AC vs DC Panels and Breakers

Re: AC vs DC Panels and Breakers

Square D QO circuit breakers are readily available and they are relatively inexpensive. The QO breakers are indeed rated for 48 VDC, and their AIR is 5,000 A. I would urge caution in their use.

See: http://ecatalog.squared.com/pubs/Circuit%20Protection/Miniature%20Circuit%20Breakers/QO-QOB%20Circuit%20Breakers/0730CT9801R108.pdf

and: http://ecatalog.squared.com/pubs/Circuit%20Protection/Molded%20Case%20Circuit%20Breakers/Thermal%20Magnetic%20Molded%20Case%20Circuit%20Breakers/0601DB0401.pdf

They are probably best suited for combining “12 V” modules (i.e., STC Voc = ~22 V) in parallel to create a “12 V” array, or even for combining “18 V” modules (i.e., Evergreen) in parallel. However, the STC Voc of a “24 V” module is in the 44 V range (i.e., SolarWorld SW165).The Voc will approach/exceed 48 V once the ambient temperature drops below ~50 F, so the QO breaker is technically not suitable for “24 V” modules in cool-to-cold climates.

The QO circuit breaker’s AIR (Amps Interrupting Rating) of 5,000 A DC is fairly low for use as a battery breaker/disconnect. A shorted battery could easily supply 5,000 A or more, which means that the circuit breaker could be destroyed, or, even worse, short closed. In comparison, the big DC breakers used by MidNite, OutBack, and others are rated for 25,000 A to 50,000 AIR.

I did use QO breakers early on when my starter system was all 12 V array and 12 V battery bank. But, once I went to a 24 V / 12 V system, then a 36 V / 24 V system, and finally to a 48 V / 24 V system, all DC breakers were replaced with CBI's and Carlingswitch's from OutBack and MidNite.

HTH,
Jim / crewzer