can this breaker be used as a double pole disoconnect

[John Frum]

Product - MidNite Solar

MidNite Solar Product Page.

www.midnitesolar.com

Notice the jumper on the bottom.
Notice the positive and negative are reversed top to bottom.
With the breaker closed and the jumper removed is there continuity between top left and bottom right?
I can't believe that there is so I suspect positive and negative should be line and load.
Midnite solar's doco doesn't have much to say on the subject.

@NorthTown2022

 

[John Frum]

Just talked to midnite tech support and its two 150VDC single pole breakers in series.
So it can't used as a double pole breaker because the string voltage will be too high.

 

[HRTKD]

So what's the point of setting the breakers up that way? Legitimate question. I really don't understand why it's set up that way.

 

[John Frum]

So what's the point of setting the breakers up that way? Legitimate question. I really don't understand why it's set up that way.

According to midnite tech support 2x 150 volt breakers in series can handle 300 volts.

 

[WYtreasure]

According to midnite tech support 2x 150 volt breakers in series can handle 300 volts.

Hey John,
What product did you ultimately choose?

 

[John Frum]

Hey John,
What product did you ultimately choose?

I didn't.
This thread is about determining the capabilities of a legacy breaker, not choosing a new one.

 

[Samsonite801]

Just talked to midnite tech support and its two 150VDC single pole breakers in series.
So it can't used as a double pole breaker because the string voltage will be too high.

I remember a discussion about this some time ago. Somebody (reputable poster here) was saying it is still legit to use as a double pole (without jumper), one breaker on positive and one breaker on negative (of same PV circuit), and essentially it acts the same way, as the 300v DC breaker (using 2x 150v in series in the circuit to achieve 300v rating).

Don't chisel my words above in stone, but I might look into it.

Because it makes sense, both breakers are still in series on the same circuit, if you pointed them the same fashion regarding polarity (as with or without the jumper), and breaking at the same time, so it should have the same effect as being in series right next to each other, as with when the jumper is being used.

 

[John Frum]

I remember a discussion about this some time ago. Somebody (reputable poster here) was saying it is still legit to use as a double pole (without jumper), one breaker on positive and one breaker on negative (of same PV circuit), and essentially it acts the same way, as a 300v DC breaker (using 2x 150v in series in the circuit to achieve 300v rating).

Don't chisel my words above in stone, but I might look into it.

Because it makes sense, both breakers are still in series on the same circuit, if you pointed them the same way in polarity (as with or without the jumper), and breaking at the same time, so it should have the same effect as being in series right next to each other, as with when the jumper is being used.

I'm skeptical that 2 150VDC breakers in series can magically tolerate 300VDC.
I would need the magic explained.

 

[Samsonite801]

With the breaker closed and the jumper removed is there continuity between top left and bottom right?

There isn't, it's open, I have 6 of this style breaker, and just checked it, here's a pic...

 

[Samsonite801]

I'm skeptical that 2 150VDC breakers in series can magically tolerate 300VDC.
I would need the magic explained.

Yeah on mine, one of these complete 300v modules consist of 2x 150v breakers, but the way they shipped like this, there is a sticker on the front showing 300v (which is what I had ordered)...

 

[Samsonite801]

I'm skeptical that 2 150VDC breakers in series can magically tolerate 300VDC.
I would need the magic explained.

In this case, I believe it has less to do with the contacts being able to support or 'tolerate' that voltage level in relation to its respective max current carrying capacity, but more to do with the arc-breaking scheme (in order to support that high of voltage - arc potential), having 2 breakers in series break at same time (set with those polarities), it has a more reliable strategy (with magnets) to absorb and extinguish the arc at that voltage level, than it could with a single breaker schema.

 

[Samsonite801]

Check this video out I saw some time back when I was into selecting my Midnite Solar MNPV6-Disco DC combiner box stuff...

