Small (QO or Airpax-type) breakers in a distribution bank should be front ended with a suitable DC master breaker or fuse that has the capability to interrupt the available fault current. Ideally, the series combination should be rated but at a minimum, a coordination study should be undertaken.
I like to have primary protection on each string, as close to the battery as possible - preferably bolted to the battery terminal. Cable limiters are nice, but a TPL style fuse is easier to get. On May 16, 2010, at 16:13 , Kurt Albershardt wrote: > Voltage is not the issue here, it is current, and battery fault currents can > be staggering - far more than one would ever encounter in a typical AC system > fed from a distribution transformer. I have seen a 200A Class T fail to act > on an 48V inverter fault which resulted in welding the metal tabs of the fuse > holder (which had been greased with copper-laden Penetrox E) to their > sockets. That indicates a fault current well north of 200,000 amps, quite > possibly several times that. A fire ensued, which triggered the gas > protection system and fortunately resulted in almost no peripheral damage. > It did cost about $10k to recharge and recertify the Inergen system. The > inverter manufacturer was quite cagey on warranty replacement until they saw > the photos - at which point a replacement miraculously arrived by overnight > air. > > > > On May 15, 2010, at 9:43 , Drake Chamberlin wrote: > >> I did see a QO breaker fail to trip on a 24 volt DC system with only battery >> voltage behind it. It burned a #12 wire completely in two. >> >> >>> The 48v is a max rating not a nominal rating. >>> So yes only good for 12 and 24v systems. >>> >>> However with CBI breakers I don't understand why the need for QO for DC >>> anymore? >>> >>> jay >>> >>> peltz power >>> On May 15, 2010, at 6:28 AM, Rebekah Hren wrote: >> Drake Chamberlin >> Athens Electric >> OH License 44810 >> CO License 3773 >> NABCEP TM Certified PV Installer >> Office - 740-448-7328 >> Mobile - 740-856-9648
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