteries. Thanks again for your feedback.
 
Midnight has some (expensive) higher voltage SCC now.
 
glandpuck said:
This is how I wire a single string PV array in the combiner box, but it applies to multiple parallel strings as well. In this case, one string for up to 500 VDC.

The PV + and PV- each enter into a DIN rail mounted solar fuse holder. In this case, 20 amps. Then they exit the fuse holders and go into a double pole breaker, rated for 600 VDC and 15 amps. They exit the breaker as follows: The PV+ directed to a DC disconnect switch, one switch pole for every PV+. The PV- exits the breaker to a PV- buss bar. The lightening arrestor (Midnite Solar 600 VDC rated) is attached to the ground buss bar in the combiner box, the PV- buss bar and the PV+ wire before the PV+ is attached to the solar fuse. Leaving the combiner box is a wire from the PV- buss bar, the ground buss bar and the PV+ wire (goes to disconnect switch), then they can go to the inverter. The ground buss bar is connected to the array by bare copper wire bonded to all metal parts of the array, the rails and panels. There is also a ground earth rod too, but this is controversial on this site.

This provides protection to the inverter on the PV+ and PV- sides and 2 points of disconnecting power to the inverter, at the breaker PV+ and PV- and the switch PV+.

If doing parallel array strings, the photo of combiner box one shows lower voltage strings in this case and only the PV+ travels across a single pole breaker. The PV+ line was fused with a solar breaker using a fusible DC disconnect switch. The bottom of the breakers uses a buss bar to connect the PV+ to a single point of exit to the disconnect switch. This method is cheaper, but does not protect the PV- side of the circuit to the charge controller. The PV- does carry current too.
Click to expand...
I have a question concerning the wiring of the strings to the breakers in your combiner box. Are these breakers non-polarized? If not, they are wired backwards. I use the same box. In it are 6 breakers. Two for the string inputs. Two for the ground fault and two for the shutdown to the charge controller. All of the inputs are connected to the bottom plus terminal of the breakers because they are polarized breakers. The label on the breakers advises against wiring with reverse flow. Midnite also uses the bottom plus terminal. I am waiting for delivery of two two pole non-polarized breakers to use for the combiner box outputs (shutdown} and inside the building before the charge controller. I don't know for sure but read on this site that the outputs to the charge controller require non-polarized breakers for NEC code even though I don't understand why.20241007_153202.jpg20240928_135445.jpg
 
patrickparrott said:
I have a question concerning the wiring of the strings to the breakers in your combiner box. Are these breakers non-polarized? If not, they are wired backwards. I use the same box. In it are 6 breakers. Two for the string inputs. Two for the ground fault and two for the shutdown to the charge controller. All of the inputs are connected to the bottom plus terminal of the breakers because they are polarized breakers. The label on the breakers advises against wiring with reverse flow. Midnite also uses the bottom plus terminal. I am waiting for delivery of two two pole non-polarized breakers to use for the combiner box outputs (shutdown} and inside the building before the charge controller. I don't know for sure but read on this site that the outputs to the charge controller require non-polarized breakers for NEC code even though I don't understand why.View attachment 250626View attachment 250627
Click to expand...
Are you referring to this one? It's not intuitive but that's the correct orientation for parallel strings and the polarized breakers. Assume there's a fault in the string for breaker 1. All the available current from the other strings wants to go there. So the higher potential is coming from the combined other strings, therefore those should be on the ++ side of the breaker. But yes, there is a fire risk if you use these as disconnects under load when wired this way. Ideally they would be non polarized and then you can use them as disconnects as well.

Screenshot_20241018_070601_Chrome.jpg
 
I'm going to finish the wiring when the non-polarized breakers arrive, repost a combiner pic and continue this discussion then. That way there will be no hypotheticals. I may also call Midnite and get their input. I want to make sure that the combiner box is wired correctly. Thank you for the response.
 
I didn't reach agreement when I attempted to discuss this topic with midnight. But I dropped it when I learned a non-polarized breaker was (supposed to be) available.

I say, slide a rod through all the handles so the breakers are ganged, and then put the (+) breaker terminals to the PV panel (+) output. That should work whether there is a short at the inverter MPPT inputs or a short in a PV string.

The backwards connection shown in photo above will be OK so long as breaker is opened when SCC input is charged up to Vmp. Breaker upon opening only needs to hold off Voc - Vmp. Might not work, however, if you open it when it is looking into a short (e.g. connected backwards to inverter/scc with reverse-polarity protection diodes.)
 
