What are the + and - signs on my breaker for?

[Halfcrazy]

IMPORTANT! Polarity of the din rail DC breakers.  The DC breakers supplied by MidNite Solar are custom manufactured in Lesotho Africa by CBI. These breakers are polarity sensitive. This means that they need to be installed correctly in order to insure that they will be able to trip if called upon to do so. In a PV combiner the + sign marked on the breaker connects to the PV positive output. The same breaker when hooked up to the battery circuit (not in a PV combiner) hooks up a little different. The + sign hooks up to the battery plus. This hook up is not obvious. The + sign designates the highest potential should be connected there. This is an easy one to determine in a PV combiner. Follow the current path through the combiner, into the PV input of a charge controller and out of the controller to an output breaker and then into the battery plus. You would think that the end of the output breaker connected to the controller would be at a higher potential than the battery plus. In normal operation this is true. The main job of this output breaker is to trip when and if there is a catastrophic failure. (Any manufacturer of power electronics will tell you that power electronics can fail). If the output breaker fails to trip, you are at risk of fire from the output wires burning up. When a charge controller fails, they always short from positive output to negative output. Since these two terminals inside the charge controller are normally connected up to a very large battery bank, you have a direct short across the battery bank if the controller fails. During this condition, the controller is acting like a piece of wire. The battery positive terminal is the highest potential! Make sure that the plus (line) of the breaker is connected to the battery plus terminal. If the breaker is connected backwards, it can fuse in the closed position as it attempts to open. That could ruin your entire day!

[Westbranch]

so that being true there are a bunch of CAD drawings that may not follow what you have above??

ieMNPV6 as DC Distribution on this page 

http://www.midnitesolar.com/documentsA.php?menuItem=documents&docCat_ID=7&docCatName=AutoCad%20&%20Visio%20Drawings

PS which side of the breaker is the (+) side ON? OFF?

[mtdoc]

IMPORTANT! Polarity of the din rail DC breakers.  The DC breakers supplied by MidNite Solar are custom manufactured in Lesotho Africa by CBI. These breakers are polarity sensitive. This means that they need to be installed correctly in order to insure that they will be able to trip if called upon to do so. In a PV combiner the + sign marked on the breaker connects to the PV positive output.

OK - just to be clear - since I am about to wire up my system expansion....

If I follow the directions above and mount my breakers in my MNPV6 with the combined PV positive output bar above the breakers - the breakers will need to be "upside down"  to get the + side mated with the combined PV positive output bar - by this I mean the words on and off will be upside down.

I ask because this is the opposite of what the picture on the first page of the MNPV installation instructions shows - see HERE   

[Robin]

Please install exactly like shown in the instructions. Combiners are a little funny. In normal operation you need to have the PV array connected to the bottom of the breaker where the + sign is at. The top of the breaker gets the busbar. When and if a fault occurs, the faulted string will be connected up backwards until the fault is cleared. This is the abnormal operation. It works, trust me. The NEC is going to require non polarized breakers in the NEC2014. I am not sure what we are going to do for breakers? People are working on the issue, but there is nothing available yet.
After having sold over a million breakers for combiners, I have yet to hear of one not working properly..

[mtdoc]

Thank you Robin.

But I' still confused..

Please install exactly like shown in the instructions.

Do you mean as described by the words in the instructions (and in Ryan's post) or as shown in the picture on page 1 and the wiring diagrams?

Sorry to be splitting hairs but the pictures show one thing and the directions say another....

Thanks - I really appreciate the help (and the great products!).

EDIT-  Ok now that I read Ryan's post and the instructions again - I see it could be interpreted to mean the same as the pictures.  The problem is the words "In a PV combiner the + sign marked on the breaker connects to the PV positive output" . I initially thought "PV positive output"  meant the combined output at the busbar but it must mean the output from the panel. This makes sense with the idea that the panel is at a higher voltage (potential) than the battery side.  (and matches the pictures).

