Combiner Box Help

[Brucey]

Hmm. I would say you do what works for you. Look at the photo of my Double Pole polarized breaker. There is both a -- and a ++ on the top and bottom. So your convention would result in a null situation with no clear answer for the installer since the ++ would be on the bottom too. But what is the "potential" across the the PV--? Isn't it the same as across the PV++, just in a different direction?

If anyone has any doubts about how to install a Midnite Solar polarized breaker, then contact Midnite Tech support, they get on the phone and are very helpful.

If you look earlier in the thread at my photo posted on the left using the double pole breaker, you will see what I believe is the proper best practice for wiring a fused and breaker polarized combiner box for today's higher voltage world. The photo on the left was wired in 2016 for a low voltage ( less than 150 volts) parallel string combiner box to a stand alone MPPT charge controller.

I believe those double pole breakers are usually run with a bridge on the bottom, to bump up the voltage rating by running in series. So to use them as individual breakers you'd need to have one from the top and the other from the bottom to take the polarities into account.

 

[glandpuck]

I believe those double pole breakers are usually run with a bridge on the bottom, to bump up the voltage rating by running in series. So to use them as individual breakers you'd need to have one from the top and the other from the bottom to take the polarities into account.

Well, thanks for your comment. But the breaker in my photo is already rated for 600 volts DC. I don't think many strings are going beyond that rating yet.

 

[Brucey]

Well, thanks for your comment. But the breaker in my photo is already rated for 600 volts DC. I don't think many strings are going beyond that rating yet.

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.

 

[cdsolar]

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, using the clip to tolerate 600V. 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 separate 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.

 

[cdsolar]

I am sorry if I am sounding a bit overbearing, if you will. A polarized DC breaker wired backwards may not be able to extinguish the arc in an over current situation. see this video:

 

[Brucey]

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.

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.

 

[glandpuck]

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

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.

 

[glandpuck]

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

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.