If I follow that correctly,

There are two PV strings. Each has (-) go to a busbar, (+) to a 30A breaker.
Output of two 30A breakers combine and make two passes through 63A and unlabeled poles of "GFCI" system.
Output of (-) busbar goes through 30A pole of "GFCI" system (I think that may be a problem depending on Isc).
(-) busbar is wired through 0.5A breaker of "GFCI" system (if it carries current, disconnects both (+) and (-) poles.)

Surge suppressor lands on (-) busbar, (+) after two parallel 30A breakers, Ground.

What is Isc rating of each PV string? Are there just two PV strings, or does each input get fed by more than one PV string (which would not provide enough backfeed overcurrent protection)?

With 30A pole carrying combined PV(-), 30A / 1.56A (if thermal) or 30A / 1.25A = 24A sum of Isc. (if magnetic hydraulic, which I think these breakers are.)
 
There are two strings. Each Isc is 13.7A. One enters from the left and one from the right. The panels are fixed at Latitude 45 degrees so I doubt that they will ever make it to max output. The shutdown breakers are non-polarized. The string breakers are polarized. 20241007_153202.jpg20240928_135445.jpg
littleharbor2 said:
The red ferrules, red and white tape and white wire could be confusing to some.
Click to expand...

I'll cover the red ferrules with white tape and will see if I can find a couple larger ones for the #8 red output wire.
 
patrickparrott said:
There are two strings. Each Isc is 13.7A. One enters from the left and one from the right. The panels are fixed at Latitude 45 degrees so I doubt that they will ever make it to max output. The shutdown breakers are non-polarized. The string breakers are polarized.
Click to expand...

Close, then with 27.4A Isc.

Oh, there is a non-polarized 30A with (+) and (-) going through the two poles.

0.5A GFCI trips 63A pole interrupting (+)

I'd rather the disconnect was higher current than 30A.


Since two strings being paralleled, OCP isn't required.

Only issue (other than nuisance tripping) that I think of is the polarized 30A breakers. Let's say one string was somehow shorted, sinking current from the other string. Open breaker of other string and it is able to interrupt current. Open breaker of shorted string and it is carrying current in backwards direction, may not interrupt successfully.

Separate breaker poles is convenient for testing, but does appear to have this issue. Don't know if the problem has ever occurred anywhere other than my head (requires a shorted string, not just somewhat lower voltage.)
 
Hedges said:
Close, then with 27.4A Isc.

Oh, there is a non-polarized 30A with (+) and (-) going through the two poles.

0.5A GFCI trips 63A pole interrupting (+)

I'd rather the disconnect was higher current than 30A.


Since two strings being paralleled, OCP isn't required.

Only issue (other than nuisance tripping) that I think of is the polarized 30A breakers. Let's say one string was somehow shorted, sinking current from the other string. Open breaker of other string and it is able to interrupt current. Open breaker of shorted string and it is carrying current in backwards direction, may not interrupt successfully.

Separate breaker poles is convenient for testing, but does appear to have this issue. Don't know if the problem has ever occurred anywhere other than my head (requires a shorted string, not just somewhat lower voltage.)
Click to expand...
That's why you need to put these in decent metal enclosures imo, like the Midnite solar range. For possible breaker fire.
 
Hedges said:
Close, then with 27.4A Isc.

Oh, there is a non-polarized 30A with (+) and (-) going through the two poles.

0.5A GFCI trips 63A pole interrupting (+)

I'd rather the disconnect was higher current than 30A.


Since two strings being paralleled, OCP isn't required.

Only issue (other than nuisance tripping) that I think of is the polarized 30A breakers. Let's say one string was somehow shorted, sinking current from the other string. Open breaker of other string and it is able to interrupt current. Open breaker of shorted string and it is carrying current in backwards direction, may not interrupt successfully.

Separate breaker poles is convenient for testing, but does appear to have this issue. Don't know if the problem has ever occurred anywhere other than my head (requires a shorted string, not just somewhat lower voltage.)
Click to expand...
Yes, I did get pretty close to the 27.4 Isc, about 10.2% above. Should be enough with this application. If I get nuisance trips, I'll go a little higher. I won't know until next June when I finish wiring the control 1000011646.jpg1000011647.jpgpanels inside the building. The building is getting a complete restoration, and I wanted to take it off grid first. Thanks for your comments.
 
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