DC Circuit Breaker Fires

[DPC]

Years and years ago we used Westinghouse HKD breakers with a thermal magnetic 250 amp trip unit on the little battery locos.
That's breaker rated at up to 400 amps in that frame size, 600 volt AC and an interrupt capacity of 40,000 amps.
All this for a 90 volt loco a couple of small traction motors and battery bank of lead acid that weighed about a ton ( can't recall the ratings on batteries and motors ).

The three phase breaker was on the + DC side of the pack and used to protect the loco in case of a short and as a disconnect mean for the pack when it was removed for charging ( those were a 300 amp 90 volt exide unit as I recall )

The AC K frame breaker was wired so current went in one phase down a jumper connected that to the incoming of the middle phase and the that fed the top of the third phase... ( confused? all three sections of the three phase breaker were wired in series does that sound better ? )

All these little breakers are scary and made in China and some are fakes too.
Fuses only have to work once and they tend to be much more reliable.
Uses fuses for protection and breakers like these little biscuit units as Isolation devices and you will sleep better.

Or buy something expensive, big and proven to do the job

You know what really impressed the hell out of most guys I worked with who ran the trains?
When the power was out I would bring a Loco over and strip the wires off the coffee maker and feed it off the loco battery pack.
At least we had hot coffee while we waited for power to be restored.....

 

[rfbuehler]

Ok rather than starting a new thread I’ll ask here.

I want an breaker on an inverter. I have an expensive big breaker like shown in previous respons. The question I have is depending on weather it is charging or discharging the polarity changes same as the breakers on the batteries.

which way do you wire the?

 

[fromport]

The question I have is depending on weather it is charging or discharging the polarity changes same as the breakers on the batteries.

Polarity (+/-) doesn't change. the flow of the amps through the breakers changes.

which way do you wire the?

Get that information from the manufacturer. They should provide that. And they should know best.

 

[Bud Martin]

Ok rather than starting a new thread I’ll ask here.

I want an breaker on an inverter. I have an expensive big breaker like shown in previous respons. The question I have is depending on weather it is charging or discharging the polarity changes same as the breakers on the batteries.

which way do you wire the?

Are you talking about Inverter that has DC input and convert it to AC or you are talking about All In one unit that has charger and inverter?
If it is just inverter then you can use polarized DC breaker since current only flow on way into the inverter, not like the battery that has current flow both ways (charging and discharging) so it needs to be non-polarized DC breaker.
BTW, if you turn off the power to the inverter and let it sits for long period of time, the capacitor bank in the inverter will be discharged, so when you apply the power to the inverter, you will have high inrush current so you should have a way to pre-charge the capacitor bank first before turning on the breaker.

 

[DPC]

Does it need to be a breaker?

You might find a cheap fused disconnect used on ebay

Fuses are pretty darn hard to beat
The correct choice of fuses are superior to breakers for speed and current limiting in a short circuit

On my previous post I talked about a three phase breaker wired up for dc

Looked like this

The Ontario code had a provision for running ungrounded dc power supplies with a break on both the ac and dc side

You could do the same thing on the third phase break the negative

 

[Hedges]

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.
"

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

 

[littleharbor2]

I don't know if any DC breakers are "Switch Duty".

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

 

[peufeu]

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?

 

[Danke]

 

[Hedges]

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?

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.

 

[peufeu]

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.

 

[Hedges]

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?

 

[peufeu]

You have multiple breakers, but not parallel strings?

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.

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.)

Yes, it should be fine.

Have you confirmed your polarize breakers are connected to PV string with the correct polarity?

Yes.

 

[Pilot Bob]

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

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.

 

[Pilot Bob]

How else are you supposed to,disconnect an array?

Unless authorized by the manufacturer and certified by your approved testing agency.

 

[Hank Waconda]

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.
"

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

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.

 

[Daddy Tanuki]

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