I had a DC breaker burn up. Why?

[mikeinnyc]

Ya I'm not willing to just slap another breaker in there and call it good. I do consider myself lucky, as this system is inside my home.

I do have a smoke detector mounted directly above this system that sends push notification directly to me. It did NOT alert. I never smelt smoke and honestly I'm not even sure when this happened, I just noticed reduced output and found this string of panels not working.

The breakers are sealed pretty well in the plastic enclosure you see in the first pic. I think the breaker housing would have contained any smoke pretty well. I do not smell any burnt smell in the room either.

use n/c alert trigger. You can also have an annoying repeating robotic Voice phone call "The roof is on fire," with sms and email. If that's running in your house you better have these alerts. I'd be happy to share my brain so that you live another day.

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The Roof is on fire some humor for the dinosaurs

 

[Mr-Sandman]

Here's some closer up pics of both the Positive and Negative of same breaker.

A few observations.

1. The negative breaker seem to be in perfect condition with no signs of heat
2. The positive breaker shows signs of extreme heat on all the metal internals. There was arcing at some point at the contacts.
3. The terminal has moved about 1/4" outward and when the breaker is closed, no longer makes contact.


Look at the difference in gap between contactor and terminal plate between these 2 breakers. I realize this is probably due to plastic melting and allowing the terminal and contact point to move outward. The question is what initially caused the heat great enough to allow that?

Positive breaker closed. Contactor no longer touches when breaker is closed "small gap". There is signs of arcing between the contactor and terminal plate.

Negative breaker makes solid connection, no heat signs and no arcing on contactor surfaces.

 

[Skypower]

Is that 8 awg in 63A breaker? Or 16A breaker? Some of these components have an extraneous "63" in the part number.
Does it say what gauges should fit?

Maybe they expected fine stranded wires and ferrules. The Europeans seem to like those.



32 ... 16 that must be amps.
Probably explains the "63A" DIN rail transfers switch I got that buzzed. Don't know what amperage it really was.
The 6 awg coarse strand I used did fit securely.

My bad!
I went out and looked at the spool I used and it’s actually #10 not 8. The number after the “C” indicates current, the other is a part number.
#10 easily fits in the terminal doubled over. The opening on the 16 and 25A look the same side by side.

 

[Skypower]

Ya I'm not willing to just slap another breaker in there and call it good. I do consider myself lucky, as this system is inside my home.

I do have a smoke detector mounted directly above this system that sends push notification directly to me. It did NOT alert. I never smelt smoke and honestly I'm not even sure when this happened, I just noticed reduced output and found this string of panels not working.

The breakers are sealed pretty well in the plastic enclosure you see in the first pic. I think the breaker box would have contained any smoke pretty well. I do not smell any burnt smell in the room either.

Probably the reason it didn’t grow to a bigger fire is the enclosure with the door closed didn’t let more oxygen in. My smoke detector is ridiculously sensitive. It went off when I was heat shrinking some cables. The smoke detector is both ionic & photonic and I added a heat detector for good measure. They are tied into the house network. Picked them up at Lowe’s

 

[TomC4306]

This only had 2 string of 2 panels on it. So about 90v at 20 amps max. I thought a 32 amp breaker would be adequate for the 20amp max load.

Apparently it WAS adequate. Breaker didn't trip.
Connection burned up.

 

[Mattb4]

Ya I'm not willing to just slap another breaker in there and call it good. I do consider myself lucky, as this system is inside my home.

I do have a smoke detector mounted directly above this system that sends push notification directly to me. It did NOT alert. I never smelt smoke and honestly I'm not even sure when this happened, I just noticed reduced output and found this string of panels not working.

The breakers are sealed pretty well in the plastic enclosure you see in the first pic. I think the breaker box would have contained any smoke pretty well. I do not smell any burnt smell in the room either.

Not being sure when it happened is a clue. The fact there was not a lot of smoke created to set off your smoke detector is another. I would guess it was a slow heat buildup from an inadequate connection. This damaged the wires insulation and further raised the resistance at the point of contact. It could even be what is holding your wire into the terminal at this point with fused materiel. At some point the heat was high enough to cause a failure in the breakers internal contact to the wire terminal.

After you lost the connection there was no more heating and any smoke/stench dissipated. When you noticed the loss of PV production is what clued you to investigate. It was likely not hot anymore by this point.

The problem with the breaker being faulty as the point of error is the greatest damage seems to be out at the wire termianl contact point.

This is just a Theory. Failure analysis like murder investigation means rounding up the usual suspects and excluding those that could not commit the crime.

 

[Mr-Sandman]

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.

 

[Hedges]

Bad breaker contacts, heated up so plastic let contact move away to the point of making an arc?
Since gap is so small, don't know what extinguished it. When sun goes down it would stop, not start up the next day. But I'd expect continuous arc to incinerate it to the point of falling apart.

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.

 

[Craig]

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, so they are not overload protection, so oversized breaker should not be of concern. I'll report my findings.

