Sizing the combiner box circuit breaker?
Comments
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Series fuse rating will be on the data label on the back of your solar panels.
2.1 Kw Suntech 175 mono, Classic 200, Trace SW 4024 ( 15 years old but brand new out of sealed factory box Jan. 2015), Bogart Tri-metric, 460 Ah. 24 volt LiFePo4 battery bank. Plenty of Baja Sea of Cortez sunshine.
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If you cannot find the series fuse rating--Then a starting (not official) recommendation would be:
- 8.06 Amp Imp * 1.25 Isc derating * 1.25 NEC fuse/wiring derating = 12.6 Amps
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
My thanks, all!
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BB. said:If you cannot find the series fuse rating--Then a starting (not official) recommendation would be:
- 8.06 Amp Imp * 1.25 Isc derating * 1.25 NEC fuse/wiring derating = 12.6 Amps
--vtMaps
4 X 235watt Samsung, Midnite ePanel, Outback VFX3524 FM60 & mate, 4 Interstate L16, trimetric, Honda eu2000i -
Remember that most are rated at 40C, that has been an issue with high load circuits here in the past. On a hot day many times the breakers would trip. 40C isn't far from the normal afternoon high here, panel in hot sun I am sure can be much higher..
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Also, remember that breaker+fuses have AC and DC ratings--And DC ratings are usually much lower (operating voltage--Plus as said above, sometimes breaker/fuses are rated "differently" and not the same test conditions in different countries). As an example:
https://www.youtube.com/watch?v=HLX9cdB4TFQUploaded on Mar 17, 2011Why not to use an AC breaker on a DC PV circuit:
Testing a standard household Square D Homeline 15A circuit breaker on a 290vdc 12A PV array (28 Evergreen 120's in two parallel strings of 14, in about 90% full sun).Thorough destruction of the breaker, with fire shooting out of the sides for a while and molten copper spraying out several times. The arc was finally extinguished only by the terminal melting off the breaker... if it hadn't, it is unknown if the breaker would have eventually opened or not.
And remember that DC Arcs are much more difficult to extinguish than AC Arcs:
https://www.youtube.com/watch?v=Zez2r1RPpWY
Lots of details here... Answering one question "exactly" does not mean that the research+design is done (or done safely).
-Bill
Near San Francisco California: 3.5kWatt Grid Tied Solar power system+small backup genset -
solar_dave said:Remember that most are rated at 40C, that has been an issue with high load circuits here in the past. On a hot day many times the breakers would trip. 40C isn't far from the normal afternoon high here, panel in hot sun I am sure can be much higher..
A proper breaker for kaipo_boy's Combiner situation is the MidNite MNEPV 150 VDC-rated breaker. These appear to have an operating temperature range of -40 to + 65 C, and are very inexpensive, quality breakers. The Trip curves apply at 30 degrees C:
http://www.midnitesolar.com/pdfs/Q-Series(1).pdfBB, that dramatic video is very compelling on why NOT to use a breaker that has NO DC rating whatsoever (SQ D Homeline breaker). The SQ D QO, QOB, and QOU breakers DO have a limited Rating for DC (handle Ratings from 15 to 70 A, one, two, or three poles), and only to 48 VDC, at that.
Not to pick the nit too much. But, YES, use products that are RATED for the application, install components like breakers, in boxes/enclosures that are RATED for those breakers in that application, and so on ...
FWIW, Vic
Off Grid - Two systems -- 4 SW+ 5548 Inverters, Surrette 4KS25 1280 AH X2@48V, 11.1 KW STC PV, 4X MidNite Classic 150 w/ WBjrs, Beta KID on S-530s, MX-60s, MN Bkrs/Boxes. 25 KVA Polyphase Kubota diesel, Honda Eu6500isa, Eu3000is-es, Eu2000, Eu1000 gensets. Thanks Wind-Sun for this great Forum.
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