120/240 Breaker for 24vdc Array Wires

[heirloom hamlet]

Can a standard breaker box and breaker be used as fuses for the 24vdc 10awg wires straight from the array?
I have used 250w 24v panels 2S4P (2000w, 75.02v, 33.08a). 10awg wires are now going straight to the MPP A-I-O. Can a breaker be used or only dc fuse of some sort?

 

[gnubie]

You will need DC rated breakers. An AC rated breaker relies on the fact that the current regularly falls to 0 amps, DC doesn't do that and will sustain an arc until something melts away and/or catches fire. 75VDC is more than enough to cause a 120/240VAC breaker to fail.

When sizing the DC breaker you should ensure that it is rated to break the Voc and Isc of the array.

 

[JoeHam]

I bought this DC breaker and was pleasantly surprised when it arrived to see it was an actual Schneider brand:

Circuit Breaker 2P 250V 16A Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System Din Rail Mount - - Amazon.com

Circuit Breaker 2P 250V 16A Low-voltage DC Miniature Circuit Breaker For Solar Panels Grid System Din Rail Mount - - Amazon.com

www.amazon.com

 

[heirloom hamlet]

You will need DC rated breakers. An AC rated breaker relies on the fact that the current regularly falls to 0 amps, DC doesn't do that and will sustain an arc until something melts away and/or catches fire. 75VDC is more than enough to cause a 120/240VAC breaker to fail.

When sizing the DC breaker you should ensure that it is rated to break the Voc and Isc of the array.

Thanks, man. Are dc breakers hard to come by, do you think it would be easiest to just get an inline fuse (I assume for the positive wire)? I see they have them reset-able now.

 

[gnubie]

DC breakers are readily available, JoeHam linked to one. One advantage of a breaker is you can use it as a manual switch too.

 

[Deleted member 4428]

Square D QOU are DC rated to 48 VDC 70 amps. I think the QO are as well. Available off the shelf at Lowes and Home Depot. Do not use the Square D home line for DC.

 

[Deleted member 4428]

My bad, didn't read enough of the thread. Sorry, i'll zip it.

 

[heirloom hamlet]

DC breakers are readily available, JoeHam linked to one. One advantage of a breaker is you can use it as a manual switch too.

I see that, and I appreciate your thoughts.
I wonder if I could get your opinion on the size I should get. My panels are 8.27a, so 33.08 is my max, which of course I will never get, especially on my used panels.
Since I am really just protecting the 10awg wire, would you say 30a was my ideal, or could that give me fits?

This? :

https://www.google.com/url?sa=t&sou...FjAAegQIBBAC&usg=AOvVaw2bdV8qncDysN1uN0QQaTXx

[/URL]

 

[JoeHam]

The link I posted also has higher amperage ones available. Rated for 250v DC

I found them by searching google for the Schneider model number shown on the breaker.

 

[tictag]

I believe you can buy, what are they called, 'combiner boxes'? Which I'm guessing can be purchased pre-populated with appropriate DC breakers. Well, I mean you can by 'consumer units' for AC applications that come pre-populated. Might be worth a google search.

Midnite and the Alt-E store are coming to mind.

 

[erik.calco]

Can a standard breaker box and breaker be used as fuses for the 24vdc 10awg wires straight from the array?
I have used 250w 24v panels 2S4P (2000w, 75.02v, 33.08a). 10awg wires are now going straight to the MPP A-I-O. Can a breaker be used or only dc fuse of some sort?

Just get an enclosure with a DIN rail, and get MidNight Solar's 150V DC breakers. They run for $14-20. I just ordered another off ebay yesterday.

Note that 10 AWG fits in it. 4 AWG does not. I have notes from a tech discussion I had with MidNite if you need to know exactly what can fit in it. I think it can fit 6, but have to double check.

Note that if you get into combining, their 3 prong metal piece for combining that comes with their 300V enclosure fits in their 150V breakers. I got their outdoor rated combiner box new on ebay for $68. That can take 4 AWG. So you can combine 10 AWG PV into 4 AWG.

There is discussion about some breakers at HD being rated for DC. But, all the ones I looked at were limited at 48V.

MidNite has the baby box DIN enclosure. It's not much cheaper than the combiner enclosure and is not rated for outdoor. I got mine for $40. That said, it's nice if you need a small indoor form factor, such as for in an RV.

I've seen people install DIN rails in their own enclosure if you really want to get DIY. I'm happy with Midnite Solar's enclosures. Very well designed.

If you are new to DIN, it is just a rail that the breakers snap onto. No power goes through the rail. It is just for mounting. The breakers have an opening at the top and the bottom for terminal connections that you screw in, like you would with one side of a normal AC breaker.

 

[JoeHam]

Here is the DIN box I am using. Comes complete with DIN rail installed.

Amazon.com

 

[heirloom hamlet]

I'm trying to determine the sizing for my panels and I'm a bit confused.
I'm 250w (x8), 2S4P. So the current top is 33.08a and the voltage is 75.02v.
But on the LCD screen on my MPPT it says "PV" and "Batt" above that. And I've seen it as high as the mid 50s amperage. When I use my volt meter to check the PV inbound wires it always reads around 12 or 13a.
The same display for the voltage might say 55v, which makes sense (75% efficiency), and the volt meter reads that same figure.
Am I misunderstanding what the display is showing, is it not the arrays input amperage?