Double Pole Vs Single pole Breakers

[JeepHammer]

I would start here...

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In the thread about arc over of DC circuits I *Tried* to point out metallic ionizatin, the 'Glow Discharge' or 'Ionizatin Kernel' and that differential is the cause,
But the resident 'Experts' that shouted me down and plastered the 'YouTube' videos not understanding what they were seeing it while watching it...
Saying that using fuses would burn the house/vehicle down.

It happened again in the high amperage relay/contactor thread,
The point of blowout, and differential weren't discussed at all, and when you bring it up you get shouted down.
If you can't figure out why a resistor is used between main power poles when 400A crosses the breaker contacts the size of a dime, then you don't understand the differential, or molten copper getting blown around the room...
If you have never seen a blowout or aftermath of a blowout, it's hard to grasp metal being turned into a superheated gas and molten copper splashing around everywhere... So it's easy to dismiss.
There is a reason the actual experts use resistors & diodes, so you DON'T have to see that first hand!

Differential is why you break BOTH legs of a DC circuit, everything from the 'Positive' breaker, through the load and back to the 'Negative' breaker becomes buffer for the Differential...

A high quality DC breaker will use a high powered magnet to disrupt the ELECTROMAGNETIC LINK attraction and will keep a 'Glow Discharge' bubble, or 'Ionizatin Kernel' from forming to promote the actual discharge arc.
When you figure out the electromagnetic link/ionizatin link, the breaker makes perfect sense.

The second type of breakers you will probably never see, it uses super dry, inert gas blowing the ionizatin bubble from between contacts, and arc over doesn't occur.

So, to that end,
You *Might* want to check out an arc supression breakers,
Maybe be a little more specific what type of breakers you are talking about since there are about a dozen or so commonly used DC breakers,
And knowing the difference between combined current (both volts & amps) instead of just amperage alone will help.

These are just suggestions, I'm NOT arguing with anyone OR recommending a product.
I would suggest you stay AWAY FROM...

Ferious metal contacts, iron/steel/tin. These ionize REALLY well and PROMOTE arc over.
This includes all the 'China' made ultra cheap breakers that rely on amps only (bimetal spring that has to heat and is slow to trip), and don't have a rare earth magnet to draw ionizatin out of the forming gap.

Ferious metal contacts pit, blow out and carbon up creating poor contact surface, which also cause arc over.
A breaker case full of carbon and metal dust make for poor safety devices.

Copper, or better yet silver contacts prevent welding/blowout and don't ionize nearly as much as ferious metals.
Something so hard the plasm has to ionize it into gas also work well, you will get pitting, but you won't have a breaker case full of metal dust.

*I* (Personally) won't use a cheap breaker.
I will look for the best deal on properly made breakers.
While the ones from 'China' *Might* be 'Approved' (or not no matter what the ink stamp on the case says, China counterfeits dogfood & toothpaste)
I choose to buy a breaker that is reliable through SEVERAL trip cycles, not one or two, *IF* that many.

It's up to everyone to decide what they need, but I'm hoping some research and education keeps people ACTUALLY SAFE!

 

[Supervstech]

AC, follows NEC code...

DC has so many potential issues and as such, it is best to listen to the experts, and get the right stuff!

 

[JeepHammer]

AC, follows NEC code...

DC has so many potential issues and as such, it is best to listen to the experts, and get the right stuff!

I agree, if you don't know EXACTLY what you are doing, go with a professional and high quality.
This is your safety we are talking about.

 

[offgriddle]

Something about, "differential", seems to contain a plausible argument for possibly considering fusing the negative side of a floating, (non earth grounded), DC system. If anybody has a link to a supplier of quality DC breakers that'd b cool.

 

[SolarRat]

I see, it's a phase thing. Makes sense why there's only one neutral for a 240 VAC appliance.
The neutral serves as the return path for each phase but the phases peak in different time domains, like a time share for multiple phases!

It's also the reason you want to turn off the multi-wire branch circuits when backfeeding both sides of your breaker panel with a 120v genny, so you don't overload the single neutral.

 

[SolarRat]

It is very commonly used in 220V AC systems. Typically L1 and L2 are through circuit breakers and Neutral is permanent. I won't go in details about that because it isn't relative to the question.