OK so I think I've got it.  Sorry for any confusion - it's a bit tricky with the wording ( and looks like Westbranch had similar issues).

Thanks again for the great products and support!

[Rybren]

Okay, I'm really confused.

In the hard copy instructions that came with my E-Panel and in a set that I downloaded, both the diagram and the written description show the wiring going from the PV Plus Busbar to the "-" side of the DIN rail breaker:

  "The + (line) marking on the breaker would seem to indicate that you should connect the PV+ to this terminal since the PV+ is the highest potential in the system. Our testing shows this would be incorrect...
4. The + side of the PV in breaker goes to the charge controller PV+ input terminal."

However, in a different set of instructions that I downloaded, the directions state just the opposite:

"The + (line) marking on the breaker would seem to indicate that you should connect the PV+ to this terminal since the PV+ is the highest potential in the system. Our testing shows this would be correct. The + side of the breaker needs to be connected to the highest potential per the breaker instructions.
5. The - side of the PV in breaker goes to the charge controller PV+ input terminal."

Based on what I've read and my own intuition, I believe that the second of instructions is correct, but I'd like to be 100% certain before actually installing anything.

Thanks,

Jerry

[Halfcrazy]

You are correct. The + sign on the CBI breaker always points to the side with the greatest potential IE the solar panel or battery etc

Ryan

[TomW]

Rybren;

In any "normal" application with polarized components the + would be connected to the "Most Positive" connection point.

Unless they totally went against convention marking that breaker that is how it should be connected.

That is how I connected mine.

Tom

[TomW]

Gee, Ryan got his post in while I was typing mine.

Tom

[Rybren]

Thanks guys.  I was 99% sure that I managed to receive some old and incorrect instructions, but that 1% of uncertainty was still there.

Cheers,

Jerry

[Endurance]

I am installing a Classic 150 next week on a 12-volt system. It will have a 50-amp and a 100-amp breaker in addition to the 15a breakers at my combiner.

The 50-amp breaker goes in the wire from my combiner to my Classic 150. The wire from the combiner would have the higher potential so it would go to the + side of the breaker. So far so good.

For the 100-amp breaker between my controller and my battery bank, things get less clear. Since the controller is "pushing" power to the bank, it would seem the controller side of the breaker would have higher potential and would get the + side of the breaker.  But that contradicts putting the + on the battery side of the breaker.

I think I'd rather get this right than cause a fire on my boat. Ryan, would you mind helping with my confusion?

[Halfcrazy]

Here is a link to a document I did on this http://kb1uas.com/MidNite/Breaker%20Sizing.pdf

On the 100 amp breaker if it is a Din Rail the Battery goes to the + side of it. If it is the panel mount the polarity does not matter.

Ryan

[nigel]

Ryan I wasnt aware of a single din breaker currently available over 63 amps.

we need clarity on this issue I thought the highest pd ie voltage went to the positive side .

[Halfcrazy]

Nigel
We now have 80 and 100 amp breakers. They are 2 poles wide though http://www.midnitesolar.com/productPhoto.php?product_ID=364&productCatName=Breakers&productCat_ID=16&sortOrder=17

As far as the + side of the din rail. The rule of thumb is to attach the side with the greatest potentil or the current source to that side.

Ryan

[vtmaps]

In a PV combiner the + sign marked on the breaker connects to the PV positive output.

I'm bringing back this old thread because the topic came up on the NAWS forum and I am still confused.

If I am using a breaker (in the combiner) as a switch to turn on/off a single string of panels, then the string of panels certainly has the higher potential and the breaker should be wired as you explain.

However, I was under the impression that the PURPOSE of having string breakers in a combiner box is to provide overcurrent protection to a faulted string.  If a string faults, the current flow that you need to break is flowing backwards through the string.  This means (as I understand it) that the breaker should be installed with its polarity reversed from what you explain.

What am I missing?

--vtMaps