Do you have a heat temperature gun? It may be interesting to load the system as high as possible and see if any of the others get hot. It does look like your connection was good however i do know from experience as well the getting those breakers tightly connected to the wires is difficult. I like your idea of adding ferrules!

 

[Shimmy]

Do you ever operate the breakers? Sometimes you see hot contacts on breakers that sat open for a while, but that is hard to imagine happening while in service.

It is hard for me to believe that it is something other than a termination issue, but clearly these breakers are not as high a quality as one would hope from a UL breaker. This is at least the second failure of that model on the forum in the past year or so.

The best approach is to get a FLIR camera for your phone and take a look at what is going on in the other breakers.

 

[OzSolar]

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, so they are not overload protection, so oversized breaker should not be of concern. I'll report my findings.

What about switching to a disconnect since you don't need over current protection. Ii make take two depending on your wiring configuration (I didn't look close). Something like this is rated for up to 250V DC.

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

 

[OzSolar]

The best approach is to get a FLIR camera for your phone and take a look at what is going on in the other breakers.

Testing voltage drop across every connection would be a great first step.

 

[Mr-Sandman]

Do you have a heat temperature gun? It may be interesting to load the system as high as possible and see if any of the others get hot. It does look like your connection was good however i do know from experience as well the getting those breakers tightly connected to the wires is difficult. I like your idea of adding ferrules!

I do have a laser temp gun, I should be able to take pin point temps of each breakers terminals and compare.

 

[Shimmy]

I do have a laser temp gun, I should be able to take pin point temps of each breakers terminals and compare.

FWIW, remember that the temp guns laser is just to show where you are pointing. The actual cone that it is averaging is about 60º so for every 2 inches away you are the area grows by 1 inch. The FLIR type imagers give a much clearer picture of what is going on.

Similar issue with voltage drop; you need to be able to record milivolts to get anything marginally useful.

 

[OzSolar]

FWIW, remember that the temp guns laser is just to show where you are pointing. The actual cone that it is averaging is about 60º so for every 2 inches away you are the area grows by 1 inch.

Good point

Similar issue with voltage drop; you need to be able to record milivolts to get anything marginally useful.

Not in my experience, even the cheaper meters can accurately measure mV in the ranges I'm talking about. When you load a system up with everything you can throw at it problem spots will show up pretty quickly with a DVM.

 

[Mr-Sandman]

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.

Everything is working as expected. While I don't have solid conclusion to root cause, I'm leaning towards an internal breaker failure due to bad contact connection that overheated and then started arcing during PV output. I'm pretty sure it was not a loose wire connection as the wire is still in tight in the lug. I was able to loosen the connection and remove the wire "not welded from heat".

At this point I'm not sure to be worried about these breakers or consider myself unlucky in getting a bad one that melted down. But I will be keeping a closer eye on them and I would suggest anyone else using the cheap Chinese DC breakers to do the same.

 

[Mattb4]

I have been using the Chtaixi DC 125a breaker for between my batteries, fuse and AIO. I have had no issues with heating but various Threads like this one got me thinking. I decided to upgrade to an MCCB (molded case circuit breaker) 160a that cost more than twice as much. Got it in the mail just yesterday. I am impressed how much more substantial the MCCB unit is. Pretty massive. See image of the difference in size.

I like the Allen head bolts to fasten the cable using ring terminals versus the smaller breaker requiring you to insert stripped wire and tighten down with screwdriver. Luckily I have a set of metric Allen head sockets for proper fastening. ETA: photo of breaker wired up, old breaker removed and with flash screen on AIO (load) side. Not sure if that is the correct location but I went with it.

 

[OzSolar]

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.

That still sounds high to me.

Ambient temp plus 20f seems normal in my experience. Anything over ambient plus 40f is a sign of a problem in my book. It would be great if others would chime in with actual numbers rather than speculation.

Would you mind humoring me and measuring the voltage drop across these connections when it's at full load?

What is the ambient temperature in the space?

Here's a thermal image from one of my systems at my house that I just happen to have to cover off of. It's been running almost 80 amps for a few hours on #4 welding cable. I only use Carling or Heinemann breakers. That's who make all (most?) of the Midnite breakers.


So

 

[Tomthumb62]

The Solar panels feed into the TOP of the breaker using 8 gauge wire and the SCC is hooked to the bottom of breaker.

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?

 

[Shimmy]

That still sounds high to me.

Ambient temp plus 20f seems normal in my experience. Anything over ambient plus 40f is a sign of a problem in my book. It would be great if others would chime in with actual numbers rather than speculation.

Depends a lot on the breaker design. GE was famous for needing to use the busbars of their panels as breaker heat sinks so that when you had a continuous load of over 300A on a continuous rated 400A breaker it would be unreliable. Interior temperature got too high for the busbars to sink any more heat.

20-40F above ambient is pretty normal though; maybe as high as 60F at the contacts (but falling quickly) using an imager. (All 80% of rated load.)

Would you mind humoring me and measuring the voltage drop across these connections when it's at full load?

This is really the magic question. I would recommend measuring it periodically and logging the current vs voltage drop.