DIN CIRCUIT BREAKER

[Clemj]

I am about to build my first small pv system consisting of 4 100 panels in 2s2p arrangement, a PowMr 60 amp MPPT solar charger, an SOK 12 v 206 Ah battery and an existing modified sine wave inverter to drive hydroponic lights . There will also be a 12volt output for an Icom IC7300 transceiver. I will have a circuit breaker in the pv line, and one between the charger and the battery ,and and for the 12 volt outlet. there will be a 150 amp fuse between the battery and the inverter, but no switch. The circuit breakers will be mounted in an ip65 clear cover power distribution box with din rail and a bus bar for the lower current negative connections. Is there any reason to use double pole circuit breakers rather than single pole, and can I fit 3 breakers in a 6 position box? Later expansion would be to go to 24 volts with 2 SOKs in series and a decent true sine wave inverter.

 

[HRTKD]

Double pole on the PV line is recommended. Somewhere around here someone explained why, but I don't remember. Single pole for everything else is OK, but a fuse immediately downstream of the battery is recommended over a breaker. There is a Midnite Solar breaker that works instead of a fuse. It's not cheap, but then again neither is a Class T fuse and holder.

 

[Hedges]

PV panels in a string can be quite high voltage, and no way to turn them off.

If breaker only interrupted PV+, and PV+ was shorted to frame somewhere, and you put a screwdriver on a non-grounded PV- or disconncted PV- wire, it could carry hazardous voltages.

I like to have PV string completely disconnected when working on wiring. If I don't have a 2-pole switch/breaker, I interrupt current then unplug both ends at MC connectors.

Since PV panels 2s2p don't require OCP, you can parallel them first then feed through a high enough current rating 2 pole breaker. Rating should be at least 1.56 x 2 x Isc. 2x is because you have 2 strings in parallel. 1.56x is to avoid nuisance tripping even if light conditions exceed 1 standard sun due to extra light reflected from clouds.

(As an aside, when it comes to DIN AC breakers, some are actually UL listed as circuit breakers, some as "supplemental protectors", meant for equipment but not branch circuit protection. Probably doesn't matter for inverter outputs, more for grid fed circuits. Most obvious difference seems to be longer plastic wings improving isolation between screw terminals of adjacent breakers. The listed breakers have been tested to interrupt more severe faults.)

 

[HRTKD]

When it comes to DIN AC breakers, some are actually UL listed as circuit breakers, some as "supplemental protectors", meant for equipment but not branch circuit protection. Probably doesn't matter for inverter outputs, more for grid fed circuits. Most obvious difference seems to be longer plastic wings improving isolation between screw terminals of adjacent breakers. The listed breakers have been tested to interrupt more severe faults.

Why did you bring up AC breakers? Did you mean DC breakers? I figure I better ask for the newbie, plus I'm confused.

I did make the initial mistake of buying AC dual pole breakers for the PV to MPPT circuit. The eggheads here were right to point that out and I changed that to DC dual pole breakers.

 

[Hedges]

Nope, no AC breakers in his question.
He has an inverter, so might have AC breakers there, or just switches because a small circuit.
I brought it up because UL 489 breakers vs. UL 1077 supplemental protectors distinction in new for me. Vendors will often call the supplemental protectors "breakers" but there is a distinction, not good for the same purposes.

But good to bring up the distinction between AC and DC rated breakers. (and a few have ratings for both.)

 

[RCinFLA]

Transformer-less GT inverters and HF all-In-One hybrid inverters usually do not isolate the PV inputs from AC output so the PV pos and neg lines are riding on top of AC output.

If you only put a single pole breaker on PV pos line you still can have high voltage AC riding on panels with single pole breaker turned off if inverter is still producing AC output.

It is absolutely important to get the physical orientation and polarity connection right on HV PV breakers for their arc extinguishing to work properly. It can be confusing and not well explained in breaker documentation. The '+' or '++' means the more positive voltage connection. For PV source positive line, it is the more positive voltage source.

To drive the created turn-off arc into the arc suppressing fins within the breaker, they usually have a magnet and use the arc plasma heat rise to direct the arc into the suppressor. Mounting breaker upside down causes the arc hot plasma to flare to the wrong direction and backwards wiring connection polarity will cause the magnet to drive the arc in the wrong direction.

Most of the low-cost mini-breakers with DIN mounts are non-UL certified. More importantly, their cases are made of non-fire resistant ABS plastics that will catch fire if improperly wired.

 

[Clemj]

Thanks for your responses. Breakers will be dc. I like the idea to completely isolate the panels in case of a different circuit path. The panels will be 2s 2p for the 12 volt, because of an unadvertised feature of the PowMr that only allows 80 volts open circuit when charging 12 volt systems. When I go to 24 volts, I will rewire for 4 s on the panels (VOC per panel ~ 22 volts and PowMr is good for 105 VOC at 24 volts) . Polarity will be observed on the circuit breakers. So a 2 pole breaker would take up 2 spaces on a din rail box, and each 1 pole would take 1 space.