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diy solar

Double Pole Vs Single pole Breakers

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).
I am not arguing, you are:p

really, I am just including extra info.
 
So, in the end, no reason to use double pole DC breakers anywhere in a PV system? (not arguing, just trying to get the thread back on track)
 
So, in the end, no reason to use double pole DC breakers anywhere in a PV system? (not arguing, just trying to get the thread back on track)
As I read it, DC should be double pole, and should be proper rated DC breakers.
 
Could you summarize why? I'm not seeing it (I see proper rated DC breakers, that's a given...it's why a double pole is useful).
 
As I read it, DC should be double pole, and should be proper rated DC breakers.
Maybe. On larger wattage/amp systems, probably a good move, just for safety's sake. On smaller systems, like maybe under 3-400 watts (16A @24VDC) I doubt there's anything worth worrying about.
 
What goes on the second pole? If the "safety" is for the plus/minus to the battery I don't get it. For example if one side fuses the breaker might be mechanically locked where the other side couldn't trip... in that case it would be better/safer to have two singles (to avoid the mechanical interlock preventing disconnecting the circuit).
 
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Then what's the safety issue and what's going on the second pole? Sorry...just not getting it.

That would never happen. They are designed and calibrated so if one side trips, both sides trip.
I agree, one side fusing (not tripping, but where fusing=DC arc weld) was a hypothetical breaker failure scenario where (because they were mechanically linked) the other side was stuck closed and therefore not providing any safety (that is two singles would be better than a double). I feel like I'm missing something.
 
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Then what's the safety issue and what's going on the second pole? Sorry...just not getting it.
Ok, do some experiments. Break one leg of a PV panel connection. Then use a voltmeter to check voltages between the various points, between the wires, across the breaker/switch, between the wires and ground (real ground, not frame ground), between the wires and the SCC frame.... anything you can measure. I'd be surprised if you didn't measure at least a few volts where you don't expect it.
 
High voltage pv breakers will have two poles.... one facing one polarity and one facing the other this insures that the breaker will open with highest electrical resilience to arc weld. The positive line is still the only line broken.

If a multi string combined circuit were to fault or a fault came from the other side it is going to work.

Its not going to burst into flames if you use a regular double pole dc breaker...... your monitor wont fizzle and zorch if you open positive and negative, you just bypass ground fault and short circuit safety is all ;)

A single pole breaker 150v and under is suitable for pv source circuits in negative grounded pv systems.
 
Then what's the safety issue and what's going on the second pole? Sorry...just not getting it.

Let's imagine a few cases:

Maybe there's a fault to ground on a panel
Maybe there's a wire from another panel string making contact with this one
Maybe one wire is shorted with an AC wire

Isolating both wires guaranties you can't electrocute yourself.

I agree, one side fusing (not tripping, but where fusing=DC arc weld) was a hypothetical breaker failure scenario where (because they were mechanically linked) the other side was stuck closed and therefore not providing any safety (that is two singles would be better than a double). I feel like I'm missing something.

A breaker is designed to trip even if the handle is blocked (e.g. you can't hold a breaker closed if it doesn't want to because of an over current fault for example) so this will never happen, if one side is stuck the other still breaks. Again double pole is safer than single (what if a single pole get stuck?).
 
I think it's finally penetrating that fossilized thing up there... thanks guys!

...A breaker is designed to trip even if the handle is blocked...
Wasn't sure if that was the case with DC breakers but it makes sense they'd be like AC breakers and it puts the final piece into place. Wasn't seeing why Rider would think there would be voltage anywhere if the breaker was on the positive side and ground was bonded to negative.
 
So, if it's good for the PV side because of the stray high voltage...should it be done on the battery too if you're >= 48V?
 
Ok
Let's imagine a few cases:

Maybe there's a fault to ground on a panel
Maybe there's a wire from another panel string making contact with this one
Maybe one wire is shorted with an AC wire

Isolating both wires guaranties you can't electrocute yourself.



A breaker is designed to trip even if the handle is blocked (e.g. you can't hold a breaker closed if it doesn't want to because of an over current fault for example) so this will never happen, if one side is stuck the other still breaks. Again double pole is safer than single (what if a single pole get stuck?).
Ok, all of the ground path between positive a.d negative is gone and the system cannot detect a fault properly.
So, if it's good for the PV side because of the stray high voltage...should it be done on the battery too if you're >= 48V?
No high voltage there!
 
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.

Is this because the potential has to be higher to sustain an arc over 2 gaps?
 
Ok so probably an impossible scenario. So say I have a 1 pole breaker on the positive PV line. That breaker is off or open. I then add the positive with the negative somewhere between single pole breaker and panel . what now happens to the negative line connected to my SCC could it have a current spike.

I'm really still as confused as ever. Some say you need them kernel says they make things worse.
 
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.
AH HAH .. I said thoughtfully whilst stroking my imaginary beard ..
IMG_20200211_140438.jpg
 
Im not sure i understand this "exercise".....

Reading from authorities on the matter is due. If you do not know, dont mess with this stuff. Sorry a little frustrating. By the time you are all done reading this, i wont have to defend any point and you will be within understanding of the principle of grounded pv, not grounding pv, 'grounded pv' i dont know everything and some is convention amd adhered to because it is the way ots done. If i do not understand totally why something is done i just make sure that all guidance is accepted and adhered to....
*by john wiles*

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