DC breaker shot a flame

[CaliSunHarvester]

I was working on my off-grid solar power installation today, adding class T fuses between the batteries and the bus bar (one class T for each battery).
The batteries are server rack style.

My steps:

1) shut down each battery's built-in breaker
2) put each battery to sleep (by pushing the reset button for 3 seconds)
3) changed the AIO from mode SBU to UTI
4) turned off the 250A breaker between the AIO and battery bus

Step 3 was probably not necessary as I had 7kW of pv input and the load was around 1kW only.

At this point, I thought it would be a good idea to also shut off the pv coming in.

5) turned off the 2 breakers between the 2 pv arrays and the AIO.

breaker 1 had 3100W (about 9.4A @ 330V)
breaker 2 had 4300W (about 16A @ 270V)

Both breakers are rated 25A. Breaker 2 had a flame shooting out on the right side.. I looked at it in an angle similar to the camera that took this photo.. about 2" were visible even though I looked at it in an angle, meaning the total length was probably 2.5" at least.

I installed 2 class T fuses and decided to put things back together. Everything is working "fine" now.

Do I need to replace the breaker that had the flame? The flame lasted perhaps 0.5 seconds.
I had bought it on Amazon and when I open the order, they don't offer the 25A version right now. The link points to a 15A version.

https://www.amazon.com/gp/product/B0BVVYX8VN/

pv input is at the top of these breakers and the load (AIO) is on the bottom.

Was there anything wrong with my shut down procedure? Should I have shut down the pv input as step (1)?

 

[Mattb4]

Typically you would avoid opening a breaker under load. Typically you shut off the SCC/AIO. Shut off PV and than shut off battery to AIO.

I would advise replacing the one the had fire coming from it.

 

[Q-Dog]

I would replace them even if they did not try to set your house on fire. Do you really trust a $10 "no name" safety device? I surely do not.

 

[Brucey]

I was working on my off-grid solar power installation today, adding class T fuses between the batteries and the bus bar (one class T for each battery).
The batteries are server rack style.

My steps:

1) shut down each battery's built-in breaker
2) put each battery to sleep (by pushing the reset button for 3 seconds)
3) changed the AIO from mode SBU to UTI
4) turned off the 250A breaker between the AIO and battery bus

Step 3 was probably not necessary as I had 7kW of pv input and the load was around 1kW only.

At this point, I thought it would be a good idea to also shut off the pv coming in.

5) turned off the 2 breakers between the 2 pv arrays and the AIO.

breaker 1 had 3100W (about 9.4A @ 330V)
breaker 2 had 4300W (about 16A @ 270V)

Both breakers are rated 25A. Breaker 2 had a flame shooting out on the right side.. I looked at it in an angle similar to the camera that took this photo.. about 2" were visible even though I looked at it in an angle, meaning the total length was probably 2.5" at least.

I installed 2 class T fuses and decided to put things back together. Everything is working "fine" now.

Do I need to replace the breaker that had the flame? The flame lasted perhaps 0.5 seconds.
I had bought it on Amazon and when I open the order, they don't offer the 25A version right now. The link points to a 15A version.

https://www.amazon.com/gp/product/B0BVVYX8VN/

pv input is at the top of these breakers and the load (AIO) is on the bottom.

Was there anything wrong with my shut down procedure? Should I have shut down the pv input as step (1)?

View attachment 239871

You need real DC breakers that can handle switching under load. Those cheap ones general catch on fire. Midnite Solar is generally the most popular and known for its fully rated performance over many activations. Alternatively IMO DC disconnects.

With over 300V on one of the arrays I'd suggest these they have assorted ratings- https://www.stellavolta.com/midnite-solar-mnepv30-600-2pp-circuit-breaker-30a-600vdc/

Remove the bridge connecting the two series 300V breakers and use one pole for positive and one for negative.

 

[CaliSunHarvester]

Typically you would avoid opening a breaker under load. Typically you shut off the SCC/AIO.

I did not really want to shut down the house, so turning off the AIO was not an option.
Next time, I will do it either early in the morning or after 7pm when there's 1Amp of current instead of 12:30pm with 16A.

I would replace them even if they did not try to set your house on fire. Do you really trust a $10 "no name" safety device?

The 25A version cost actually $14 but I get your point. I have seen some YouTube tear-down videos now where one of these breakers would practically never trip -- it lacked any mechanism.

The weird thing is, I have switched off the pv with these breakers maybe 2-5 times this year and never saw anything, not even a small arc.

I will look for a reputable brand this time. It's not a big investment compared to the other components.

 

[Brucey]

I would replace them even if they did not try to set your house on fire. Do you really trust a $10 "no name" safety device? I surely do not.

I don't see DC on those at all. Maybe AC?

 

[Bop]

I would replace them even if they did not try to set your house on fire. Do you really trust a $10 "no name" safety device? I surely do not.

Shame we don't have a shot of the other side- most MCBs have their details on the side not visible in his photo (including the company name and details)

 

[Q-Dog]

I don't see DC on those at all. Maybe AC?

Hmmm. I have some DC breakers here on my desk and both of them say DC right on the face. Some are Moeller (nice) and some are CNLongQ(cheap).

