QO Breaker - Interrupt [RE-wrenches]

[Peter Talmage]

Hi All,

Over the past years many of us have probably used QO
breakers for DC loads without high current limiting
fusing, so here is a little info to help us get a
little sleep at night. One thing that isn't usually
understood  is that battery systems themselves are
inherently  power  limiting. When very high currents
are drawn the battery and cabling resistance causes
very high voltage drops which limit the power.  It is
very tough to pull 5,000 amps in the typical RE 
battery bank system without a crash in the system
voltage. The breaker may see a high curent which will
trip it but t he lowered voltage will increase its
ability to interrupt safely. In my 25 years of
tripping OQ breakers with and with out in line high
interrupt current limiting devices I have never fried
a breaker nor popped the in line device.  In line high
current interrupt fuses are the code proper protection
 and should always be used. Fortunately in most cases
they will be redundant.

Yours,  Peter Talmage

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