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diy solar

Wiring polarity on DC breakers

The vendors of polarized breakers for PV (they aren't the manufacturers) will tell you to use them that way.
The manufacturers have achieved NRTL listing by demonstrating they interrupt current in one direction.

As has been demonstrated in the video of burning breaker, polarized breakers can only interrupt full voltage and current (or higher fault current) in one direction. So they can work if a power source is only on one side.

If used for bi-directional power, expect them to fail, but only when it really counts.

If used between a charge controller and battery, can they interrupt current from charge controller into battery? What about into a shorted/dead battery? Can they also interrupt fault current from battery into a shorted charge controller?

What about for multiple parallel PV strings? Can they turn off current flow into charge controller? Into a shorted wire? Now what if one PV string has a short, and now the breaker trips because it is carrying excessive amperage coming from all the other strings, dumping into the shorted one?

I say these polarized breakers can't provide the protection for which they are being used.

But if you only bought one, and are using it as a disconnect on input of charge controller, you're fine.
Thanks Hedges. I do plan to use it as the disconnect at the input of my charge controller. My PV string has panels in series and parallel, but I don’t see a scenario in which current will back feed from the charge controller to the PV panel string (thru the polarised breaker in the wrong direction).

By the way, given these things work by energising a coil - do they have a power consumption in normal use conditions, as a relay would?
 
Used as disconnect after combiner, so won't have good strings dumping into a bad string through this breaker.

Power consumption like any breaker would have, due to resistance. But no shunt current like a relay.

Typical household breakers are thermal-magnetic.

Some of the Midnight ones are Magnetic-hydraulic (some sort of shock absorber for slow trip). Because not thermal, not subject to variation with ambient temperature. That may be why Midnight says can be used at full current without derating.

These Schenider or similar breakers are probably also magnetic-hydraulic.
 
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