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DC Circuit Breaker Fires

I don't know if any DC breakers are "Switch Duty".
SMA inverters often come with DC switches, but they still recommend interrupting current at the AC breaker first.

"

Which Square D or Schneider Electric circuit breakers have SWD (Switch-Duty) ratings?​

Product Line:
Circuit Breakers

Resolution:
Per UL 489, the switch duty rating label (SWD) may be applied to single pole, 15 and 20 A circuit breakers, 347 Vac or less that pass the special SWD test requirements. The SWD rating applies to breakers used for regularly switching fluorescent lights.
"

 
Hedges said:
I don't know if any DC breakers are "Switch Duty".
Click to expand...
Midnite Solar dc breakers are switch duty rated.
From their own website, "MidNite's breakers are rated to break the full rated load at the rated voltage repeatedly, with NO DAMAGE. Always use a properly sized breaker for disconnecting."

MidNite Solar Inc. Renewable Energy System Electrical Components and E-Panels

MidNite Solar is the industry leader and manufacture of quality Renewable Energy System electrical components and E-Panels.
www.midnitesolar.com
 
These polarized DC breakers are weird...

Suppose you put 3 PV strings in parallel, each string has wires rated for its current and a breaker.

Now suppose one string shorts, or mice eat the cable, whatever. Now we have 2 PV strings dumping current into the shorted string, in reverse.

The breaker is supposed to protect the wires of the shorted string against taking 2x their rated current from the other strings, that's why code around here mandates overcurrent protection when wiring strings in parallel.

But if the breaker catches fire when tripped with reverse current... hmmm.... wut?
 
peufeu said:
These polarized DC breakers are weird...

Suppose you put 3 PV strings in parallel, each string has wires rated for its current and a breaker.

Now suppose one string shorts, or mice eat the cable, whatever. Now we have 2 PV strings dumping current into the shorted string, in reverse.

The breaker is supposed to protect the wires of the shorted string against taking 2x their rated current from the other strings, that's why code around here mandates overcurrent protection when wiring strings in parallel.

But if the breaker catches fire when tripped with reverse current... hmmm.... wut?
Click to expand...

Exactly.
That is why I have said polarized breakers can't provide protection for PV strings, although they were sold in combiner boxes for that purpose.
I understand code now requires non-polarized in that application.

I think if you use a ganged breaker, so the overloaded breaker trips and turns off the other breakers which supply the current, that will work.
 
Damn, I just realized my breakers are polarized. I'm not paralleling strings, so it should be alright. There's no mention of non polarized breakers in the French code, they just say "breakers or DC disconnect".

Well, I'm glad I got this info, I'll probably add a linkage to gang them all together.
 
You have multiple breakers, but not parallel strings? Does each string have its own MPPT input? If so, ganging them shouldn't make a difference (neglecting any faults in SCC that might parallel them.)

Have you confirmed your polarize breakers are connected to PV string with the correct polarity?
 
Hedges said:
You have multiple breakers, but not parallel strings?
Click to expand...
Couldn't find DC disconnect switches, all out of stock except dubious quality on aliexpress and amazon, but DC breakers from a good manufacturer were available. I checked in the regulations, it said it was okay to use breakers instead, so I did. Due to the energy crisis in Europe, everyone's buying solar... Inverters are still available (unless you like Fronius) but it's the little things that have months of delays, like roof fastening accessories, disconnects, special snowflake mandated GFCIs, MC4's that aren't garbage, etc. Took a lot of time to get all the parts.

Hedges said:
Does each string have its own MPPT input? If so, ganging them shouldn't make a difference (neglecting any faults in SCC that might parallel them.)
Click to expand...
Yes, it should be fine.
Hedges said:
Have you confirmed your polarize breakers are connected to PV string with the correct polarity?
Click to expand...
Yes.
 
rodrick said:
Breakers are for over current protection, mag starters/contactors/switches are for turning power sources off
or on
she most likely assumed with over 200 posts that you must have learned something and maybe you were kidding her
she obviously didn’t know that you are a different kind of special with a very foul mouth and I’m sure she is sorry she had no intention to pick on a special needs person
Click to expand...
Never ever open a fuse supplied by a dc conductor that is energized. If the PV system is producing power and you open the fuse holder you will cause an arc that could burn and melt the fuse holder and start a fire. You should always use (for safety) a dc disconnect between the PV array and any other equipment.
 
