I had a DC breaker burn up. Why?

[Sticky1]

That's the ones I'm using for my battery breakers on different systems. I had the same problem figuring out how to wire them. I don't remember how I ended up wiring them.

Well wtf …. That does t help…

 

[Sticky1]

Yes supply in the top and load in the bottom.

Thanks

 

[Crowz]

Well wtf …. That does t help…

Sorry

I'd of gone and looked but I put them in a water proof box so not so easy to look.

 

[Hedges]

If you look at the manufactures diagram it doesn’t make any sense positive has an arrow going into the breaker on top negative has an arrow going out of the breaker on top. Or does it even matter

It matters for ability to interrupt an arc, especially high fault current like a dead short drawing current from battery.
It has a magnet to deflect the arc, based on which way current is flowing.

If connected to battery, with battery positive connected to "+" and battery negative connected to "-", then if a short occurs on the other side, it will have the best chance of successfully stopping current flow.

If used in a bidirectional application like between battery and SCC, that orientation might work Ok. Could be a problem if battery BMS was shut off and the battery side was zero/shorted, and you tried to interrupt current from charge controller into that short.

A non-polarized breaker should be used for bidirectional applications.

If used for PV strings, of course PV string is the source with highest positive and lowest negative voltage. Unless one string gets shorted and the others dump into it, so the breaker is expected to trip and protect against a fire.

Again, non-polarized breaker should be used if protecting multiple paralleled strings.

I think people have been getting away with using these polarized breakers in PV/battery systems for years. But we could easily design a fault condition which would cause them to burn. Don't know if any have occurred unintentionally.

 

[Sticky1]

Thanks for the info

 

[Tomthumb62]

Yes supply in the top and load in the bottom.

This. Yes they are not bidirectional, so you do need to wire them properly.

 

[Sticky1]

Got it. One string up

 

[Whats_per_question]

Things I've ruled out:
1. Because the matching Negative breaker shows no signs of heat or issues, I think it's safe to rule out it was not an overload "surge" or sizing issue with wire or breaker. 8 gauge wire on a 20 amp load is oversized and should create no heat at that load.
2. Trip extinguish was not it, as the breaker was not tripped.

To me it's one of two things that caused this:
1. One possibility is, as many of you suggested, not a good wire connection on that particular breaker lug causing heat build up over time and eventually a melt down. As I've stated the wire is still in there and solid. Did it fuse during melt down, maybe....
2. Breaker was defective and did not make good internal contact to the terminal end that melted. There was internal arcing and that is ultimately where the circuit failed, but I can't say for sure the heat build up started there.

What I think I'll do.
1. I'm going to install Ferrule ends on the cables going into the breakers and torque the connections down good
2. I'm going to leave the cover off for now and monitor the terminal/breaker temps throughout the peak of the day. I have a spare matching 63 amp breaker, I'll use for now. These breakers are used as disconnects for PV, not over current protection, so oversized breaker should not be of concern. I'll report my findings.

Super late to the party, but given i've seen one of these recently ...
My 2c;
- Commissioning the system (not sure if you did this) might have caught the thermal buildup on that positive breaker terminal, but probably only if you had a thermal camera at your disposal, or the heat dumped on that terminal was high enough to feel with your hand or smell the plastic sweating.
- Always use ferrules; they are cents per connection, but give you additional protection from not only stray copper strands that you might not see in the darkness of an enclosure, but also that little band of color (colour for the Kiwis/Aussies/Brits) on the ferrule might remind you that a black wire isn't actually negative in some cases.
- Re-check your commissioning checklist on the first cranking day - connections that were fine at 12A might need tightening at 60A