DC breaker markings?

Hi, I believe that the + marks are indicating the line (battery) side of the breaker. Connect the item being protected to the other side.

The + is the higher potential side (PV input or Charge Controller output).

When MidNite Solar was doing ETL testing on the line of breakers you are using, they wired a breaker incorrectly and it melted down in the closed position! (Luckily, they had a knife switch in the circuit.)

Thanks, Guys! I opened this thread idly, just for something to look at and it's really helpful!

So the +++ on a DC Breaker is what "Line" would be in AC wiring, correct?

Now let me try a question since you seem to be UP on this stuff: Same true of AC Breakers? I don't much care for the way our IOTA Load Center is set up. It's Converter/Charger, AC Breakers and DC Fuses all in one. AC portion uses 2-in-1 breakers. Its four branch circuits are "15/15" (each protecting two 15A branches) but Main and A/C are protected by a "30/20" with 30A being Line into the Panel and 20A protecting the A/C. This means the 30A side is being fed through what's normally "Load"(the screw terminal) and powers the box buss through what's normally "Line" (the stab down terminal). Is this actually acceptable? I suppose IOTA got some kind of "approval" for their design, but it sure makes me wonder.

And... I really don't like the 2-in-1 breakers, especially the 30/20, in that tight space. The RV runs right at max in summer with A/C so both sides of that 2-in-1 are close to capacity. I think the 30/20 is getting warm enough to cause false tripping. What do you think?

The +++ isn't so much line as it is higher potential (i.e. higher voltage). For typical RV DC power distribution, this does happen to be the source side of the circuit, but it would be reversed if one had a positive ground system for some odd reason—which, while unique and annoying, is not a safety issue or a violation of any code I know of.

AC doesn't have polarity requirements like this, since the voltage is constantly alternating between positive and negative. So far as the breaker is concerned, there is no real difference between the line or the load side, and AC breakers and switches will work in either orientation.

AC breakers (at least residential ones with a thermal-magnetic curve) are not generally expected to hold their full current rating for long periods of time without tripping when they are installed in a panel. I think the typical rule of thumb is 80% continuous or so. That said, if the breaker is noticeably heating, it would not hurt to check that the wire and buss bar connections are all good and tight and undamaged.

Thanks people. Now I know that have to reverse one DC breaker as it worked as a switch only.

Thanks X2! I think my 30/20 is warming itself and for now I plan on running a computer fan over them in summer. Little 80mm fans pull 0.16A at 12VDC. I'll just tap onto one of the 12VDC fuses right there in the IOTA unit.