I did not really want to shut down the house, so turning off the AIO was not an option.
Next time, I will do it either early in the morning or after 7pm when there's 1Amp of current instead of 12:30pm with 16A.

I shut down the breakers during the night if I know I will need to work on something the next day. And I can get a lot done between 4 and 7am without losing production. But, I can also shut down the charge controllers before flipping the breaker if really need to or didn't plan ahead.

 

[Mattb4]

I don't see DC on those at all. Maybe AC?

Look close and you will see 500v with the DC flat line symbol versus AC wave symbol. Not that I would trust that.

 

[CaliSunHarvester]

Shame we don't have a shot of the other side

Easy to do. I pulled the 2 breakers a bit apart and while the left one looks "ok" from the far left side (original photo in post #1), there are black marks from the flame in the right breaker on the right side of the left breaker and on both sides of the right breaker.

Unfortunately, no text on the right side of the breaker.

I probably should replace both with a better product.

I don't see DC on those at all. Maybe AC

You are right, there's nothing saying DC on the product. Some of my other breakers do have the DC on it. The Amazon product title says "2 Pole DC Miniature Circuit Breaker, 500V 25 Amp DC". But that's rather thin, I agree.

 

[Mattb4]

I did not really want to shut down the house, so turning off the AIO was not an option.
Next time, I will do it either early in the morning or after 7pm when there's 1Amp of current instead of 12:30pm with 16A.



The 25A version cost actually $14 but I get your point. I have seen some YouTube tear-down videos now where one of these breakers would practically never trip -- it lacked any mechanism.

The weird thing is, I have switched off the pv with these breakers maybe 2-5 times this year and never saw anything, not even a small arc.

I will look for a reputable brand this time. It's not a big investment compared to the other components.

Yes doing it when there is no load would be wiser even with a better breaker. But if not turn off your house.

 

[CaliSunHarvester]

I shut down the breakers during the night if I know I will need to work on something the next day

Good habit. I will do that next time for work that takes longer, or as in this case, do the entire work at/after 8pm.

 

[Bananaman321]

I use IMO disconnects at my arrays for if I need to work on them in the daytime I can disconnect the power and at that time they will be under load.
A breaker serves no purpose it cannot be disconnected under load for its breaking potential will perform the same action at just a higher load.

If there's no load when you disconnect then simple MC4 connectors would suffice.

 

[CaliSunHarvester]

A breaker serves no purpose it cannot be disconnected under load for its breaking potential will perform the same action at just a higher load.

Yeah, that was my thinking. If 16A @ 270V DC cause a 2.5" flame, what would 50A cause? Because this breaker may not trip that fast.
My mounting wall is this nice dry 2x12 dimensional lumber.

 

[Mattb4]

I use IMO disconnects at my arrays for if I need to work on them in the daytime I can disconnect the power and at that time they will be under load.
A breaker serves no purpose it cannot be disconnected under load for its breaking potential will perform the same action at just a higher load.

If there's no load when you disconnect then simple MC4 connectors would suffice.

Opening and closing breakers under load accelerates wear. Tripping of a breaker for overload puts a great deal of stress on it and often results in replacement if done too many times. DC breakers are much more problematic due to arc interruption. One of the reasons folks are going to the T-Fuses is so that molten sand will break the arc.

MC 4 connectors work fine for opening a unloaded circuit but are more of a pain than flipping a breaker off.

 

[LakeHouse]

Was there anything wrong with my shut down procedure?

Yes and no... For an emergency shutdown, you should be able to just flip breakers. As others have said, please replace those no-name breakers, they clearly can't be trusted.
But for 'planned maintenance' as this was, you ideally would remove the load across the breaker before you turn it off. Your AIO should have a way to turn off solar power in a controlled way, for example by setting the mode to Utl (as you did) AND setting the max charge current to 0A. If it can't use the solar power directly, and can't send it to battery, it'll stop consuming solar power. It seems you can monitor the current from your arrays, so check that it's zero before disconnecting.

 

[CaliSunHarvester]

With over 300V on one of the arrays I'd suggest these they have assorted ratings- https://www.stellavolta.com/midnite-solar-mnepv30-600-2pp-circuit-breaker-30a-600vdc/

Remove the bridge connecting the two series 300V breakers and use one pole for positive and one for negative.

I appreciate the product suggestion. The second sentence about removing the bridge.. confuses me.

I looked at the stellavolta web site and it shows 2 installation options.

Option 1 only interrupts the positive line:


Option 2 resembles my current installation. It switches both conductors. However, I notice the array is at the bottom and the AIO is connected at the top. Aren't these DC breakers typically directional, and the standard is line (input) at top and load (output) at bottom?



I definitely don't feel comfortable with option 1 (switch only 1 conductor).

I've seen this brand MidNite mentioned frequently on this forum, always in positive context. I just want to make sure I install them correctly.

 

[Bop]

Hmmm. I have some DC breakers here on my desk and both of them say DC right on the face. Some are Moeller (nice) and some are CNLongQ(cheap).

