Why you don't use AC rated equipment on HV DC

I have some solar panels that feed charge controllers at over 100V DC (4 panels in series and 2 or 3 strings in parallel) and to test out shading effects, etc. I added some additional breakers for each string as I had some "cheap $1 breakers"... with the intent of not using them as live switches as I had a separate DC rated breaker that I could use to switch off the HV side (should not do anyway), however I ended up being a bit lazy and switched one of the AC breakers when it was full sun.... aftere about a second of arcing internally I switched it back on... oops. damage done.

Ever since then the thing would trip "randomly" and after a period of time at high load.. so to carry on with an experiment I kept switching it back on each day (more than once on some days) and wondered if it would melt or set on fire (the wiring is all in a steel enclosure and I like experiments...) after a few months I thought it was time to see what the damage is as it never melted or set on fire.....





Interestingly ths was usually being tripped at about 110V and between 3-7A each time, so would have arced a bit on each trip and there is relatively little damage as I was expecting a bit more or a burn to the case !

Yeah those contacts are looking pretty pitted!

Here's a fun video of dodgy "DC rated" isolators (4 in series, 200V each) not working as they should:


Not sure I'd be holding that thing....

AC breakers rely on the zero crossing of the sine wave to extinguish the arc.

2 layers of gloves, they look like pro live working gloves.

Another thread that reminds me that I should at least own some more personal electrical saftey gear... specifically gloves.

I got nice insulated screw drivers and try to keep my projects <60 VDC, but sometimes you just gotta start poking around at high HV DC stuff.

Nice breaker information too... DC is some serious stuff. I decided for all my DC breakers and saftey equipment, I will be buying from established brands like Eaton, Bussman, Blue Sea, ABB, Schnider, GE or whoever else has a track record for this sort of thing.