Hedges said:
I don't know if any DC breakers are "Switch Duty".
SMA inverters often come with DC switches, but they still recommend interrupting current at the AC breaker first.

"

Which Square D or Schneider Electric circuit breakers have SWD (Switch-Duty) ratings?​

Product Line:
Circuit Breakers

Resolution:
Per UL 489, the switch duty rating label (SWD) may be applied to single pole, 15 and 20 A circuit breakers, 347 Vac or less that pass the special SWD test requirements. The SWD rating applies to breakers used for regularly switching fluorescent lights.
"

Click to expand...
I use a 2 of the Walfront8yz35e1mf-01 in my combiner box (16amp 250vdc) They are rated for mechanical 20,000 times and electrical life 10,000 times.
 
funny i have not said anything near that rude/crude and gotten kicked of for months on end... guess the female? members of this forum are a little more hardcore then some of the other northern members... sorry do not want to misgender any of you ;)
 
Jennifer said:
Further to my earlier post https://diysolarforum.com/threads/amazing-length-of-time-walking-after-a-2300v-arc-flash.28037/ be careful about selecting and wiring DC circuit breakers kids...


Also discussed here but a good reminder: https://diysolarforum.com/threads/dc-circuit-breaker-fires.30544/
Click to expand...

Since short circuit current is so close to max power current with solar panels, aren't these breakers essentially worthless for overcurrent protection? Therefore using a polarized circuit breaker is just increasing risk (fire). Is it better off just to use a DPDT switch to meet NEC code?
 
Last edited:
Correct, don't use breakers to protect PV home run wires from overcurrent. Size the wires to handle max current (ampacity 1.56x short circuit current.)

Breakers are either for PV disconnect, or to protect a single PV string that has shorted from being backfed by several other PV strings. In that case polarity or non-polar matters.

Most inverters these days take in one or two PV strings per MPPT and have built-in switch (DPST, not DPDT), or 4PST or 6PST depending on how many MPPT inputs.
 
There is a reason you don't see houses wires with fuses anymore. There is no reason a decent DC breaker will not protect your wiring, that is silly. I would use the double pole style just for complete isolation. Anecdotal demonstrations are just that. A breaker is fine for an occasional disconnect, good grief. When you get into very high current scenario's, and when you have extrememly static loads you tend to get fuses, because the cost of a 500A breaker would get silly. Further a fuse is better if you want/need a rapid disconnect and no trip curve. A fuse is generally more reliable, and doesn't suffer from degradation running close to it's trip current. For most use cases with modest current demands 'meh'.

I have a 240v 1A din driving some power supplies and relays with#20 feed wire. I've 'er tested it several times.
 
I use the langir's on my PV. The 15A's will trip on an overload when you don't swap it for the 25A as intended after doubling up strings. Even though the breaker protects the wire, I don't like to run heavier than my expectation. I ran #4 to my charging pedestal, it's on a 50A, because I don't want it pulling more than that causing other issues. YMMV
 
DPC said:
Looks like a knock off of a wearing house breaker
The ratings are a bit Suspect

It’s an iec breaker
Nothing wrong with that
Click to expand...
When evaluating DC breakers, the first thing I want to see is a test lab marking or report.
If not UL, at least TUV or other European test labs. Actual test reports are a bonus.
CE/UKCA markings can be self-certified, there is no enforcement other than requesting to see their file of documentation.

CCC is the compulsory communist Chinese marking for safety. You can be the judge of that.

If it says IEC/EN 60947-2, it has been certified by someone to meet that international standard (which is good).

Here is a great page:

What are the main international standards for low-voltage electrical equipment? | Quisure Circuit Breaker

What are the main international standards for low-voltage electrical equipment? What do the abbreviations and names represent?
www.quisure-circuit-breaker.com
 
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