I had a DC breaker burn up. Why?

[Mattb4]

About to wire up a similar CHTAIXI breaker. So you’re saying that panels should be wired to the - connection port on top and the output (to SCC in my case) wired to the + port on bottom?

View attachment 153318

Do not like how they label that single pole breaker. A person not knowing better might think you hook up positive to bottom and negative to the top. You want the same polarity coming out of the breaker as going in. If that is the negative wire from panels it continues to be the negative wire to the SCC. Typically breakers are directional with the throw switch in On position towards line. In Off the throw switch is towards load. Since the solar panels are the supply that makes them line and your SCC is load.

Personally I would use a 2 pole DC breaker to isolate panels and SCC. The one pictured looks more appropriate for a load breaker in a automotive/marine application where there is a common ground (neg or pos) so you just switch off the one input.

 

[Quattrohead]

About to wire up a similar CHTAIXI breaker. So you’re saying that panels should be wired to the - connection port on top and the output (to SCC in my case) wired to the + port on bottom?

View attachment 153318

Be very wary of these breakers as I have had one fail on me. I don't know what the difference is between the light green and the blue ones but all of my blue ones have been 100% so far.

 

[rhino]

As a followup, I installed the same model of breaker only 63amp rating "I had it already". I installed wire Ferrules on all the 8 gauge cables. During peak of the day the terminals get about 125 degree F. There is about 19 amps going thru it. The smaller breakers with half the load are about 110F. The big 125 amp breaker is the hottest at 135 to 140F, with about 50amps going thru it.

Would be really interesting if you could get one of the Midnite/Carling breakers and see how they compare.

 

[Tomthumb62]

Do not like how they label that single pole breaker. A person not knowing better might think you hook up positive to bottom and negative to the top.

I agree, should just be labeled supply in and load out.

Since the solar panels are the supply that makes them line and your SCC is load.

Thank you, that’s what I thought but great to confirm it.

Personally I would use a 2 pole DC breaker to isolate panels and SCC. The one pictured looks more appropriate for a load breaker in an automotive/marine application where there is a common ground (neg or pos) so you just switch off the one input.

My use case is only as a PV disconnect. PV is only 400W. Currently there is a self resetting 30A fuse on the PV + line, as instructed by WindyNation. I will place the fuse BEFORE the single pole breaker. Would it still be necessary to use a dual pole in such a situation? I mean, how can current flow through the - PV line if the + line is disconnected?

But maybe I’m thinking about this like you said too much like 12v automotive since they’re isn’t a common ground here?

 

[OzSolar]

My use case is only as a PV disconnect. PV is only 400W. Currently there is a self resetting 30A fuse on the PV + line, as instructed by WindyNation. I will place the fuse BEFORE the single pole breaker. Would it still be necessary to use a dual pole in such a situation? I mean, how can current flow through the - PV line if the + line is disconnected?

But maybe I’m thinking about this like you said too much like 12v automotive since they’re isn’t a common ground here?

Why not be safe and use a nice heavy duty disconnect? Below is rated for up 250VDC is super well built, I would never trust my life or property to all those crappy polarity sensitive breakers people keep using.

Siemens General Duty 60 Amp 2-Pole 2-Wire 240-Volt Non-Fusible Outdoor Safety Switch RBPU LNF222RAU - The Home Depot

General Duty Safety Switches are intended for applications where reliable performance and continuity of service are needed. But where duty requirements are not severe and usual service conditions prevail.

www.homedepot.com

 

[Tomthumb62]

Why not be safe and use a nice heavy duty disconnect? Below is rated for up 250VDC is super well built, I would never trust my life or property to all those crappy polarity sensitive breakers people keep using.

Siemens General Duty 60 Amp 2-Pole 2-Wire 240-Volt Non-Fusible Outdoor Safety Switch RBPU LNF222RAU - The Home Depot

General Duty Safety Switches are intended for applications where reliable performance and continuity of service are needed. But where duty requirements are not severe and usual service conditions prevail.

www.homedepot.com

I wouldn’t use something like that because it’s just too huge. This is in a camp trailer that’s used 2-3 months of the year at most (usually 2-3 weeks). Were this a 24/7 home system, then very heavy duty would be ideal. But it’s overkill for our use.

My method of unscrewing the + PV line from the SCC has worked fine so far, but I don’t think it’s all that great to be doing long term.

 

[Mattb4]

... Would it still be necessary to use a dual pole in such a situation? I mean, how can current flow through the - PV line if the + line is disconnected?

But maybe I’m thinking about this like you said too much like 12v automotive since they’re isn’t a common ground here?

Not specifically necessary but it does ensure no paths between your SCC and the panels.

 

[Tomthumb62]

Not specifically necessary but it does ensure no paths between your SCC and the panels.

Thank you. This isn’t the first time I’ve read this response. I guess I just don’t understand the logic behind it but would love to learn.