I'm starting the video at 3:27 talking about the subject here, but you can rewind later if you want to see the whole video (I recommend watch the whole thing if you got the time)...

 

[Prince Of Darkness]

To me, MidNite breakers (as are all of their other products), are the real deal.

Anything that needs an NRTL cert, gets it, usually by ETL.

The pics of breakers in this conversation, show the ETL logo, and file number (generally).

From the MidNite Solar site for these breakers,

"MidNite's breakers are rated to break the full rated load at the rated voltage repeatedly, with NO DAMAGE. Always use a properly sized breaker for disconnecting.

MNEPV breakers are the same as CBI QY breakers except the standard used is inadequate for the solar industry. MidNite breakers have been evaluated by ETL to 300VDC and are listed for US and Canada. All of the NRTL listings still apply. Breakers ordered under the CBI part numbering system will not be listed for 300VDC and in many cases are not suitable for the solar industry".

I would feel uncomfortable using most "DC" breakers that I've seen from China. Just because there are so many different brand names, and often, they are very thin on specs (that I can read). The risk just seems too great, IMO.

AND, with MidNite there is a US phone number, with some real help, on the other end on the line.

MidNite Fan-person, POD.

 

[Samsonite801]

To me, MidNite breakers (as are all of their other products), are the real deal.

Anything that needs an NRTL cert, gets it, usually by ETL.

The pics of breakers in this conversation, show the ETL logo, and file number (generally).

From the MidNite Solar site for these breakers,

"MidNite's breakers are rated to break the full rated load at the rated voltage repeatedly, with NO DAMAGE. Always use a properly sized breaker for disconnecting.

MNEPV breakers are the same as CBI QY breakers except the standard used is inadequate for the solar industry. MidNite breakers have been evaluated by ETL to 300VDC and are listed for US and Canada. All of the NRTL listings still apply. Breakers ordered under the CBI part numbering system will not be listed for 300VDC and in many cases are not suitable for the solar industry".

I would feel uncomfortable using most "DC" breakers that I've seen from China. Just because there are so many different brand names, and often, they are very thin on specs (that I can read). The risk just seems too great, IMO.

AND, with MidNite there is a US phone number, with some real help, on the other end on the line.

MidNite Fan-person, POD.

Yeah exactly, this is what I concluded after all my research into DC breakers for my PV runs on my final system (since I'm up into the 300v breaker category).

For my temporary RV solar solution using the Victron SCCs on 12v setup, I went ultra cheap and purchased 2 Eco-Worthy combiners (which have a 63a breaker, fuses for each string, built-in lightning arrestor)... Great value, but for my permanent 48v home system, I decided to run only with Midnite Solar combiners, 300v breakers, Midnite Solar surge arrestors, because I can trust they will operate to the rating.

On my cheap Eco-Worthy boxes for my 12v RV temp system, I always shutoff the PV draw in the Victrons before I go shutoff the breakers in the combiners, because I'm afraid to turn them off under full PV current hehe...

 

[400bird]

Well crap, I'm glad this came up, but it throws a wrench...

I purchased a midnight solar 15 amp 300 volt breaker without doing any research. I saw the dual pole and thought I could use it as my "required" DC disconnect.
I've got to be able to disconnect all non grounded conductors. So, both PV positive and negative.

I didn't realize the dual pole was to run the positive through the breaker twice.

I think the breaker would still function and the polarity is correct if I remove the jumper and run it as a dual pole with positive and negative each through one side of the breaker.

The DC PV is about 120 vdc at the coldest VOC, so I'd be fine at the single breaker's 150 volt rating.

 

[Samsonite801]

Well crap, I'm glad this came up, but it throws a wrench...

I purchased a midnight solar 15 amp 300 volt breaker without doing any research. I saw the dual pole and thought I could use it as my "required" DC disconnect.
I've got to be able to disconnect all non grounded conductors. So, both PV positive and negative.

I didn't realize the dual pole was to run the positive through the breaker twice.