I think you mean 240v split phase systems. L1 and L2 are on the same circuit.

 

[svetz]

...ALL circuits are allowed smaller ground conductors than the load conductors....

I don't get that... the ground conductor needs to carry enough current to trip the breaker in the event of a fault. I can understand the wire could be smaller for that (only needs to carry the current for short period), but shouldn't there be a formula to specify the minimum gauge?

 

[SolarRat]

The importance of using a good DC circuit breaker (and why tripping both sides of a big circuit may be a good idea):

 

[John Frum]

The importance of using a good DC circuit breaker (and why tripping both sides of a big circuit may be a good idea):

Its not obvious to me why tripping both sides of a big circuit is indicated by this video.
Please explain.

 

[svetz]

That's more why you can't/shouldn't attempt to use an AC breaker (or switch) for DC. AC breakers make use of the fact that so many times per second (depending on frequency) the voltage is 0.

 

[JeepHammer]

Its not obvious to me why tripping both sides of a big circuit is indicated by this video.
Please explain.

Joey,
Intentionally or unintentionally, that's a video of a guy deliberately creating the perfect conditions for an arc.
The circuit is repeatedly opened and closed, VERY SLOWLY, to create the ionizatin bubble at the contact points.
Once that ionized kernel is formed, the actual arc can happen.
It takes the bubble first.

Think metal plating, ionized particles are moving from one side of the contact to the opposite polarity.
Once those ions are suspended in the air, and aren't either blown away by dry gas, or pulled away by the electromagnetic link with a magnet, they suspend momentarily around the metals they came off of.

Once enough of the metal particles are suspended, the actual plasma arc can happen.
Plasma arc is several thousand to million times stronger than the kernel forces...
Think arc welder that makes steel molten or vaporizes it in milliseconds.

This person repeatedly makes/breaks contact of an ACTIVE circuit, a full load resistance circuit,
To form the kernel, and allow just enough gap for an active arc to happen,
Once that active arc happens, they stretch it to the limits of the power source.

If you watch carefully, the switch is opened/closed several times SLOWLY to heat the metal, which also causes it to throw ions into the kernel,
And as the demonstration goes on, the resistance increases as the heating element heats up.
Electrical Resistance heating isn't a linier curve, it's exponential.

The more something heats, the higher the resistance goes up, this increases differential exponentially.
By the time they get around to DC, the ionizatin kernel is fully formed, the resistance in the Load is maximum, and the differential is highest.

Compared to a fuse or breaker, that opens ONCE in over Amp/Volt situations, it's not even close to a valid 'Test' or experiment for fuses or breakers.
There is a reason for voltage rating on breakers, just like the amperage load, that's the distance of the air gap, and the differential capable of jumping that air gap with an actual arc (not just some random ionizatin).

An example is the the Midnite solar video.
150V (at any given amperage open point) is a single breaker/single air gap.

300V is two breakers in series, with two air gaps, and half of each breaker as a ionizatin buffer, the connection between breakers.
While ions will give that buss between breakers a charge that can be measured, it's a voltage/current 'Step Down' so the second breaker air gap can control the current. It's also 4 times the air gap, and 4 chances to break the 600V in the circuit.

600V breakers use 4 of the singles in series, 3 'Step Downs' and and the 4th is guaranteed containment.

NOTHING withstands a plasma arc, it will consume all known conductors,
The hardest metals man can manufacture literally go up in smoke in a plasma arc (EDM Electronic Discharge Machining)
I machined the hardest metals with nothing more than an electrical current, simply burned them away (under controlled conditions) on a daily basis for 20+ years... And that's usually well under 20 amps.

It's differential in volts/amps that has to be controlled/contained to break a circuit.
Keeping the ionizatin contained is the easiest way to keep an arc from forming,
Keeping that arc from forming is several thousand times easier than trying to extinguish it once formed.
An ounce of prevention comes to mind...

Fusing/breakers are a science unto themselves, and since you can't see a magnetic or ionizatin field with the naked eye, it never occurs to most people what's actually going on when they watch people make an arc with relatively low amps/volts...