For example, if I wanted to test a solar panel, I’d put the probes directly into the ends of the MC4 connectors of the panel. But if I only put the negative probe into the negative PV wire, then zero connection is made and no energy will flow. How is this any different from only disconnecting the + PV line going into the SCC?

The only thing that makes sense (to my limited mind) is if one were to doubt that the PV disconnect on the positive line were to actually be disconnected due to a fault of the switch/breaker, then a backup disconnect (on the - line) would ensure that the circuit is truly disconnected. If this is the logic, then why not have fuses on every single panel line, both + and -, for panels in 3P or greater? Why not put disconnects EVERYWHERE that one would put one (I don’t see anyone putting a dual pole disconnect on their battery, for example). My point being is at what point is it greater safety and what point is it paranoia or simply adding more resistance or possibility of loose/poor connection?

 

[kevolones]

I have one of these (supposedly rated for 63amps) which I was using as a PV Disconnect switch next to an AIO inverter.

Last week I connected 8awg (thhn) to it and the terminals cant really clamp the wires well, as someone already mentioned here.

The "nuts" which allow the breaker terminals to tighten end up splitting the breaker case open if you try to torque it enough to properly clamp the wires (see photos). I tried with ferrules too but still doesnt pass the tug test after tightening.

Im now looking for an alternative as Im not sure I can trust these things anymore for high voltages. I dont see a lot of easily accessible options though. Looking if Midnite solar breakers would work, if not Ill go with one of those IMO PV Isolators.

 

[efficientPV]

I find it interesting that the upper metal box feed thru connectors are rusty and the lower ones are shiny. Water drip into breaker over time?

 

[Hedges]

Im now looking for an alternative as Im not sure I can trust these things anymore for high voltages. I dont see a lot of easily accessible options though. Looking if Midnite solar breakers would work, if not Ill go with one of those IMO PV Isolators.

CBI and Carling make quality breakers. Midnight relabels some, and Stella Volta carries some of those.

I've tested a few AC model magnetic-hydraulic but not DC.

Testing Magnetic-Hydraulic circuit breakers

I've built myself a circuit breaker tester. I assembled three transformers into a 3-phase wye auto-transformer, and by means of a breaker and cord/plug it can be repurposed into a current multiplier. A breaker connects X1 to H2 and H3, providing 4.7x current boost on X2 paralleled with X3...

diysolarforum.com

I also tested some Schneider Multi-9 thermal-magnetic (older aged ones which tripped early, the reason for this exercise.)

 

[kevolones]

CBI and Carling make quality breakers. Midnight relabels some, and Stella Volta carries some of those.

Good point! I was browsing stellavolta and saw a 2 pole DC breaker from CBI/Midnite that should work. It is polarized though.

 

[Quattrohead]

I have used a plumbers wrench to grip the breaker to stop it spreading like that.
It's either me or the breaker that is gonna burst a blood vessel !!!

 

[kevolones]

Local electric supply store only had these, they said installers usually buy it for PV disconnect.

It does say it can do 250 volts DC in there. What do you guys think?

 

[Hedges]

Local electric supply store only had these, they said installers usually buy it for PV disconnect.

It does say it can do 250 volts DC in there. What do you guys think?

It is made in China, and they spelled "DC" "AC"

It does indicate it is for AC circuits capable of not more than 100,000A vs. DC not more than 10,000A, which sounds reasonable.

But then it says it would be dangerous used in circuits capable of delivering more than 10,000A unless the circuit is protected with fuses having interrupt rating 10,000A.
Something about that logic doesn't sit well with me.

Don't see UL listing. If it doesn't have that, claimed performance doesn't mean squat.

Your application is PV, not exceeding 250VDC? No fault current concerns then, should be OK.
There is a similar one from a name brand.

 

[JWLV]

Just an observation.

I drew two green arrows to show where it looks like a red wire is coming from the conduit at the top and goes down behind the breaker.
I drew a blue arrow where the burned wire appears to be black.

Question: why is a black wire connected to the "+" terminal of the breaker?

 

[Supervstech]

Just an observation.

I drew two green arrows to show where it looks like a red wire is coming from the conduit at the top and goes down behind the breaker.
I drew a blue arrow where the burned wire appears to be black.

Question: why is a black wire connected to the "+" terminal of the breaker?

View attachment 169146

It used to be a red wire...

 

[Sticky1]

Not sure if this is the right place for this. Has anyone had experience with the following circuit breakers? I’ve never actually used DC circuit breakers. What’s a little confusing is the positive and negative mark on the breaker. does that mean that the feed goes into the top and the load comes out the bottom? Obviously since they’re marked positive and negative positive goes into positive negative goes into negative. 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

 

[Crowz]

Not sure if this is the right place for this. Has anyone had experience with the following circuit breakers? I’ve never actually used DC circuit breakers. What’s a little confusing is the positive and negative mark on the breaker. does that mean that the feed goes into the top and the load comes out the bottom? Obviously since they’re marked positive and negative positive goes into positive negative goes into negative. 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

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.

 

[Quattrohead]

Yes supply in the top and load in the bottom.