I think the breaker would still function and the polarity is correct if I remove the jumper and run it as a dual pole with positive and negative each through one side of the breaker.

The DC PV is about 120 vdc at the coldest VOC, so I'd be fine at the single breaker's 150 volt rating.

Yeah that's what I was trying to say in Post #7 here, that I don't think it matters where the 2 breakers are in the circuit (like having one on positive, and one on negative), I think it would still function as a 300v having both in the same circuit, and both breaking connection at same time (as they have a connecting bar on the switches)...

Like it doesn't matter that the 2 are sitting right inline on the red wire, or having one on each wire, farther apart in the circuit, they are still in series and interrupting with a larger gap in two places, so the 300v rating should still apply anyways.

 

[400bird]

Yeah that's what I was trying to say in Post #7 here, that I don't think it matters where the 2 breakers are in the circuit (like having one on positive, and one on negative), I think it would still function as a 300v having both in the same circuit, and both breaking connection at same time (as they have a connecting bar on the switches)...

Like it doesn't matter that the 2 are sitting right inline on the red wire, or having one on each wire, farther apart in the circuit, they are still in series and interrupting with a larger gap in two places, so the 300v rating should still apply anyways.

I don't even need the 300 volt rating, but good point, the current still flows in the same direction no matter where the source is in the circuit.

 

[OzSolar]

FWIW, back in the days before string inverters came with integral DC disconnects we were allowed to use a 3 phase AC/DC disconnect. Square D publised a special paper on how to wire it that we could provide to insectors. Positive was ran in series through all poles.

 

[OzSolar]

Bumped into this a while back. It's interesting to me that the QO load center you can find in your local big box store for less than $50 is rated for up to 125VDC.

The QO single Phase Main Lug Load Centers are SQUARE D CERTIFIED for use on 125 V DC systems. The load centers listed ARE NOT MARKED for use on this voltage system, however are suitable for the application. The positive (+) conductor should be connected to one phase lug, while the negative (-) conductor should be connected to the other phase lug. USE QO 2-POLE BRANCH BREAKERS ONLY. QO branch breakers, 10-70 ampere, are also SQUARE D CERTIFIED for use on 125V dc systems. Short circuit current rating is limited to 4,000 amperes (10-30 ampere) or 10,000 amperes (35-70 ampere) when used on 125V dc.

Are QO load centers suitable for use on a 125V DC application? | Schneider Electric USA

 

[Hedges]

Just talked to midnite tech support and its two 150VDC single pole breakers in series.
So it can't used as a double pole breaker because the string voltage will be too high.

I remember a discussion about this some time ago. Somebody (reputable poster here) was saying it is still legit to use as a double pole (without jumper), one breaker on positive and one breaker on negative (of same PV circuit), and essentially it acts the same way, as the 300v DC breaker (using 2x 150v in series in the circuit to achieve 300v rating).

Because it makes sense, both breakers are still in series on the same circuit, if you pointed them the same fashion regarding polarity (as with or without the jumper), and breaking at the same time, so it should have the same effect as being in series right next to each other, as with when the jumper is being used.

Well crap, I'm glad this came up, but it throws a wrench...

Yeah that's what I was trying to say in Post #7 here, that I don't think it matters where the 2 breakers are in the circuit (like having one on positive, and one on negative), I think it would still function as a 300v having both in the same circuit, and both breaking connection at same time (as they have a connecting bar on the switches)...

Yup, it'll work fine as a string disconnect, as shown in OP's post or rewired to open both positive and negative leads. Two 150V poles in series, ganged to trip together, will interrupt current the same no matter where each one is in the circuit (so long as in series with the circuit including a fault they might be interrupting.)

When three or more strings are in parallel, I don't believe multiple separate polarized breakers can be relied on. The PV string that is shorted and being backfed trips, but won't interrupt the arc because current is flowing in wrong direction. Ganged with the other two breakers I think it would work. (not the OP's situation.)