 

[Craig]

So in the end is there a problem and is it necessary with using dual pole DC breakers between PV and SCC, SCC and battery, Battery and Inverter?

Some have mentioned if grounded properly the breaker could be bad if I understand correctly.

My panels are grounded from their frame to earth with green grounding wire so I do not think that is the same as on a vehicle where the grounds or negative wire are all common



I never expected this topic to go so wild but I think I didn't properly post my question

 

[John Frum]

Joey,

I don't think you answered my question.
But honestly with my limited attention span for prose I can't be sure.
Thanks though.

 

[Supervstech]

I don't get that... the ground conductor needs to carry enough current to trip the breaker in the event of a fault. I can understand the wire could be smaller for that (only needs to carry the current for short period), but shouldn't there be a formula to specify the minimum gauge?

Nope...
Ground doesn’t carry ANY current.

neutral does.

in a microsecond, #22 copper can carry 10,000 amps.., so, for a shorted condition, the grounding conductor in a residential circuit only needs to be one size smaller than the current conductors.

 

[Supervstech]

I don't get that... the ground conductor needs to carry enough current to trip the breaker in the event of a fault. I can understand the wire could be smaller for that (only needs to carry the current for short period), but shouldn't there be a formula to specify the minimum gauge?

Also... for COMMERCIAL service, the grounding conductor has a calculation formula. Because arc fault conditions are much higher per potential service.
Residential service drops are fused at the transformer connection, and excessive fault current will blow the fuse.

 

[SolarRat]

Its not obvious to me why tripping both sides of a big circuit is indicated by this video.
Please explain.

Simply put, if he disconnected the negative cable at the same time as unlatching the knife switch, the arc would (should) stop almost instantly.

Good single pole DC breakers shouldn't arc in the first place, but an AC breaker might if used for DC.

 

[JeepHammer]

So in the end is there a problem and is it necessary with using dual pole DC breakers between PV and SCC, SCC and battery, Battery and Inverter?

No.
Dual pole simply use the entire load as a buffer, a 'Step Down' or resistor circuit between circuit poles.
It's perfectly acceptable and safe to use a positive only breaker as long as it's rated for the voltage you are working in.

I'll point out, we work in WATTS,
If you do the math on a fuse/breaker (or relay/contactor) you can figure out what Watts it will handle, even at higher voltages/lower amperage, or higher amps but lower volts.
The breaker points really don't care what the volts/amps are, just what energy is moving through before it heats/arc over, ect.

Some have mentioned if grounded properly the breaker could be bad if I understand correctly.

Only if you are using Ground Fault breaker, and neutral & ground are 'Bonded' (connected) someplace.
Ground Fault breakers MEASURE the differential between neutral and ground, if the two are bonded/connected, the differential measurement is screwed up.

My panels are grounded from their frame to earth with green grounding wire so I do not think that is the same as on a vehicle where the grounds or negative wire are all common.

Correct.
The earth ground to frame is in no way connected to the DC circuit inside the panel.
The two are insulated from each other.

The earth ground is there to direct/conduct lightening strike and air ionizatin from a near strike to 'Earth' so it doesn't over power and break through the insulation built into the DC circuits built into the panel.

I never expected this topic to go so wild but I think I didn't properly post my question

Another one of those things that seem 'Simple', but has an entire branch of electrical science to itself.

 

[svetz]

Nope...
Ground doesn’t carry ANY current.

In which case a ground serves no purpose. ? I think you missed that I was talking about fault conditions. Ground would carry a current for a brief time...until the breaker tripped.

 

[Supervstech]

In which case a ground serves no purpose. ? I think you missed that I was talking about fault conditions. Ground would carry a current for a brief time...until the breaker tripped.

No, I added in the fault loading info. Just remember, wire size is determined to flow current long term without heating above a specified temp. (60C in most cases for residential circuits) if time is shifted to fault conditions less than a second, most any conductor size will handle more than enough to trip or blow a fuse.

 

[svetz]

Yes! We're saying the same thing and arguing about it!
You have to expect that the ground will carry current (not the Ground doesn’t carry ANY current ), and it has to be sized appropriately (e.g., will survive long enough that a fuses/breaker (regardless of how slow) will give first).