I shut down the breakers during the night if I know I will need to work on something the next day. And I can get a lot done between 4 and 7am without losing production. But, I can also shut down the charge controllers before flipping the breaker if really need to or didn't plan ahead.

Klockner Moeller (sold as Eaton here in Australia) are a very good brand for DC MCB's, Schneider are very commonly used (especially in the new 1000v limit gridties), Hager are also a common and reliable brand, Earu are fairly common in the chinese stuff and have a reasonable reputation as well

(all of these are approved DC breakers for gridtie installs here, as you can't use non approved equipment here, they all have to pass Au/NZ electrical standards testing)

Never heard of the CNLongQ before ...

 

[meetyg]

Yes and no... For an emergency shutdown, you should be able to just flip breakers. As others have said, please replace those no-name breakers, they clearly can't be trusted.
But for 'planned maintenance' as this was, you ideally would remove the load across the breaker before you turn it off. Your AIO should have a way to turn off solar power in a controlled way, for example by setting the mode to Utl (as you did) AND setting the max charge current to 0A. If it can't use the solar power directly, and can't send it to battery, it'll stop consuming solar power. It seems you can monitor the current from your arrays, so check that it's zero before disconnecting.

The problem with alot of AIOs is that they continue to charge battery even when "turned off". That little switch on most AIOsdoesn't really turn it off, just the inverter part.
So turning off or putting the inverter in UTI mode won't necessarily help stopping it from pulling max power from the PV.

What we should do is first change "charger source" to utility only. That will stop the AIO from pulling PV power.
Then you can switch off and/or change to UTI, disconnect PV.

 

[Q-Dog]

Never heard of the CNLongQ before ...

Cheap Chinese. It says DC on the front. I wouldn't trust it to break under load, but I have a couple of them to isolate strings. I have an IMO disconnect to shut down the entire array.

OP should look at the IMO dosconnect. I don't think a breaker is needed there.

 

[Mattb4]

My habit, if I am working on the PV, is to flip off the PV breaker when I get up at 5AM in the morning. I then disconnect the common MC4 going to the array. Now I have time to do what I need. Add panels, change configuration improve connection or redo stuff.

 

[LakeHouse]

The problem with alot of AIOs is that they continue to charge battery even when "turned off". That little switch on most AIOsdoesn't really turn it off, just the inverter part.

Yeah. That's why I didn't tell him to turn it off. I said to switch the mode to Utl, set the max charge current to zero, and check that the current is zero before opening the breaker.

 

[Bananaman321]

Opening and closing breakers under load accelerates wear. Tripping of a breaker for overload puts a great deal of stress on it and often results in replacement if done too many times. DC breakers are much more problematic due to arc interruption. One of the reasons folks are going to the T-Fuses is so that molten sand will break the arc.

MC 4 connectors work fine for opening a unloaded circuit but are more of a pain than flipping a breaker off.

Schneider Electric's entry-level circuit breakers for basic applications have a high electrical life of 3,000–8,000 cycles and a high mechanical life of 15,000–30,000 cycles. However, Schneider Electric says that circuit breakers have a limited performance, and after 10,000 mechanical operations, 10,000 load current, and 50 maximum short circuit operations, the breaker can be replaced.

Though this is Quote for an AC rated breaker the action of the device is designed for disconnecting under load as are DC rated breakers. If you turn off a breaker in your house do you go around and make sure all your switches are off first? What about a water heater.


But if you're referring to the no name knockoff scamazon evil-Bay BS Breakers then your statement does hold water.

But if that be the case then it serves no purpose anyway except another fail point. Time to pony up.

 

[Brucey]

Schneider Electric's entry-level circuit breakers for basic applications have a high electrical life of 3,000–8,000 cycles and a high mechanical life of 15,000–30,000 cycles. However, Schneider Electric says that circuit breakers have a limited performance, and after 10,000 mechanical operations, 10,000 load current, and 50 maximum short circuit operations, the breaker can be replaced.

Though this is Quote for an AC rated breaker the action of the device is designed for disconnecting under load as are DC rated breakers. If you turn off a breaker in your house do you go around and make sure all your switches are off first? What about a water heater.


But if you're referring to the no name knockoff scamazon evil-Bay BS Breakers then your statement does hold water.

But if that be the case then it serves no purpose anyway except another fail point. Time to pony up.

There a potentially big DC arc to extinguish, versus AC.

 

[Mattb4]

Schneider Electric's entry-level circuit breakers for basic applications have a high electrical life of 3,000–8,000 cycles and a high mechanical life of 15,000–30,000 cycles. However, Schneider Electric says that circuit breakers have a limited performance, and after 10,000 mechanical operations, 10,000 load current, and 50 maximum short circuit operations, the breaker can be replaced.

Though this is Quote for an AC rated breaker the action of the device is designed for disconnecting under load as are DC rated breakers. If you turn off a breaker in your house do you go around and make sure all your switches are off first? What about a water heater.


But if you're referring to the no name knockoff scamazon evil-Bay BS Breakers then your statement does hold water.

But if that be the case then it serves no purpose anyway except another fail point. Time to pony up.

AC breakers are often used as switches. My training was to avoid doing this whenever practical. You do what you want funny man.